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RE: [regsaudioforum] hum

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  • Ted Rook
    Eric and Tom, I think your thought is bang on Tom, I have had the same experience a thousand times while checking crosstalk in mixers, always worse around
    Message 1 of 42 , Jun 1, 2006
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      Eric and Tom,

      I think your thought is bang on Tom, I have had the same experience a thousand times
      while checking crosstalk in mixers, always worse around midtravel of the pot because
      the moving contact (wiper) then has its maximum impedance to ground.

      At full-off the wiper circuit is at a very low impedance (a few Ohms) similarly at full travel
      it is at the lowish impedance of the driving stage (a few tens of Ohms or maybe less than
      an Ohm).

      In between full and off the impedance at the wiper reaches a maximum which is 25% of
      the pot total resistance value, because the wiper has two parallel connections, one
      towards the ground and one towards the source and these are in parallel.

      So with a 100k volume pot the wiper has a maximum impedance to ground at 50% travel
      of 25k (50k in parallel with 50k). This is not important in a mono circuit or where there
      are no interfering signals nearby.

      But an audio amp, lets say a stereo preamp, has a mains transformer humming at 60Hz
      and 120Hz, possibly digital logic clocks in a display and/or remote circuit injecting noise
      into the audio.

      In the case of a stereo preamp there is also the other channel as a source of crosstalk.
      All these leak into the audio circuit and the leakage is proportional to the impedance. If
      the impedance is very low the crosstalk ratio will be very low. If the impedance is very
      high so will be the crosstalk ratio and noise pickup.

      In a well designed preamp these factors are considered during design and no
      objectionable noises will be apparent at mid volume settings. In a less careful design
      there may be slight, moderate or severe noise reception at mid pot settings.

      This is just physics, nothing to do with how the pot is made or even how well it is made.
      Some shielding around the pot in the form of a metal case might mitigate sensitivity to
      external noise but even this would not help with stereo crosstalk between the left and
      right channels of the pot. And thin metal cases are not particulalrly good hum shields.


      Turning to practical matters the first approach, because it costs nothing, is to move the
      offending object, the unit with a power transformmer in it is probably the culprit, move
      them apart. Play around with the physical orientation of the "radiator" and "receiver"
      while listening to both channels. Tune the orientation for least hum.

      If that doesn't work post again and I will see if I can be more help.

      Ted


      On 1 Jun 2006 at 11:58, Tom Mallin wrote:

      >
      > I don't pretend to have the expertise to diagnose or solve such a problem, Eric, but from what
      > you describe, the problem could relate to the variable output impedance of your passive preamp
      > at various positions of its volume control. Unlike active line stages, the output impedance of
      > most passive units varies considerably withthe potentiometer setting, and their output
      > impedance does not change linearly with the setting of the volume control.Just a thought.
      >
      >
      >
      > >>> eweitzman@... 06/01/06 11:23AM >>>
      > Tom wrote,
      >
      > > Thanks for citing the Jensen paper, Eric. I was going to refer
      > > everyone to that as well. That's the paper Linkwitz refers
      > > desperate Orion users to.
      >
      > I didn't know Linkwitz had a link to this paper.
      >
      > > I'm not the only one who has seemingly unique hum problems once
      > > the Orion EQ/crossover box and its power supply are connected to
      > > a system.
      >
      > I've had a weird hum problem ever since I bought a Yamaha C2a to use as a
      > phono preamp four years ago. It causes hum when I use my passive preamp only
      > at certain high level settings -- but not at full volume. Strange problem.
      > There's no hum with an active preamp in the system. Changing the plug
      > orientation changed things without helping: One way, the system hummed with
      > the Yamaha off, the other way, it hummed with the Yamaha on. I had a choice
      > between humming LPs or humming CDs. :(
      >
      > - Eric
      >
      >
      >
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    • Ted Rook
      Richard I have never bothered about turning electronics on or off consistently. It is the different rates of themal expansion among the materials that make up
      Message 42 of 42 , Jun 6, 2006
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        Richard

        I have never bothered about turning electronics on or off consistently.

        It is the different rates of themal expansion among the materials that make up
        electronics that give rise to thermal cycling stresses. For example deep inside IC chips
        are tiny little wires that flex a bit with every thermal cycle. They do not have infinite life
        expectancy.

        The other factor is the finite operating life of components. Generally low stress parts
        (that run cool) have long and very long lives. Whereas parts that are stressed (run hot)
        have shorter lives.
        The semiconductor devices that are now everywhere are so reliable because they run
        cool and we have been making them for so long now that most of the manufacturing
        flaws have been found and fixed.

        Tubes are another matter, the opposite extreme. Hot power devices in power amps
        possess both properties, they are subjected to thermal aging when cycled hot cold, and,
        they have finite lives because they operate hot. Damned if you do and damned if you
        don't. Probably best on balance to turn stuff on when you need it and off when you don't.

        Thames Valley huh? For some reason I had you up North, something to do with the old
        firm I think. I am also an adopter of compact fluorescent lights, I went for 100 Watters in
        a big way, just one snag, they mess up AM reception a bit.

        Thanks for the mic tips.

        Ted


        On 6 Jun 2006 at 15:17, Richard Tuck wrote:

        >
        > Hi Ted
        >
        > Following the discovery of just how much electricity we were using ( CO2 wise probably offset by
        > my zero length commute) we decided to look at way of economising -a bit for the planet, a bit
        > forour pockets. Having exhusted the low energy lamp thing we started looking elsewhere.
        > BTWthere are substitutes for virtually every lamptype now, including minature spots and
        > floods. Because of the diffuse source they do not have the throw of of a Q H lamp but in most
        > places and they work just fine and e.g. 50W goes to 11W.
        >
        > I bought a new toy:
        >
        > http://www.maplin.co.uk/Search.aspx?criteria=watt%20meter&doy=6m6&source=15
        >
        > Really usefully it integrates and reads out kW hrs.
        >
        > Looks very useful and I'm sure there are US equivalents. At the moment it thinks the voltage is
        > 241.4V and f=49.9 Hz. Robert reports the weather in Brussels, I report the mains conditions in
        > the Thames Valley.
        >
        > On this topic what is the collective view of leaving solid state amps permanently on so they are
        > warm? Maybe a timer to turn them off during the night might save a bit? We could start a new
        > Green Audio movement.
        >
        > Thoughts from all please?
        >
        > Richard
        >
        >
        > From: regsaudioforum@yahoogroups.com [mailto:regsaudioforum@yahoogroups.com] On
        > Behalf Of Richard Tuck
        > Sent: 02 June 2006 21:18
        > To: regsaudioforum@yahoogroups.com
        > Subject: RE: [regsaudioforum] Re: "Audiophile" Power Cords
        >
        > Hi Ted
        >
        > Just for you actual at 2216 hours is237V +/- the uncertainty of my meter which has never been
        > calibrated.
        >
        > Richard
        >
        >
        > From: regsaudioforum@yahoogroups.com [mailto:regsaudioforum@yahoogroups.com] On
        > Behalf Of Ted Rook
        > Sent: 02 June 2006 21:04
        > To: regsaudioforum@yahoogroups.com
        > Subject: RE: [regsaudioforum] Re: "Audiophile" Power Cords
        >
        > Thank you Richard, my information is that the spec is 230V +/- 10% rather than +/- 10V.
        > My curiosity is to see where we have got to with the 240 to 230 changeover. I suspect
        > you are still getting 240V from the street and I wanted to have an actual reading.
        >
        > Ted
        >
        > On 2 Jun 2006 at 16:16, Richard Tuck wrote:
        >
        > >
        > > Hi Ted
        > >
        > > Current spec is 230 +/- 10V.
        > >
        > > Richard
        > >
        > >
        > > From: regsaudioforum@yahoogroups.com [mailto:regsaudioforum@yahoogroups.com] On
        > > Behalf Of Ted Rook
        > > Sent: 02 June 2006 04:25
        > > To: regsaudioforum@yahoogroups.com
        > > Subject: RE: [regsaudioforum] Re: "Audiophile" Power Cords
        > >
        > > Richard, can you please satisfy my curiosity next time your multimeter is in hand and
        > > give an exact (range of) voltage reading for your house power?
        > >
        > > Thanks
        > >
        > > Ted
        > >
        > > On 1 Jun 2006 at 22:15, Richard Tuck wrote:
        > >
        > > >
        > > > Hi Tom
        > > >
        > > > Is the 110V thing that makes you guys in the US so sloppy with earthing. Proper earthing has
        > > > been mandatory on power socketsin the UK since, well almostforever. A little after that it
        > > > became mandatory in all lighting circuits. I still find occasional light fittings that need earths
        > in
        > > > my mid 1930s house but never non-earthed power sockets. Is your mains balanced about
        > > earth
        > > > or is one wire neutral.
        > > >
        > > > In the UK 230V unbalanced gives you a healthy respect for mains. The standard UK system
        > is
        > > > called a ring main see http://en.wikipedia.org/wiki/Ring_circuit
        > > > it will intrigue you but actually is very good. Within reason you can add extra sockets and the
        > > > odd spur off the ring to another socket. It's so good most countries chose to go another way.
        > > > Only grouch is the plugs are rather big.
        > > >
        > > > Richard
        > > >
        > > >
        > > > From: regsaudioforum@yahoogroups.com [mailto:regsaudioforum@yahoogroups.com] On
        > > > Behalf Of rzangpo2
        > > > Sent: 01 June 2006 20:50
        > > > To: regsaudioforum@yahoogroups.com
        > > > Subject: [regsaudioforum] Re: "Audiophile" Power Cords
        > > >
        > > > You evidently know more about this than I do, Tom. My house was built
        > > > in 1970. I can only assume that the local building code didn't require
        > > > residential wiring to be grounded in those days.
        > > >
        > > > Ron Stiskin
        > > > New York
        > > >
        > > > --- In regsaudioforum@yahoogroups.com, "Tom Mallin" <tmallin@...> wrote:
        > > > >
        > > > > Electrical and other building codes are not uniform in the United
        > > > > States. There are some 44,000 jurisdictions (states, counties, cities,
        > > > > townships, etc.) with building code making authority in this country.
        > > > > You can imagine how tough this makes the job of insurance adjustment
        > > > > when a decision has to be made as to what the relevant building codes
        > > > > actually requires for a repair made at a particular location. Sorting
        > > > > that out is one of the types of information my company helps insurers
        > > > > with.
        > > > >
        > > > > Many US building codes allow earth grounding through the metal conduit
        > > > > which is connected to the metal outlet box. I happen to live in a county
        > > > > which requires this sort of grounding. The grounding screw on the
        > > > > outlet can be connected by wire to a screw screwed to the outlet box.
        > > > >
        > > > > But only spec and hospital grade electrical outlets have separate
        > > > > grounding screws. Cheaper outlets, which are used in much modern new
        > > > > dwelling construction and which are code compliant, rely on the mounting
        > > > > hardware for the outlet to make contact with the metal electrical box.
        > > > >
        > > > > In the next county to my west, metal outlet boxes are not permitted;
        > > > > plastic outlet boxes are required and all earth grounding is to be done
        > > > > through a third wire run from the outlet's grounding screw back to the
        > > > > ground buss in the electrical service box. Obviously, if you use a
        > >
        > > > > cheap grade of outlet in that type of installation, the third hole for
        > > > > the earth ground will truly be a "dummy."
        > > > >
        > > > > In my reference audio room, to stay within the applicable electrical
        > > > > code for my county, I had to use the metal outlet boxes, but I also run
        > > > > 10-gauge solid copper wires from the grounding screws of the
        > > > > hospital-grade outlets back to a single grounding screw in the
        > > > > electrical service box.
        > > > >
        > > > >
        > > > >
        > > > > >>> RZangpo2@... 06/01/06 06:37AM >>>
        > > > > Guys,
        > > > >
        > > > > I'm not having a problem with hum. I simply ran across this
        > > > > "scientific" explanation of how power cords might make a difference,
        > > > > and was curious whether there was anything to it. The answer seems to
        > > > > be, "not much".
        > > > >
        > > > > Ron Stiskin
        > > > > New York
        > > > >
        > > > > P.S. Like Ted's, my system is not grounded. Since my house has
        > > > > three-pronged outlets, I assumed the electrical service was grounded.
        > > > > I had owned the house for several years before I found out that it
        > > > > wasn't! The three-pronged outlets are dummies, as far as grounding is
        > > > > concerned.
        > > > >
        > > > > --- In regsaudioforum@yahoogroups.com, "Ted Rook" <rooknrol@>
        > > > > wrote:
        > > > > >
        > > > > > Ron and Robert:
        > > > > >
        > > > > > Good questions Robert.
        > > > > >
        > > > > > But the point about Audiophilia Nervosa is that it does not require
        > > > > the soil of a real
        > > > > > problem to flourish, it draws its nutrition from the life forces of
        > > > > the infected sufferer!!!!
        > > > > > and it is infectious and some makers of expensive products are the
        > > > > most contagious!!!!!
        > > > > >
        > > > > > I myself have experienced a bout this past two weeks and have
        > > > > escaped with the
        > > > > > expenditure of only $250 on some excellent used electronics, a
        > > > > matching DVD player for
        > > > > > my amp and (another) surround amp. I think the infection is subsiding
        > > > > :D
        > > > > >
        > > > > > I was going to attempt a thorough response but Tom's response is on
        > > > > the money and I
        > > > > > agree with everything he said, it is said as well as I could, (
        > > > > except the final paragraph
        > > > > > which doesn't affect the truth of what came before.)
        > > > > >
        > > > > > Robert's question is the vital one, is there a problem? Are you
        > > > > hearing clean audio?
        > > > > >
        > > > > > This "dialog" from Cardas opens with an undisclosed problem and is
        > > > > used as a way to
        > > > > > open a door into the mystical without ever declaring the nature of
        > > > > the problem.
        > > > > >
        > > > > > The first four sentences of the "answer" are gobbledegook without
        > > > > technical meaning.
        > > > > > They are meant to be said fast in a live situation to win the
        > > > > respect of the listener by
        > > > > > coercion, baffle them with science.
        > > > > >
        > > > > > Then sentence five says grounds are a problem. Not true. (I stopped
        > > > > reading here)
        > > > > > Grounds are not required for quiet clean hum free audio. My set up
        > > > > has been hum free
        > > > > > for six years without any ground connection at all. All the
        > > > > components have two
        > > > > > conductor power wires. All the connections are unbalanced RCA. No
        > > > > hum. No ground.
        > > > > > No hum. Audio does not require grounding for its operation. It may
        > > > > be desireable to
        > > > > > ground it for safety reasons but not to get hum free performance. In
        > > > > fact it is multiple
        > > > > > grounds that cause the infamous ground loop. If everything is
        > > > > grounded once and once
        > > > > > only there is no loop. It is unbalanced interconnects with the
        > > > > shield on at both ends
        > > > > > which create the loops when combined with multiple equipment chassis
        > > > > that are
        > > > > > grounded. But my system is all unbalanced and is hum free without a
        > > > > ground. Why?
        > > > > > because there are no powerful sources of line frequency magnetic
        > > > > radiation nearby to
        > > > > > induce hum into the system. And being ground free there can't be
        > > > > ground loops.
        > > > > >
        > > > > > I could go on but I won't it's late and I have to go to work
        > > > > tomorrow!
        > > > > > Just remember my system, no hum, no ground. It would work the same
        > > > > in your house
        > > > > > too unless you live next to power substation. And if you do then you
        > > > > have problems that
        > > > > > grounding won't help. There are several types of hum intereference
        > > > > and I'm afraid
        > > > > > Cardas is not about to educate us about what they are and how to fix
        > > > > them. I'm afraid
        > > > > > their advice is of "buy this" variety. And of course exposure to
        > > > > Audiophilia Nervosa.
        > > > > >
        > > > > > Did this help?
        > > > > >
        > > > > > Ted
        > > > > >
        > > > > >
        > > > > > On 1 Jun 2006 at 0:59, regtas43 wrote:
        > > > > >
        > > > > > > Are you hearing a lot of hum in your system?
        > > > > > > Otherwise what's the problem?
        > > > > > >
        > > > > > > Please note that things like the Bryston and McIntosh electronics
        > > > > > > deliver their extremely low nose and distortion figures on test
        > > > > with
        > > > > > > the suppplied power cords. Just exactly what is it one imagines
        > > > > > > might improve with a different cord?
        > > > > > >
        > > > > > > REG
        > > > > > >
        > > > > > > PS Cardas is a nice fellow but the Golden Ratio has nothing to do
        > > > > > > with audio, and this casts some doubt in my mind.....
        > > > > > >
        > > > > > > --- In regsaudioforum@yahoogroups.com, "rzangpo2" <RZangpo2@>
        > > > > > > wrote:
        > > > > > > >
        > > > > > > > I found this on the Cardas web site. I don't have the technical
        > > > > > > > knowledge to evaluate these statements. Anyone?
        > > > > > > >
        > > > > > > > Ron Stiskin
        > > > > > > > New York
        > > > > > > > __________
        > > > > > > >
        > > > > > > > Power Cords
        > > > > > > >
        > > > > > > > Q.) I've never tried changing the power cords and I'm pretty
        > > > > > > sceptical
        > > > > > > > about it. Could you please try to explain in engineering terms
        > > > > how
        > > > > > > > changing a power cord to a source component (CD player) which has
        > > > >
        > > > > > > an
        > > > > > > > internally regulated power supply, running in a fully balanced
        > > > > > > system
        > > > > > > > can change the sonic character of the system?
        > > > > > > >
        > > > > > > > I could understand if there were circulating ground currents
        > > > > > > between
        > > > > > > > the individual components in an unbalanced system, but in a
        > > > > > > balanced
        > > > > > > > system ground currents shouldn't be an issue unless the system
        > > > > had
        > > > > > > > insufficient common mode rejection or wasn't truely balanced in
        > > > > and
        > > > > > > > out. Thanks and regards, Sam F.
        > > > > > > >
        > > > > > > > A.) Sam, You are on the right track with the ground currents.
        > > > > Most
        > > > > > > > cords and power conditioners choke the line current which is
        > > > > > > useless
        > > > > > > > because the power supply almost always has a transformer on the
        > > > > > > input
        > > > > > > > that limits bandwidth quite well. Further slowing of the current
        > > > >
        > > > > > > input
        > > > > > > > is counter productive. Grounds on the other hand are a real
        > > > > issue.
        > > > > > > The
        > > > > > > > house ground is well too far away to provide any real ground as
        > > > > > > > related to RF or digital frequencies or sharp transients
        > > > > > > circulating
        > > > > > > > in the system. The wave length of these frequencies is far to
        > > > > > > short to
        > > > > > > > find a proper ground path so they find paths to circulate in the
        > > > > > > > system as a whole. This is a multi path condition that cannot be
        > > > > > > > common moded because it is the interaction of multiple path
        > > > > > > lengths,
        > > > > > > > like a ground loop, but at much higher frequency. This problem
        > > > > can
        > > > > > > be
        > > > > > > > so bad in shops and studios where there is a lot of digital
        > > > > > > equipment,
        > > > > > > > that the equipment actually malfunctions entirely. My chords have
        > > > > a
        > > > > > > > substantial cancellation of trans audio frequencies in the
        > > > > ground
        > > > > > > > plane, they are also effectively longer than the path to house
        > > > > > > ground
        > > > > > > > and in most cases this essentially stops the components from
        > > > > > > talking
        > > > > > > > to each other if they each have a cord.
        > > > > > > >
        > > > > > > > I did substantial testing using microphones and microphone power
        > > > > > > > supplies that are very sensitive to this problem. Replacing the
        > > > > > > power
        > > > > > > > cords is not a total solution but short of battery isolation it
        > > > > > > beats
        > > > > > > > most everything I have tried, short of lifting all the grounds,
        > > > > > > which
        > > > > > > > can have side effects far worse. The amount that a power cord can
        > > > >
        > > > > > > help
        > > > > > > > varies with prevaling conditions. Very simple, single point
        > > > > ground,
        > > > > > > > tube analogue systems are a far better situation to begin with
        > > > > > > than a
        > > > > > > > broadbanded solidstate digital system. Hope this helps. - George
        > > > >
        > > > > > > > __________
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