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Re: [Electronics_101] When is ground ground?

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  • Donald H Locker
    Ground is ground. Common usage is imprecise and dangerous. The power return wires are not ground, neither is the reference voltage network unless it is
    Message 1 of 27 , Mar 1, 2012
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      Ground is ground. Common usage is imprecise and dangerous.

      The power return wires are not ground, neither is the reference voltage network unless it is connected to the earth somehow.

      Donald.
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      ----- Original Message -----
      > From: "David" <dalbamonte@...>
      > To: "Electronics 101" <Electronics_101@yahoogroups.com>
      > Sent: Wednesday, February 29, 2012 10:13:32 PM
      > Subject: [Electronics_101] When is ground ground?
      > I have never been able to get my head around floating ground. I know
      > it is ground relative to a signal, but how does that affect safety?
      >
      > I have three pieces of equipment I want to hook together.
      >
      > One is a late 50'/early 60's Hammond Organ. I know the chassis is
      > floating ground because it is 2 wire mains.
      >
      > The second is a behringer mixer which has a three pin cord for the
      > wall and a weird connecter on the mixer itself. I assumed that signal
      > ground on this would be earth ground.
      >
      > The third is a keyboard which runs off a wall wart. I dont know
      > exactly why I am not concerned about the ground on this, but I am not.
      > I guess in reality I am not worried about it being compatible with the
      > mixer.
      >
      > The hammond has a rca in. I want to come out of the mixer effects out
      > and into the rca in. This will let me run my wall wart keyboard
      > through the leslie. I know the pin on the leslie is connected to a
      > capacitor which should isolate it from the dc operating voltage in the
      > tube amp on the Hammond. I also know that if the capacitor is bad it
      > will mess with the operating voltage on the Hammond and possibly not
      > be as loud. So i want to test the dc voltage on the pin on the rca.
      > But I am not comfortable about how the grounds would work so I checked
      > with a volt meter. I figured the Bheringer would ground the Hammond
      > through the ground on the signal cable if the difference was not too
      > great. I measured the voltage between the ground on the Behringer and
      > the Hammond. I was checking DC voltage and it was all over the place,
      > but seemed to be less than 150mV. Then I checked the ac voltage.
      > Between the behringer and the Hammond there was close to 18V AC. But
      > when I disconnected the hammond the ac was still high. I put the lead
      > on a screw on the switch plate (assumed ground) and got 26 V AC. Now I
      > am really puzzled.
      >
      > When is ground, ground? And how can I be sure I can hook these things
      > up without frying something?
      >
      >
      >
      > ------------------------------------
      >
      > Please trim excess when replyingYahoo! Groups Links
      >
      >
      >
    • Shawn Upton
      A floating chassis can pick up voltage, due to capacitive coupling effects.  Think of a hot wire (120Vac), brought near to the chassis.  Stray capacitive
      Message 2 of 27 , Mar 1, 2012
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        A "floating" chassis can pick up voltage, due to capacitive coupling effects.  Think of a hot wire (120Vac), brought near to the chassis.  Stray capacitive effects will couple from the wire to the chassis.  What is worse is when a "ground" wire picks up voltage, due to current on it.  Due to the resistance (and inductance) a wire can pick up a voltage across the wire itself.  Let's pretend for a moment that one piece of equipment outputs a signal, and that signal goes into say an amplifier.  The amplifier has a relatively low input impedance, so there is some current on the wires.  The low side of that wire won't be 0V across its length.  Had it been 0V at the output equipment, relative to its ground, it would be some other voltage at the other equipment, even if there was no difference between the chassis!

        Now, let's pretend that these two pieces of equipment were on different circuit breakers in your house.  Although that safety ground wire, going from the chassis to the electrical box, should have zero current on it--and thus, making that equipment chassis the same potential, it turns out that the ground wires (and especially the neutral wires) are not zero volts, relative to one another.  Too much coupling in equipment, due to stray capacitance.  The GND wires should be "close" but the neutral wire's won't be.


        Probably the best thing one can do is use isolation transformers on audio equipment, along with shielded cable.  The transformer allows DC (and low frequency, like 60Hz) differences, and hopefully reduces the possiblity of ground loops.

        In my head, "ground" refers to one of two things: the earth outside my house, and a voltage node that is reasonably close to zero volts.  Once a signal travels a TBD distance, "grounds" stop being the same potential--unless if they happen to be by design or by chance.

         
        Shawn Upton, KB1CKT
        NAQCC 4723


        ________________________________
        From: David <dalbamonte@...>
        To: Electronics_101@yahoogroups.com
        Sent: Wednesday, February 29, 2012 10:13 PM
        Subject: [Electronics_101] When is ground ground?


         
        I have never been able to get my head around floating ground. I know it is ground relative to a signal, but how does that affect safety?

        I have three pieces of equipment I want to hook together.

        One is a late 50'/early 60's Hammond Organ. I know the chassis is floating ground because it is 2 wire mains.

        The second is a behringer mixer which has a three pin cord for the wall and a weird connecter on the mixer itself. I assumed that signal ground on this would be earth ground.

        The third is a keyboard which runs off a wall wart. I dont know exactly why I am not concerned about the ground on this, but I am not. I guess in reality I am not worried about it being compatible with the mixer.

        The hammond has a rca in. I want to come out of the mixer effects out and into the rca in. This will let me run my wall wart keyboard through the leslie. I know the pin on the leslie is connected to a capacitor which should isolate it from the dc operating voltage in the tube amp on the Hammond. I also know that if the capacitor is bad it will mess with the operating voltage on the Hammond and possibly not be as loud. So i want to test the dc voltage on the pin on the rca. But I am not comfortable about how the grounds would work so I checked with a volt meter. I figured the Bheringer would ground the Hammond through the ground on the signal cable if the difference was not too great. I measured the voltage between the ground on the Behringer and the Hammond. I was checking DC voltage and it was all over the place, but seemed to be less than 150mV. Then I checked the ac voltage. Between the behringer and the Hammond there was close to 18V AC.
        But when I disconnected the hammond the ac was still high. I put the lead on a screw on the switch plate (assumed ground) and got 26 V AC. Now I am really puzzled.

        When is ground, ground? And how can I be sure I can hook these things up without frying something?




        [Non-text portions of this message have been removed]
      • Ron Wright, N9EE
        Ground is a central point hopefully common to all gear in a system. It could be say 4000 V difference between what is ground 3 blocks away. However, some
        Message 3 of 27 , Mar 1, 2012
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          Ground is a central point hopefully common to all gear in a system. It could be say 4000 V difference between what is ground 3 blocks away.

          However, some equipment that has say plastic enclosures where one cannot come in contact with any metal or electrical parts the ground for this piece of equipment would have its own ground inside and not connected to other equipment grounds. TVs are one example.

          Ground is a zero voltage point, but may be zero to that piece of gear and may be at a different voltage to another piece of equipment ground.

          We should not get into RF grounds here for they are much more complex, but for safety equipment where the operators can come in contact with metal and possible electrical voltages these metals are "gounded", that is connected with physical metal or wires together so they will be at the same voltage, zero for reference.

          We typically like to bring all these grounds to Earth ground, the actual dirt around the equipment.

          With your equipment that has either a 2 prong AC plug or wal-wart the chassis are covered and not exposed. However, when connecting them together there needs to be a reference for the signals to work together, but this does not have to be the safety ground of a chassis, but must have some sort of reference point.

          I think you are trying to get a safety or common ground on your equipment. Often this will only be thru the interconnecting cables, but if want a safety ground then the chassis's or power supply grounds would need to be connected.

          Ground is a zero voltage point, but might be at different voltages for different pieces of gear. I've seen PCs get grounded to other equipment and the PC would shut down. Why, its ground did not like being grounded to Earth ground or other equipment grounds. This was in the design.

          In most equipment ground is the zero voltage point all other voltages operate in reference to so the gear can function, but these grounds might not be at other equipment grounds; different voltage. Again has to be in the design.

          73, ron, n9ee/r


          --- In Electronics_101@yahoogroups.com, "David" <dalbamonte@...> wrote:
          >
          > I have never been able to get my head around floating ground. I know it is ground relative to a signal, but how does that affect safety?
          >
          > I have three pieces of equipment I want to hook together.
          >
          > One is a late 50'/early 60's Hammond Organ. I know the chassis is floating ground because it is 2 wire mains.
          >
          > The second is a behringer mixer which has a three pin cord for the wall and a weird connecter on the mixer itself. I assumed that signal ground on this would be earth ground.
          >
          > The third is a keyboard which runs off a wall wart. I dont know exactly why I am not concerned about the ground on this, but I am not. I guess in reality I am not worried about it being compatible with the mixer.
          >
          > The hammond has a rca in. I want to come out of the mixer effects out and into the rca in. This will let me run my wall wart keyboard through the leslie. I know the pin on the leslie is connected to a capacitor which should isolate it from the dc operating voltage in the tube amp on the Hammond. I also know that if the capacitor is bad it will mess with the operating voltage on the Hammond and possibly not be as loud. So i want to test the dc voltage on the pin on the rca. But I am not comfortable about how the grounds would work so I checked with a volt meter. I figured the Bheringer would ground the Hammond through the ground on the signal cable if the difference was not too great. I measured the voltage between the ground on the Behringer and the Hammond. I was checking DC voltage and it was all over the place, but seemed to be less than 150mV. Then I checked the ac voltage. Between the behringer and the Hammond there was close to 18V AC. But when I disconnected the hammond the ac was still high. I put the lead on a screw on the switch plate (assumed ground) and got 26 V AC. Now I am really puzzled.
          >
          > When is ground, ground? And how can I be sure I can hook these things up without frying something?
          >
        • Scrolling8
          Unfortunately on many pieces of older equipment unless you have a detailed schematic you will never know what the original designer intended for that specific
          Message 4 of 27 , Mar 1, 2012
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            Unfortunately on many pieces of older equipment unless you have a detailed schematic you will never know what the original designer intended for that specific equipment. Many times racked pieces of equipment had extensive circuitry connected and a point was chosen as a reference point for taking readings from. This ref. point many times was the chassis that the electronic boards were mounted in. Often this point was never intended to be grounded as what todays definition of grounded means. Many times the chassis actually carries current from parts of the circuit so it would not be a good idea to ground this. In fact making sure it is properly isolated would be more important. From an electrical point of view the most important part of the circuit to have a ground connection is the power supply portion of the device. And a point to remember is to test handle this equipment chassis only when the power is removed. And if you must test this equipment use you ref. points not ground unless that is what you intend. Also all amplifier connection must be secure and tight so as not to introduce any unwanted radio signals that can enter on any open wiring.

            Note: many times floating ground is really talking about this ref. point but not always. In many instances improperly connected power systems may be left floating (i.e. no connection of the neutral line at the power source to ground) and if you are taking a meter and trying to check a circuit to ground your readings will not mean a thing.





            -----Original Message-----
            From: David <dalbamonte@...>
            To: Electronics_101 <Electronics_101@yahoogroups.com>
            Sent: Wed, Feb 29, 2012 9:13 pm
            Subject: [Electronics_101] When is ground ground?





            I have never been able to get my head around floating ground. I know it is ground relative to a signal, but how does that affect safety?

            I have three pieces of equipment I want to hook together.

            One is a late 50'/early 60's Hammond Organ. I know the chassis is floating ground because it is 2 wire mains.

            The second is a behringer mixer which has a three pin cord for the wall and a weird connecter on the mixer itself. I assumed that signal ground on this would be earth ground.

            The third is a keyboard which runs off a wall wart. I dont know exactly why I am not concerned about the ground on this, but I am not. I guess in reality I am not worried about it being compatible with the mixer.

            The hammond has a rca in. I want to come out of the mixer effects out and into the rca in. This will let me run my wall wart keyboard through the leslie. I know the pin on the leslie is connected to a capacitor which should isolate it from the dc operating voltage in the tube amp on the Hammond. I also know that if the capacitor is bad it will mess with the operating voltage on the Hammond and possibly not be as loud. So i want to test the dc voltage on the pin on the rca. But I am not comfortable about how the grounds would work so I checked with a volt meter. I figured the Bheringer would ground the Hammond through the ground on the signal cable if the difference was not too great. I measured the voltage between the ground on the Behringer and the Hammond. I was checking DC voltage and it was all over the place, but seemed to be less than 150mV. Then I checked the ac voltage. Between the behringer and the Hammond there was close to 18V AC. But when I disconnect ed the hammond the ac was still high. I put the lead on a screw on the switch plate (assumed ground) and got 26 V AC. Now I am really puzzled.

            When is ground, ground? And how can I be sure I can hook these things up without frying something?









            [Non-text portions of this message have been removed]
          • David
            ... I m not sure the Hammond came with a polarized plug and I am sure it has been replaced at least once prior to when I got it. I will check with the Hammond
            Message 5 of 27 , Mar 1, 2012
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              Thanks richard:

              --- In Electronics_101@yahoogroups.com, "rtstofer" <rstofer@...> wrote:
              >
              > --- In Electronics_101@yahoogroups.com, "David" <dalbamonte@> wrote:
              > > One is a late 50'/early 60's Hammond Organ. I know the chassis is floating ground because it is 2 wire mains.
              > >
              >
              > There is a possibility that the chassis is grounded through the neutral. This was (and probably still is) a common scheme. The manufacturer knows that the neutral should be grounded (somewhere) and they know that the wide blade on the outlet should be the neutral. So, they connect it to the chassis. They also provide a polarized plug.
              >

              I'm not sure the Hammond came with a polarized plug and I am sure it has been replaced at least once prior to when I got it. I will check with the Hammond gurus to see which wire gets connected to nuetral.


              > Back in the bad old days people would sometimes change the plugs to a style that wasn't polarized. No problem as long as they didn't touch the metal. But just lose a knob and touch the metal shaft of a potentiometer while barefoot on the garage floor and see what happens. There's a reason I know this!
              >
              I know the metal column in my garage/studio/man cave is ground and my telecaster/Champ is not. Also learned the hard way.

              David
            • David
              That is what has me worried.
              Message 6 of 27 , Mar 1, 2012
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                That is what has me worried.

                --- In Electronics_101@yahoogroups.com, Donald H Locker <dhlocker@...> wrote:
                >
                > Ground is ground. Common usage is imprecise and dangerous.
                >
                > The power return wires are not ground, neither is the reference voltage network unless it is connected to the earth somehow.
                >
                > Donald.
                > --
              • Kirk McLoren
                thus the use of isolation transformers Nemo dat quod non habet ________________________________ From: David To:
                Message 7 of 27 , Mar 1, 2012
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                  thus the use of isolation transformers



                  Nemo dat quod non habet


                  ________________________________
                  From: David <dalbamonte@...>
                  To: Electronics_101@yahoogroups.com
                  Sent: Thursday, March 1, 2012 9:31 AM
                  Subject: [Electronics_101] Re: When is ground ground?



                   

                  That is what has me worried.

                  --- In Electronics_101@yahoogroups.com, Donald H Locker <dhlocker@...> wrote:
                  >
                  > Ground is ground. Common usage is imprecise and dangerous.
                  >
                  > The power return wires are not ground, neither is the reference voltage network unless it is connected to the earth somehow.
                  >
                  > Donald.
                  > --




                  [Non-text portions of this message have been removed]
                • David
                  ... [snip] Thanks for the explanation. just because I sniped it doesnt mean i did not comprehend. ... Are you talking isolation transformers on the input or
                  Message 8 of 27 , Mar 1, 2012
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                    --- In Electronics_101@yahoogroups.com, Shawn Upton <kb1ckt@...> wrote:
                    >
                    [snip] Thanks for the explanation. just because I sniped it doesnt mean i did not comprehend.

                    >>
                    > Probably the best thing one can do is use isolation transformers on audio equipment, along with shielded cable.  The transformer allows DC (and low frequency, like 60Hz) differences, and hopefully reduces the possiblity of ground loops.
                    >
                    Are you talking isolation transformers on the input or on the power. The Leslie has isolation transformers which go between it an the organ. That is why it is easy to adapt the leslie to use a guitar amp as input. The power isolation transformers are pricy. Anyone know of an inexpensive one? In genereal I am not getting a lot of hum. In the mean time I am using a star configuration for powering all my equipment.

                    > In my head, "ground" refers to one of two things: the earth outside my house, and a voltage node that is reasonably close to zero volts.  Once a signal travels a TBD distance, "grounds" stop being the same potential--unless if they happen to be by design or by chance.
                    >
                    Does that mean I should not worry about the voltage measured between the two devices? 26VAC seems excessive.
                  • David
                    ... [snip] ... The keyboard in my example is another. That is one of the reasons I am not worried about it. ... That is one of the things I am concened about.
                    Message 9 of 27 , Mar 1, 2012
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                      --- In Electronics_101@yahoogroups.com, "Ron Wright, N9EE" <mccrpt@...> wrote:
                      >
                      [snip]
                      >
                      > However, some equipment that has say plastic enclosures where one cannot come in contact with any metal or electrical parts the ground for this piece of equipment would have its own ground inside and not connected to other equipment grounds. TVs are one example.
                      >
                      The keyboard in my example is another. That is one of the reasons I am not worried about it.

                      > Ground is a zero voltage point, but may be zero to that piece of gear and may be at a different voltage to another piece of equipment ground.
                      >
                      That is one of the things I am concened about. In this case the connection of a peice of tube gear to IC gear. The tube stuff seems like it works by modulating an applied high DC voltage. The use capacitance coupling to keep one part of the circuite from interfering with the voltage requirements of the nexts stage.

                      > We should not get into RF grounds here for they are much more complex, but for safety equipment where the operators can come in contact with metal and possible electrical voltages these metals are "gounded", that is connected with physical metal or wires together so they will be at the same voltage, zero for reference.
                      >
                      > We typically like to bring all these grounds to Earth ground, the actual dirt around the equipment.
                      >
                      > With your equipment that has either a 2 prong AC plug or wal-wart the chassis are covered and not exposed. However, when connecting them together there needs to be a reference for the signals to work together, but this does not have to be the safety ground of a chassis, but must have some sort of reference point.
                      >

                      > I think you are trying to get a safety or common ground on your equipment. Often this will only be thru the interconnecting cables, but if want a safety ground then the chassis's or power supply grounds would need to be connected.
                      >
                      Yes. I would like a safety ground. When interconnecting multiple guitar amps the practice used to be to disconnect the ground on the plug on all but one amplifier. Then the common ground is made by the shield on the interconnected guitar cables. I was thinking the mixer would be ground and then the cable would provide ground. I was stopped in step one when I found the shield on the mixer to be 26V (18VAC to the hammond). The hammond was plugged in but not turned on during this test.

                      My plan was. Fire up the mixer, test to ground on the hammond. Then if I wasnt too unhappy with the results, fire up the hammond and check again. Then I was going to check tip to tip for dc voltage. I was stopped at step one.

                      > Ground is a zero voltage point, but might be at different voltages for different pieces of gear. I've seen PCs get grounded to other equipment and the PC would shut down. Why, its ground did not like being grounded to Earth ground or other equipment grounds. This was in the design.
                      >
                      > In most equipment ground is the zero voltage point all other voltages operate in reference to so the gear can function, but these grounds might not be at other equipment grounds; different voltage. Again has to be in the design.
                      >

                      The hammond has an RCA input which I was hoping would provide the common ground, but I do not know what the limitation are regarding the different ground point.

                      David
                    • Donald H Locker
                      Besides checking voltage between two pieces of equipment, also check the current. It is possible for two pieces of unconnected and floating (with respect to
                      Message 10 of 27 , Mar 1, 2012
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                        Besides checking voltage between two pieces of equipment, also check the current. It is possible for two pieces of unconnected and floating (with respect to earth) equipment to many volts different, but have essentially no leakage such that they can be safely connected together and to earth. If the current between the two is less than a few milliamps, you should be safe. If more, more research into why they so want to exchange charge is in order.

                        Donald.
                        --
                        *Plain Text* email -- it's an accessibility issue
                        () no proprietary attachments; no html mail
                        /\ ascii ribbon campaign - <www.asciiribbon.org>

                        ----- Original Message -----
                        > From: "David" <dalbamonte@...>
                        > To: "Electronics 101" <Electronics_101@yahoogroups.com>
                        > Sent: Thursday, March 1, 2012 1:23:23 PM
                        > Subject: [Electronics_101] Re: When is ground ground?
                        > --- In Electronics_101@yahoogroups.com, "Ron Wright, N9EE"
                        > <mccrpt@...> wrote:
                        > >
                        > [snip]
                        > >
                        > > However, some equipment that has say plastic enclosures where one
                        > > cannot come in contact with any metal or electrical parts the ground
                        > > for this piece of equipment would have its own ground inside and not
                        > > connected to other equipment grounds. TVs are one example.
                        > >
                        > The keyboard in my example is another. That is one of the reasons I am
                        > not worried about it.
                        >
                        > > Ground is a zero voltage point, but may be zero to that piece of
                        > > gear and may be at a different voltage to another piece of equipment
                        > > ground.
                        > >
                        > That is one of the things I am concened about. In this case the
                        > connection of a peice of tube gear to IC gear. The tube stuff seems
                        > like it works by modulating an applied high DC voltage. The use
                        > capacitance coupling to keep one part of the circuite from interfering
                        > with the voltage requirements of the nexts stage.
                        >
                        > > We should not get into RF grounds here for they are much more
                        > > complex, but for safety equipment where the operators can come in
                        > > contact with metal and possible electrical voltages these metals are
                        > > "gounded", that is connected with physical metal or wires together
                        > > so they will be at the same voltage, zero for reference.
                        > >
                        > > We typically like to bring all these grounds to Earth ground, the
                        > > actual dirt around the equipment.
                        > >
                        > > With your equipment that has either a 2 prong AC plug or wal-wart
                        > > the chassis are covered and not exposed. However, when connecting
                        > > them together there needs to be a reference for the signals to work
                        > > together, but this does not have to be the safety ground of a
                        > > chassis, but must have some sort of reference point.
                        > >
                        >
                        > > I think you are trying to get a safety or common ground on your
                        > > equipment. Often this will only be thru the interconnecting cables,
                        > > but if want a safety ground then the chassis's or power supply
                        > > grounds would need to be connected.
                        > >
                        > Yes. I would like a safety ground. When interconnecting multiple
                        > guitar amps the practice used to be to disconnect the ground on the
                        > plug on all but one amplifier. Then the common ground is made by the
                        > shield on the interconnected guitar cables. I was thinking the mixer
                        > would be ground and then the cable would provide ground. I was stopped
                        > in step one when I found the shield on the mixer to be 26V (18VAC to
                        > the hammond). The hammond was plugged in but not turned on during this
                        > test.
                        >
                        > My plan was. Fire up the mixer, test to ground on the hammond. Then if
                        > I wasnt too unhappy with the results, fire up the hammond and check
                        > again. Then I was going to check tip to tip for dc voltage. I was
                        > stopped at step one.
                        >
                        > > Ground is a zero voltage point, but might be at different voltages
                        > > for different pieces of gear. I've seen PCs get grounded to other
                        > > equipment and the PC would shut down. Why, its ground did not like
                        > > being grounded to Earth ground or other equipment grounds. This was
                        > > in the design.
                        > >
                        > > In most equipment ground is the zero voltage point all other
                        > > voltages operate in reference to so the gear can function, but these
                        > > grounds might not be at other equipment grounds; different voltage.
                        > > Again has to be in the design.
                        > >
                        >
                        > The hammond has an RCA input which I was hoping would provide the
                        > common ground, but I do not know what the limitation are regarding the
                        > different ground point.
                        >
                        > David
                        >
                        >
                        >
                        > ------------------------------------
                        >
                        > Please trim excess when replyingYahoo! Groups Links
                        >
                        >
                        >
                      • Howard Hansen
                        ... I can t add anything to what has been previously said about What is ground? . However, you can make some easy checks with a volt meter s ohm scale to see
                        Message 11 of 27 , Mar 1, 2012
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                          On 2/29/2012 9:13 PM, David wrote:
                          >
                          > I have never been able to get my head around floating ground. I know
                          > it is ground relative to a signal, but how does that affect safety?
                          >
                          > I have three pieces of equipment I want to hook together.
                          >
                          > One is a late 50'/early 60's Hammond Organ. I know the chassis is
                          > floating ground because it is 2 wire mains.
                          >
                          > The second is a behringer mixer which has a three pin cord for the
                          > wall and a weird connecter on the mixer itself. I assumed that signal
                          > ground on this would be earth ground.
                          >
                          > The third is a keyboard which runs off a wall wart. I dont know
                          > exactly why I am not concerned about the ground on this, but I am not.
                          > I guess in reality I am not worried about it being compatible with the
                          > mixer.
                          >
                          > The hammond has a rca in. I want to come out of the mixer effects out
                          > and into the rca in. This will let me run my wall wart keyboard
                          > through the leslie. I know the pin on the leslie is connected to a
                          > capacitor which should isolate it from the dc operating voltage in the
                          > tube amp on the Hammond. I also know that if the capacitor is bad it
                          > will mess with the operating voltage on the Hammond and possibly not
                          > be as loud. So i want to test the dc voltage on the pin on the rca.
                          > But I am not comfortable about how the grounds would work so I checked
                          > with a volt meter. I figured the Bheringer would ground the Hammond
                          > through the ground on the signal cable if the difference was not too
                          > great. I measured the voltage between the ground on the Behringer and
                          > the Hammond. I was checking DC voltage and it was all over the place,
                          > but seemed to be less than 150mV. Then I checked the ac voltage.
                          > Between the behringer and the Hammond there was close to 18V AC. But
                          > when I disconnected the hammond the ac was still high. I put the lead
                          > on a screw on the switch plate (assumed ground) and got 26 V AC. Now I
                          > am really puzzled.
                          >
                          > When is ground, ground? And how can I be sure I can hook these things
                          > up without frying something?
                          >
                          I can't add anything to what has been previously said about "What is
                          ground?". However, you can make some easy checks with a volt meter's
                          ohm scale to see if it is safe to connect the organ and keyboard to the
                          mixer. Measure the resistance between each pin on the Hammond Organ's
                          output connector and each pin on the AC power plug. It should be
                          infinite. Repeat the same test with input pins of the mixer and its AC
                          power plug. Repeat the same test with the output pins of the keyboard
                          and its
                          AC power plug.

                          If all the readings are infinite than is is safe to connect the organ
                          and keyboard to the mixer.
                          If only the mixer shows a low resistance between its AC power plug's
                          ground pin and one or more of its input pins than it is safe to connect
                          the organ and keyboard to the mixer.

                          Howard.


                          [Non-text portions of this message have been removed]
                        • Randy
                          From a lightning-protection standpoint, all ground rods need to be connected together with a heavy conductor, and all lines entering a structure would use an
                          Message 12 of 27 , Mar 1, 2012
                          • 0 Attachment
                            From a lightning-protection standpoint, all ground rods need to be
                            connected together with a heavy conductor, and
                            all lines entering a structure would use an "SPE", single-point-entry;
                            these grounds would tie together to a bulkhead of some sort at that
                            point, as would the building ground, and maybe one or more ground rods
                            for the bulkhead itself. Typically, the electrical ground and neutral
                            wires are tied together at the breaker box, regardless, AFAIK. Whatever
                            "ground" the telco, cable TV, etc., are used would also tie to this
                            bulkhead, and the lines would also enter the building at that same
                            point. If you have a ground rod connected to Device A, and a different
                            ground rod connected to Device B, without the two ground rods being tied
                            together with a heavy conductor, there can be a very *large* difference
                            in potential between the two devices in the event of a lightning strike.

                            I am not familiar with audio equipment, but I seem to recall something
                            called a "Pin 1" problem with XLR connectors and "ground", IIRC.

                            FWIW, I have seen an instance where the neutral wire from the pole was
                            not exactly at "ground" potential, as measured by an electrician...

                            Randy

                            On 3/1/2012 9:08 AM, Ron Wright, N9EE wrote:
                            >
                            > Ground is a central point hopefully common to all gear in a system. It
                            > could be say 4000 V difference between what is ground 3 blocks away.
                            >
                            > However, some equipment that has say plastic enclosures where one
                            > cannot come in contact with any metal or electrical parts the ground
                            > for this piece of equipment would have its own ground inside and not
                            > connected to other equipment grounds. TVs are one example.
                            >
                            > Ground is a zero voltage point, but may be zero to that piece of gear
                            > and may be at a different voltage to another piece of equipment ground.
                            >
                            > We should not get into RF grounds here for they are much more complex,
                            > but for safety equipment where the operators can come in contact with
                            > metal and possible electrical voltages these metals are "gounded",
                            > that is connected with physical metal or wires together so they will
                            > be at the same voltage, zero for reference.
                            >
                            > We typically like to bring all these grounds to Earth ground, the
                            > actual dirt around the equipment.
                            >
                            > With your equipment that has either a 2 prong AC plug or wal-wart the
                            > chassis are covered and not exposed. However, when connecting them
                            > together there needs to be a reference for the signals to work
                            > together, but this does not have to be the safety ground of a chassis,
                            > but must have some sort of reference point.
                            >
                            > I think you are trying to get a safety or common ground on your
                            > equipment. Often this will only be thru the interconnecting cables,
                            > but if want a safety ground then the chassis's or power supply grounds
                            > would need to be connected.
                            >
                            > Ground is a zero voltage point, but might be at different voltages for
                            > different pieces of gear. I've seen PCs get grounded to other
                            > equipment and the PC would shut down. Why, its ground did not like
                            > being grounded to Earth ground or other equipment grounds. This was in
                            > the design.
                            >
                            > In most equipment ground is the zero voltage point all other voltages
                            > operate in reference to so the gear can function, but these grounds
                            > might not be at other equipment grounds; different voltage. Again has
                            > to be in the design.
                            >
                            > 73, ron, n9ee/r
                            >
                            > --- In Electronics_101@yahoogroups.com
                            > <mailto:Electronics_101%40yahoogroups.com>, "David" <dalbamonte@...>
                            > wrote:
                            > >
                            > > I have never been able to get my head around floating ground. I know
                            > it is ground relative to a signal, but how does that affect safety?
                            > >
                            > > I have three pieces of equipment I want to hook together.
                            > >
                            > > One is a late 50'/early 60's Hammond Organ. I know the chassis is
                            > floating ground because it is 2 wire mains.
                            > >
                            > > The second is a behringer mixer which has a three pin cord for the
                            > wall and a weird connecter on the mixer itself. I assumed that signal
                            > ground on this would be earth ground.
                            > >
                            > > The third is a keyboard which runs off a wall wart. I dont know
                            > exactly why I am not concerned about the ground on this, but I am not.
                            > I guess in reality I am not worried about it being compatible with the
                            > mixer.
                            > >
                            > > The hammond has a rca in. I want to come out of the mixer effects
                            > out and into the rca in. This will let me run my wall wart keyboard
                            > through the leslie. I know the pin on the leslie is connected to a
                            > capacitor which should isolate it from the dc operating voltage in the
                            > tube amp on the Hammond. I also know that if the capacitor is bad it
                            > will mess with the operating voltage on the Hammond and possibly not
                            > be as loud. So i want to test the dc voltage on the pin on the rca.
                            > But I am not comfortable about how the grounds would work so I checked
                            > with a volt meter. I figured the Bheringer would ground the Hammond
                            > through the ground on the signal cable if the difference was not too
                            > great. I measured the voltage between the ground on the Behringer and
                            > the Hammond. I was checking DC voltage and it was all over the place,
                            > but seemed to be less than 150mV. Then I checked the ac voltage.
                            > Between the behringer and the Hammond there was close to 18V AC. But
                            > when I disconnected the hammond the ac was still high. I put the lead
                            > on a screw on the switch plate (assumed ground) and got 26 V AC. Now I
                            > am really puzzled.
                            > >
                            > > When is ground, ground? And how can I be sure I can hook these
                            > things up without frying something?
                            > >
                            >
                            >
                            >
                            > No virus found in this message.
                            > Checked by AVG - www.avg.com <http://www.avg.com>
                            > Version: 2012.0.1913 / Virus Database: 2114/4842 - Release Date: 02/29/12
                            >



                            [Non-text portions of this message have been removed]
                          • David
                            Oh, I like it. Thats what I need simple tests for simple folk. (In addition to the good explanations previously received regarding ground.) I do think you
                            Message 13 of 27 , Mar 2, 2012
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                              Oh, I like it. Thats what I need simple tests for simple folk. (In addition to the good explanations previously received regarding ground.)

                              I do think you missed that I was going to connect the effects send out of the mixer to the organ. The output of the organ is to a speaker. I think it is in the 8 to 12 watts range. There will be no effects return from this. But I understand what you are saying and thank you for it.

                              David

                              > I can't add anything to what has been previously said about "What is
                              > ground?". However, you can make some easy checks with a volt meter's
                              > ohm scale to see if it is safe to connect the organ and keyboard to the
                              > mixer. Measure the resistance between each pin on the Hammond Organ's
                              > output connector and each pin on the AC power plug. It should be
                              > infinite. Repeat the same test with input pins of the mixer and its AC
                              > power plug. Repeat the same test with the output pins of the keyboard
                              > and its
                              > AC power plug.
                              >
                              > If all the readings are infinite than is is safe to connect the organ
                              > and keyboard to the mixer.
                              > If only the mixer shows a low resistance between its AC power plug's
                              > ground pin and one or more of its input pins than it is safe to connect
                              > the organ and keyboard to the mixer.
                              >
                              > Howard.
                              >
                              >
                              > [Non-text portions of this message have been removed]
                              >
                            • David
                              You are the second to mention isolation transformers, but in context of my example it is unclear if you are suggesting isloation of the input / output of the
                              Message 14 of 27 , Mar 2, 2012
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                                You are the second to mention isolation transformers, but in context of my example it is unclear if you are suggesting isloation of the input / output of the indivual devices or isolation of the power supply.

                                --- In Electronics_101@yahoogroups.com, Kirk McLoren <kirkmcloren@...> wrote:
                                >
                                > thus the use of isolation transformers
                                >
                                > Nemo dat quod non habet
                                >
                                gratias multum amicus
                              • Kirk McLoren
                                isolation of the power supply Nemo dat quod non habet ________________________________ From: David To: Electronics_101@yahoogroups.com
                                Message 15 of 27 , Mar 2, 2012
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                                  isolation of the power supply



                                  Nemo dat quod non habet


                                  ________________________________
                                  From: David <dalbamonte@...>
                                  To: Electronics_101@yahoogroups.com
                                  Sent: Friday, March 2, 2012 9:46 AM
                                  Subject: [Electronics_101] Re: When is ground ground?



                                   

                                  You are the second to mention isolation transformers, but in context of my example it is unclear if you are suggesting isloation of the input / output of the indivual devices or isolation of the power supply.

                                  --- In Electronics_101@yahoogroups.com, Kirk McLoren <kirkmcloren@...> wrote:
                                  >
                                  > thus the use of isolation transformers
                                  >
                                  > Nemo dat quod non habet
                                  >
                                  gratias multum amicus




                                  [Non-text portions of this message have been removed]
                                • David
                                  Thank you all for your advice. I checked the impedance from the pins of inputs and outputs. I checked the voltage pin to pin. There is about .16V DC leakage
                                  Message 16 of 27 , Mar 2, 2012
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                                    Thank you all for your advice. I checked the impedance from the pins of inputs and outputs. I checked the voltage pin to pin. There is about .16V DC leakage from the Hammond. I understand that is within the normal range, but I dont know if it will fry the mixer's FX out. I tried it anyway. Sounds way cool. Hope it is ok long term. I got the keyboard to sound like "Blue Jay Way." Thanks again.

                                    --- In Electronics_101@yahoogroups.com, "David" <dalbamonte@...> wrote:
                                    >
                                    > I have never been able to get my head around floating ground. I know it is ground relative to a signal, but how does that affect safety?
                                    >
                                    > I have three pieces of equipment I want to hook together.
                                    >
                                    > One is a late 50'/early 60's Hammond Organ. I know the chassis is floating ground because it is 2 wire mains.
                                    >
                                    > The second is a behringer mixer which has a three pin cord for the wall and a weird connecter on the mixer itself. I assumed that signal ground on this would be earth ground.
                                    >
                                    > The third is a keyboard which runs off a wall wart. I dont know exactly why I am not concerned about the ground on this, but I am not. I guess in reality I am not worried about it being compatible with the mixer.
                                    >
                                    > The hammond has a rca in. I want to come out of the mixer effects out and into the rca in. This will let me run my wall wart keyboard through the leslie. I know the pin on the leslie is connected to a capacitor which should isolate it from the dc operating voltage in the tube amp on the Hammond. I also know that if the capacitor is bad it will mess with the operating voltage on the Hammond and possibly not be as loud. So i want to test the dc voltage on the pin on the rca. But I am not comfortable about how the grounds would work so I checked with a volt meter. I figured the Bheringer would ground the Hammond through the ground on the signal cable if the difference was not too great. I measured the voltage between the ground on the Behringer and the Hammond. I was checking DC voltage and it was all over the place, but seemed to be less than 150mV. Then I checked the ac voltage. Between the behringer and the Hammond there was close to 18V AC. But when I disconnected the hammond the ac was still high. I put the lead on a screw on the switch plate (assumed ground) and got 26 V AC. Now I am really puzzled.
                                    >
                                    > When is ground, ground? And how can I be sure I can hook these things up without frying something?
                                    >
                                  • James M. Geidl
                                    Good job!! I know I am going to take heat for this but I firmly believe that half of electronics is, Oh crap, just plug it in! James M. Geidl, K6JMG D.B.
                                    Message 17 of 27 , Mar 2, 2012
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                                      Good job!!

                                      I know I am going to take heat for this but I firmly believe that half of
                                      electronics is, "Oh crap, just plug it in!"

                                      James M. Geidl, K6JMG
                                      D.B. Cooper, you have a message.

                                      -----Original Message-----
                                      From: Electronics_101@yahoogroups.com
                                      [mailto:Electronics_101@yahoogroups.com] On Behalf Of David
                                      Sent: Friday, March 02, 2012 4:04 PM
                                      To: Electronics_101@yahoogroups.com
                                      Subject: [Electronics_101] Re: When is ground ground?

                                      Thank you all for your advice. I checked the impedance from the pins of
                                      inputs and outputs. I checked the voltage pin to pin. There is about .16V
                                      DC leakage from the Hammond. I understand that is within the normal range,
                                      but I dont know if it will fry the mixer's FX out. I tried it anyway.
                                      Sounds way cool. Hope it is ok long term. I got the keyboard to sound like
                                      "Blue Jay Way." Thanks again.

                                      --- In Electronics_101@yahoogroups.com, "David" <dalbamonte@...> wrote:
                                      >
                                      > I have never been able to get my head around floating ground. I know it
                                      is ground relative to a signal, but how does that affect safety?
                                      >
                                      > I have three pieces of equipment I want to hook together.
                                      >
                                      > One is a late 50'/early 60's Hammond Organ. I know the chassis is
                                      floating ground because it is 2 wire mains.
                                      >
                                      > The second is a behringer mixer which has a three pin cord for the wall
                                      and a weird connecter on the mixer itself. I assumed that signal ground on
                                      this would be earth ground.
                                      >
                                      > The third is a keyboard which runs off a wall wart. I dont know exactly
                                      why I am not concerned about the ground on this, but I am not. I guess in
                                      reality I am not worried about it being compatible with the mixer.
                                      >
                                      > The hammond has a rca in. I want to come out of the mixer effects out and
                                      into the rca in. This will let me run my wall wart keyboard through the
                                      leslie. I know the pin on the leslie is connected to a capacitor which
                                      should isolate it from the dc operating voltage in the tube amp on the
                                      Hammond. I also know that if the capacitor is bad it will mess with the
                                      operating voltage on the Hammond and possibly not be as loud. So i want to
                                      test the dc voltage on the pin on the rca. But I am not comfortable about
                                      how the grounds would work so I checked with a volt meter. I figured the
                                      Bheringer would ground the Hammond through the ground on the signal cable if
                                      the difference was not too great. I measured the voltage between the ground
                                      on the Behringer and the Hammond. I was checking DC voltage and it was all
                                      over the place, but seemed to be less than 150mV. Then I checked the ac
                                      voltage. Between the behringer and the Hammond there was close to 18V AC.
                                      But when I disconnected the hammond the ac was still high. I put the lead
                                      on a screw on the switch plate (assumed ground) and got 26 V AC. Now I am
                                      really puzzled.
                                      >
                                      > When is ground, ground? And how can I be sure I can hook these things up
                                      without frying something?
                                      >




                                      ------------------------------------

                                      Please trim excess when replyingYahoo! Groups Links
                                    • Donald H Locker
                                      The worst that could have happened is something blows up; eventually you ve got to try it. Sounds like you did the checks, plugged it in and it worked.
                                      Message 18 of 27 , Mar 2, 2012
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                                        The worst that could have happened is something blows up; eventually you've got to try it. Sounds like you did the checks, plugged it in and it worked. Congratulations.

                                        Donald.
                                        --
                                        *Plain Text* email -- it's an accessibility issue
                                        () no proprietary attachments; no html mail
                                        /\ ascii ribbon campaign - <www.asciiribbon.org>

                                        ----- Original Message -----
                                        > From: "David" <dalbamonte@...>
                                        > To: "Electronics 101" <Electronics_101@yahoogroups.com>
                                        > Sent: Friday, March 2, 2012 7:03:31 PM
                                        > Subject: [Electronics_101] Re: When is ground ground?
                                        > Thank you all for your advice. I checked the impedance from the pins
                                        > of inputs and outputs. I checked the voltage pin to pin. There is
                                        > about .16V DC leakage from the Hammond. I understand that is within
                                        > the normal range, but I dont know if it will fry the mixer's FX out. I
                                        > tried it anyway. Sounds way cool. Hope it is ok long term. I got the
                                        > keyboard to sound like "Blue Jay Way." Thanks again.
                                        >
                                        > --- In Electronics_101@yahoogroups.com, "David" <dalbamonte@...>
                                        > wrote:
                                        > >
                                        > > I have never been able to get my head around floating ground. I know
                                        > > it is ground relative to a signal, but how does that affect safety?
                                        > >
                                        > > I have three pieces of equipment I want to hook together.
                                        > >
                                        > > One is a late 50'/early 60's Hammond Organ. I know the chassis is
                                        > > floating ground because it is 2 wire mains.
                                        > >
                                        > > The second is a behringer mixer which has a three pin cord for the
                                        > > wall and a weird connecter on the mixer itself. I assumed that
                                        > > signal ground on this would be earth ground.
                                        > >
                                        > > The third is a keyboard which runs off a wall wart. I dont know
                                        > > exactly why I am not concerned about the ground on this, but I am
                                        > > not. I guess in reality I am not worried about it being compatible
                                        > > with the mixer.
                                        > >
                                        > > The hammond has a rca in. I want to come out of the mixer effects
                                        > > out and into the rca in. This will let me run my wall wart keyboard
                                        > > through the leslie. I know the pin on the leslie is connected to a
                                        > > capacitor which should isolate it from the dc operating voltage in
                                        > > the tube amp on the Hammond. I also know that if the capacitor is
                                        > > bad it will mess with the operating voltage on the Hammond and
                                        > > possibly not be as loud. So i want to test the dc voltage on the pin
                                        > > on the rca. But I am not comfortable about how the grounds would
                                        > > work so I checked with a volt meter. I figured the Bheringer would
                                        > > ground the Hammond through the ground on the signal cable if the
                                        > > difference was not too great. I measured the voltage between the
                                        > > ground on the Behringer and the Hammond. I was checking DC voltage
                                        > > and it was all over the place, but seemed to be less than 150mV.
                                        > > Then I checked the ac voltage. Between the behringer and the Hammond
                                        > > there was close to 18V AC. But when I disconnected the hammond the
                                        > > ac was still high. I put the lead on a screw on the switch plate
                                        > > (assumed ground) and got 26 V AC. Now I am really puzzled.
                                        > >
                                        > > When is ground, ground? And how can I be sure I can hook these
                                        > > things up without frying something?
                                        > >
                                        >
                                        >
                                        >
                                        >
                                        > ------------------------------------
                                        >
                                        > Please trim excess when replyingYahoo! Groups Links
                                        >
                                        >
                                        >
                                      • Ross McKenzie
                                        And the other half is Just plug it in ... oh crap!
                                        Message 19 of 27 , Mar 2, 2012
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                                          And the other half is "Just plug it in ... oh crap!"


                                          On 3/03/2012 10:17 AM, James M. Geidl wrote:
                                          > Good job!!
                                          >
                                          > I know I am going to take heat for this but I firmly believe that half of
                                          > electronics is, "Oh crap, just plug it in!"
                                          >
                                          > James M. Geidl, K6JMG
                                          >
                                        • David
                                          Thanks. Sounds cool.
                                          Message 20 of 27 , Mar 3, 2012
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                                            Thanks. Sounds cool.

                                            --- In Electronics_101@yahoogroups.com, Donald H Locker <dhlocker@...> wrote:
                                            >
                                            > The worst that could have happened is something blows up; eventually you've got to try it. Sounds like you did the checks, plugged it in and it worked. Congratulations.
                                            >
                                            > Donald.
                                            > --
                                          • David
                                            So I isolate the power supply on one and let the signal grounds take care of themselves?
                                            Message 21 of 27 , Mar 3, 2012
                                            • 0 Attachment
                                              So I isolate the power supply on one and let the signal grounds take care of themselves?

                                              --- In Electronics_101@yahoogroups.com, Kirk McLoren <kirkmcloren@...> wrote:
                                              >
                                              > isolation of the power supply
                                              >
                                              >
                                              >
                                              > Nemo dat quod non habet
                                              >
                                              >
                                            • Kirk McLoren
                                              I would isolate all of them on the same transformer is ok I once got a nasty shock by touching a mounting screw on the bottom of a plastic radio enclosure Nemo
                                              Message 22 of 27 , Mar 3, 2012
                                              • 0 Attachment
                                                I would isolate all of them
                                                on the same transformer is ok
                                                I once got a nasty shock by touching a mounting screw on the bottom of a plastic radio enclosure


                                                Nemo dat quod non habet


                                                ________________________________
                                                From: David <dalbamonte@...>
                                                To: Electronics_101@yahoogroups.com
                                                Sent: Saturday, March 3, 2012 4:55 AM
                                                Subject: [Electronics_101] Re: When is ground ground?



                                                 

                                                So I isolate the power supply on one and let the signal grounds take care of themselves?

                                                --- In Electronics_101@yahoogroups.com, Kirk McLoren <kirkmcloren@...> wrote:
                                                >
                                                > isolation of the power supply
                                                >
                                                >
                                                >
                                                > Nemo dat quod non habet
                                                >
                                                >




                                                [Non-text portions of this message have been removed]
                                              • ae5ew
                                                Consumer radio products should be double insulated so you shouldn t get shocked by them. Older consumer radios with non-polarized plugs used to permit the
                                                Message 23 of 27 , Mar 4, 2012
                                                • 0 Attachment
                                                  Consumer radio products should be double insulated so you shouldn't get shocked by them. Older consumer radios with non-polarized plugs used to permit the 'chassis' to go hot. Polarized plugs prevent that. Double insulation certainly helps prevent internal equipment failure from shocking people. Third-wire (green, grounds) also prevent electrical shocks.

                                                  I would tie one side of each output to a good chassis ground. For a bridge rectifier, this would be after the rectifier. For separate circuits designed for balanced outputs, I wouldn't tie any to a common ground. Output transformers provide a balanced output also (if desired). The application circuit actually dictates the best design implementation.

                                                  Charles AE5EW

                                                  --- In Electronics_101@yahoogroups.com, Kirk McLoren <kirkmcloren@...> wrote:
                                                  >
                                                  > I would isolate all of them
                                                  > on the same transformer is ok
                                                  > I once got a nasty shock by touching a mounting screw on the bottom of a plastic radio enclosure
                                                  >
                                                  >
                                                  > Nemo dat quod non habet
                                                  >
                                                  >
                                                  > ________________________________
                                                  > From: David <dalbamonte@...>
                                                  > To: Electronics_101@yahoogroups.com
                                                  > Sent: Saturday, March 3, 2012 4:55 AM
                                                  > Subject: [Electronics_101] Re: When is ground ground?
                                                  >
                                                  >
                                                  >
                                                  >  
                                                  >
                                                  > So I isolate the power supply on one and let the signal grounds take care of themselves?
                                                  >
                                                  > --- In Electronics_101@yahoogroups.com, Kirk McLoren <kirkmcloren@> wrote:
                                                  > >
                                                  > > isolation of the power supply
                                                  > >
                                                  > >
                                                  > >
                                                  > > Nemo dat quod non habet
                                                  > >
                                                  > >
                                                  >
                                                  >
                                                  >
                                                  >
                                                  > [Non-text portions of this message have been removed]
                                                  >
                                                • Kirk McLoren
                                                  should be but werent dont know if anything has been done about it but the one that bit me was legal Nemo dat quod non habet ________________________________
                                                  Message 24 of 27 , Mar 4, 2012
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                                                    should be but werent
                                                    dont know if anything has been done about it but the one that bit me was legal


                                                    Nemo dat quod non habet


                                                    ________________________________
                                                    From: ae5ew <ae5ew.us@...>
                                                    To: Electronics_101@yahoogroups.com
                                                    Sent: Sunday, March 4, 2012 5:17 AM
                                                    Subject: [Electronics_101] Re: When is ground ground?



                                                     

                                                    Consumer radio products should be double insulated so you shouldn't get shocked by them. Older consumer radios with non-polarized plugs used to permit the 'chassis' to go hot. Polarized plugs prevent that. Double insulation certainly helps prevent internal equipment failure from shocking people. Third-wire (green, grounds) also prevent electrical shocks.

                                                    I would tie one side of each output to a good chassis ground. For a bridge rectifier, this would be after the rectifier. For separate circuits designed for balanced outputs, I wouldn't tie any to a common ground. Output transformers provide a balanced output also (if desired). The application circuit actually dictates the best design implementation.

                                                    Charles AE5EW

                                                    --- In Electronics_101@yahoogroups.com, Kirk McLoren <kirkmcloren@...> wrote:
                                                    >
                                                    > I would isolate all of them
                                                    > on the same transformer is ok
                                                    > I once got a nasty shock by touching a mounting screw on the bottom of a plastic radio enclosure
                                                    >
                                                    >
                                                    > Nemo dat quod non habet
                                                    >
                                                    >
                                                    > ________________________________
                                                    > From: David <dalbamonte@...>
                                                    > To: Electronics_101@yahoogroups.com
                                                    > Sent: Saturday, March 3, 2012 4:55 AM
                                                    > Subject: [Electronics_101] Re: When is ground ground?
                                                    >
                                                    >
                                                    >
                                                    >  
                                                    >
                                                    > So I isolate the power supply on one and let the signal grounds take care of themselves?
                                                    >
                                                    > --- In Electronics_101@yahoogroups.com, Kirk McLoren <kirkmcloren@> wrote:
                                                    > >
                                                    > > isolation of the power supply
                                                    > >
                                                    > >
                                                    > >
                                                    > > Nemo dat quod non habet
                                                    > >
                                                    > >
                                                    >
                                                    >
                                                    >
                                                    >
                                                    > [Non-text portions of this message have been removed]
                                                    >




                                                    [Non-text portions of this message have been removed]
                                                  • Donald H Locker
                                                    Besides checking voltage between two pieces of equipment, also check the current. It is possible for two pieces of unconnected and floating (with respect to
                                                    Message 25 of 27 , Mar 14, 2012
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                                                      Besides checking voltage between two pieces of equipment, also check the current. It is possible for two pieces of unconnected and floating (with respect to earth) equipment to many volts different, but have essentially no leakage such that they can be safely connected together and to earth. If the current between the two is less than a few milliamps, connecting them together should be safe. If more, some research into why they so want to exchange charge is in order.

                                                      Donald.
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                                                      ----- Original Message -----
                                                      > From: "David" <dalbamonte@...>
                                                      > To: "Electronics 101" <Electronics_101@yahoogroups.com>
                                                      > Sent: Thursday, March 1, 2012 1:23:23 PM
                                                      > Subject: [Electronics_101] Re: When is ground ground?
                                                      > --- In Electronics_101@yahoogroups.com, "Ron Wright, N9EE"
                                                      > <mccrpt@...> wrote:
                                                      > >
                                                      > [snip]
                                                      > >
                                                      > > However, some equipment that has say plastic enclosures where one
                                                      > > cannot come in contact with any metal or electrical parts the ground
                                                      > > for this piece of equipment would have its own ground inside and not
                                                      > > connected to other equipment grounds. TVs are one example.
                                                      > >
                                                      > The keyboard in my example is another. That is one of the reasons I am
                                                      > not worried about it.
                                                      >
                                                      > > Ground is a zero voltage point, but may be zero to that piece of
                                                      > > gear and may be at a different voltage to another piece of equipment
                                                      > > ground.
                                                      > >
                                                      > That is one of the things I am concened about. In this case the
                                                      > connection of a peice of tube gear to IC gear. The tube stuff seems
                                                      > like it works by modulating an applied high DC voltage. The use
                                                      > capacitance coupling to keep one part of the circuite from interfering
                                                      > with the voltage requirements of the nexts stage.
                                                      >
                                                      > > We should not get into RF grounds here for they are much more
                                                      > > complex, but for safety equipment where the operators can come in
                                                      > > contact with metal and possible electrical voltages these metals are
                                                      > > "gounded", that is connected with physical metal or wires together
                                                      > > so they will be at the same voltage, zero for reference.
                                                      > >
                                                      > > We typically like to bring all these grounds to Earth ground, the
                                                      > > actual dirt around the equipment.
                                                      > >
                                                      > > With your equipment that has either a 2 prong AC plug or wal-wart
                                                      > > the chassis are covered and not exposed. However, when connecting
                                                      > > them together there needs to be a reference for the signals to work
                                                      > > together, but this does not have to be the safety ground of a
                                                      > > chassis, but must have some sort of reference point.
                                                      > >
                                                      >
                                                      > > I think you are trying to get a safety or common ground on your
                                                      > > equipment. Often this will only be thru the interconnecting cables,
                                                      > > but if want a safety ground then the chassis's or power supply
                                                      > > grounds would need to be connected.
                                                      > >
                                                      > Yes. I would like a safety ground. When interconnecting multiple
                                                      > guitar amps the practice used to be to disconnect the ground on the
                                                      > plug on all but one amplifier. Then the common ground is made by the
                                                      > shield on the interconnected guitar cables. I was thinking the mixer
                                                      > would be ground and then the cable would provide ground. I was stopped
                                                      > in step one when I found the shield on the mixer to be 26V (18VAC to
                                                      > the hammond). The hammond was plugged in but not turned on during this
                                                      > test.
                                                      >
                                                      > My plan was. Fire up the mixer, test to ground on the hammond. Then if
                                                      > I wasnt too unhappy with the results, fire up the hammond and check
                                                      > again. Then I was going to check tip to tip for dc voltage. I was
                                                      > stopped at step one.
                                                      >
                                                      > > Ground is a zero voltage point, but might be at different voltages
                                                      > > for different pieces of gear. I've seen PCs get grounded to other
                                                      > > equipment and the PC would shut down. Why, its ground did not like
                                                      > > being grounded to Earth ground or other equipment grounds. This was
                                                      > > in the design.
                                                      > >
                                                      > > In most equipment ground is the zero voltage point all other
                                                      > > voltages operate in reference to so the gear can function, but these
                                                      > > grounds might not be at other equipment grounds; different voltage.
                                                      > > Again has to be in the design.
                                                      > >
                                                      >
                                                      > The hammond has an RCA input which I was hoping would provide the
                                                      > common ground, but I do not know what the limitation are regarding the
                                                      > different ground point.
                                                      >
                                                      > David
                                                      >
                                                      >
                                                      >
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