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Re: [softrock40] audio isolation transfomers

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  • dan edwards
    thanks, jack   i have looked at your site. great work. guess i overlooked this, though.   so, quick easy answer is No great advantage with the triad over
    Message 1 of 10 , Jul 2, 2009
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      thanks, jack
       
      i have looked at your site. great work. guess i overlooked this, though.
       
      so, quick easy answer is "No great advantage with the triad over the r.s. cheapie" ??
       
      even with a passing attempt at 'better' impedance matching? i find a variety
      of z ratio triads are available. is my read of the tech specs of the 0202 daughter
      card input z of 10k ohms correct?
       
      73, w5xz, dan


      --- On Thu, 7/2/09, Jack Smith <Jack.Smith@...> wrote:

      From: Jack Smith <Jack.Smith@...>
      Subject: Re: [softrock40] audio isolation transfomers
      To: softrock40@yahoogroups.com
      Date: Thursday, July 2, 2009, 10:12 AM

      Comparisons of the Radio Shack transformer and Triad SP-70 at
      http://www.cliftonl aboratories. com/softrock_ lite_6_2. htm

      Jack K8ZOA

      w5xz@... wrote:
      >
      >
      > i have a nasty ground loop with my emu1212; since it HAS
      > balanced line inputs, i put a couple of cheapie radio
      > shack isolation transformers (p/n 271-1374) in, and
      > re-wired to the balanced inputs, with twisted pairs only.
      > at $3 each, it was too cheap to pass up.
      >
      > now, there is a narrow but distinct notch around 0 Hz.
      > about 20 db or so. beats the heck out of that noise hump, though...
      >
      > i suppose this is low freq roll-off? pleasantly surprised to
      > see plenty of signal many many khz away from 0 hz, though.
      > plus & minus 75 khz, plus.......sampling at 192k with the emu.
      >
      > overall, rx sensitivity seems better, also. with no particular
      > attempt at impedance matching either; 1:1 transformers, supposedly
      > i'm guessing the rxtx6.3 is about 50 ohms out, and i think
      > the emu is 15k ohms in........
      >
      > do the good triad isolation transfomers do this also?
      >
      > 73, w5xz, dan
      >
      >
    • Jack Smith
      Dan: I believe the 10K is correct. The output impedance of the Softrock is near zero. After all, it is an op amp in a feedback circuit so it tries to maintain
      Message 2 of 10 , Jul 2, 2009
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        Dan:

        I believe the 10K is correct.

        The output impedance of the Softrock is near zero. After all, it is an
        op amp in a feedback circuit so it tries to maintain the same output
        voltage regardless of the load on it. Hence its output impedance is in
        theory zero, limited only by the op-amps ability to source or sink
        current plus the impedance of the blocking capacitor.

        So you are not matching the Softrock to the sound card's input impedance
        in any normal sense of the term 'matching.' Rather the transformer
        ratios serve as a voltage step up more than anything else.

        You can think of the sound card as if it's a voltmeter - you don't want
        to match the volt meter's high input impedance to the voltage source you
        are measuring. If you don't need the voltage step up, a 1:1 transformer
        ratio is fine. Could be 600:600 or 10K:10K. I doubt very much that you
        will find any benefit in a ratio other than 1:1 with an E MU 0202.

        Of course there are some practical issues related to stray capacitance
        in the transformer windings and how they alter the transformer's high
        frequency response into various loads. You can see some of this in my
        various transformer pages. Hence, I would stick with the 600:600
        versions and deviate from that only if you know what you are doing.

        Jack

        dan edwards wrote:
        >
        >
        > thanks, jack
        >
        > i have looked at your site. great work. guess i overlooked this, though.
        >
        > so, quick easy answer is "No great advantage with the triad over the
        > r.s. cheapie" ??
        >
        > even with a passing attempt at 'better' impedance matching? i find a
        > variety
        > of z ratio triads are available. is my read of the tech specs of the
        > 0202 daughter
        > card input z of 10k ohms correct?
        >
        > 73, w5xz, dan
        >
        >
        > --- On *Thu, 7/2/09, Jack Smith /<Jack.Smith@...>/* wrote:
        >
        >
        > From: Jack Smith <Jack.Smith@...>
        > Subject: Re: [softrock40] audio isolation transfomers
        > To: softrock40@yahoogroups.com
        > Date: Thursday, July 2, 2009, 10:12 AM
        >
        > Comparisons of the Radio Shack transformer and Triad SP-70 at
        > http://www.cliftonl aboratories. com/softrock_ lite_6_2. htm
        > <http://www.cliftonlaboratories.com/softrock_lite_6_2.htm>
        >
        > Jack K8ZOA
        >
        > w5xz@...
        > <http://us.mc1802.mail.yahoo.com/mc/compose?to=w5xz%40att.net> wrote:
        > >
        > >
        > > i have a nasty ground loop with my emu1212; since it HAS
        > > balanced line inputs, i put a couple of cheapie radio
        > > shack isolation transformers (p/n 271-1374) in, and
        > > re-wired to the balanced inputs, with twisted pairs only.
        > > at $3 each, it was too cheap to pass up.
        > >
        > > now, there is a narrow but distinct notch around 0 Hz.
        > > about 20 db or so. beats the heck out of that noise hump, though...
        > >
        > > i suppose this is low freq roll-off? pleasantly surprised to
        > > see plenty of signal many many khz away from 0 hz, though.
        > > plus & minus 75 khz, plus.......sampling at 192k with the emu.
        > >
        > > overall, rx sensitivity seems better, also. with no particular
        > > attempt at impedance matching either; 1:1 transformers, supposedly
        > > i'm guessing the rxtx6.3 is about 50 ohms out, and i think
        > > the emu is 15k ohms in........
        > >
        > > do the good triad isolation transfomers do this also?
        > >
        > > 73, w5xz, dan
        > >
        > >
        >
        >
      • Jeff Blaine AC0C
        Dan, Jack is the master. Lot of worse ways to waste time than camping out on his page for some review... I had an instance where the ground loop was causing a
        Message 3 of 10 , Jul 2, 2009
        • 0 Attachment
          Dan,
           
          Jack is the master.  Lot of worse ways to waste time than camping out on his page for some review...
           
          I had an instance where the ground loop was causing a gigantic rise near the zero and extending up maybe 10 kHz.  Unbelievable mess.  And rather than actually track down the source of the ground loop (the shack wiring was a mess as well and that would have been a week long project), I stuck in the transformers based on Jack's review of the RS cheap transformer.  Great results - very similar to what you have seen.  A much improved noise profile - but quite deep nulls near the zero point.
           
          So I played around with the coupling cap value, and put a resistor on the sound-card side in an attempt to fill in the center a bit.  Some improvement was had - but it's not picture perfect.  The nulls are about 10db, and pretty narrow.  It looks a bit funky on the screen, but in a practical sense, it's rare that the signal of interest is right in the null - I run a 7-15khz offset depending on sound card frequency - I try to use the highest offset possible, just to minimize the effect of the zero frequency which can be minimized, but never eliminated.
           
          I want to say the cap value went from 0.1->0.2 which helped fill in null a but but gave rise to a larger "bump" near the CF.  The loading resistor was about 6K and that seemed to be about the best overall compromise value.
           
          Putting in the tx was a huge improvement.  And the cap/resistor were probably mostly window dressing, in the overall scheme.
           
          Good luck and hope this helps a bit.
           
          73/jeff/ac0c
           

           
          Sent: Thursday, July 02, 2009 8:28 PM
          Subject: Re: [softrock40] audio isolation transfomers

          Dan:

          I believe the 10K is correct.

          The output impedance of the Softrock is near zero. After all, it is an
          op amp in a feedback circuit so it tries to maintain the same output
          voltage regardless of the load on it. Hence its output impedance is in
          theory zero, limited only by the op-amps ability to source or sink
          current plus the impedance of the blocking capacitor.

          So you are not matching the Softrock to the sound card's input impedance
          in any normal sense of the term 'matching.' Rather the transformer
          ratios serve as a voltage step up more than anything else.

          You can think of the sound card as if it's a voltmeter - you don't want
          to match the volt meter's high input impedance to the voltage source you
          are measuring. If you don't need the voltage step up, a 1:1 transformer
          ratio is fine. Could be 600:600 or 10K:10K. I doubt very much that you
          will find any benefit in a ratio other than 1:1 with an E MU 0202.

          Of course there are some practical issues related to stray capacitance
          in the transformer windings and how they alter the transformer' s high
          frequency response into various loads. You can see some of this in my
          various transformer pages. Hence, I would stick with the 600:600
          versions and deviate from that only if you know what you are doing.

          Jack

          dan edwards wrote:

          >
          >
          > thanks, jack
          >
          > i have looked at
          your site. great work. guess i overlooked this, though.
          >
          > so,
          quick easy answer is "No great advantage with the triad over the
          > r.s.
          cheapie" ??
          >
          > even with a passing attempt at 'better' impedance
          matching? i find a
          > variety
          > of z ratio triads are available. is
          my read of the tech specs of the
          > 0202 daughter
          > card input z of
          10k ohms correct?
          >
          > 73, w5xz, dan
          >
          >
          > --- On
          *Thu, 7/2/09, Jack Smith /<Jack.Smith@cox. net>/* wrote:
          >
          >
          > From: Jack Smith <
          href="mailto:Jack.Smith%40cox.net">Jack.Smith@cox. net>
          >
          Subject: Re: [softrock40] audio isolation transfomers
          > To:
          href="mailto:softrock40%40yahoogroups.com">softrock40@yahoogro ups.com
          >
          Date: Thursday, July 2, 2009, 10:12 AM
          >
          > Comparisons of the Radio
          Shack transformer and Triad SP-70 at
          >
          href="http://www.cliftonl">http://www.cliftonl aboratories. com/softrock_ lite_6_2. htm
          > <
          href="http://www.cliftonlaboratories.com/softrock_lite_6_2.htm">http://www.cliftonl aboratories. com/softrock_ lite_6_2. htm>
          >
          >
          Jack K8ZOA
          >
          >
          href="mailto:w5xz%40att.net">w5xz@...
          > <
          href="http://us.mc1802.mail.yahoo.com/mc/compose?to=w5xz%40att.net">http://us.mc1802. mail.yahoo. com/mc/compose? to=w5xz%40att. net> wrote:
          > >
          > >
          > > i have a nasty ground loop with my
          emu1212; since it HAS
          > > balanced line inputs, i put a couple of
          cheapie radio
          > > shack isolation transformers (p/n 271-1374) in,
          and
          > > re-wired to the balanced inputs, with twisted pairs
          only.
          > > at $3 each, it was too cheap to pass up.
          > >
          > > now, there is a narrow but distinct notch around 0 Hz.
          > > about
          20 db or so. beats the heck out of that noise hump, though...
          > >
          > > i suppose this is low freq roll-off? pleasantly surprised
          to
          > > see plenty of signal many many khz away from 0 hz,
          though.
          > > plus & minus 75 khz, plus.......sampling at 192k with
          the emu.
          > >
          > > overall, rx sensitivity seems better, also.
          with no particular
          > > attempt at impedance matching either; 1:1
          transformers, supposedly
          > > i'm guessing the rxtx6.3 is about 50 ohms
          out, and i think
          > > the emu is 15k ohms in........
          > >
          > > do the good triad isolation transfomers do this also?
          > >
          > > 73, w5xz, dan
          > >
          > >
          >
          >

        • dan edwards
          jack & jeff   thanks for the feedback.   jack, my rxtx6.3 has 100 ohms in series with the outputs of the op amps, along with .1 ufd.  so, that means the
          Message 4 of 10 , Jul 2, 2009
          • 0 Attachment
            jack & jeff
             
            thanks for the feedback.
             
            jack, my rxtx6.3 has 100 ohms in series with the outputs of the op amps, along
            with .1 ufd.  so, that means the output impedance is 100 ohms or so, right?
            a higher impedance ratio, in to out, would just give me a small voltage gain, as
            long as i dont create some funky resonances, right? but not really a significant
            advantage to try to match 100 to 10000 ohms?
             
            jeff: yes, i thought about switching the blocking cap to a much larger value, say
            1 or 10 ufd. this is a good place for a tantalum cap, instead of a b-flat electrolytic?
            the 3 dollar radio shack unit is right in line with the budget for this project!!! ha.
            dirt cheap and actually works pretty well.
             
            73, w5xz, dan

            --- On Thu, 7/2/09, Jeff Blaine AC0C <keepwalking188@...> wrote:

            From: Jeff Blaine AC0C <keepwalking188@...>
            Subject: Re: [softrock40] audio isolation transfomers
            To: softrock40@yahoogroups.com
            Date: Thursday, July 2, 2009, 1:09 PM

            Dan,
             
            Jack is the master.  Lot of worse ways to waste time than camping out on his page for some review...
             
            I had an instance where the ground loop was causing a gigantic rise near the zero and extending up maybe 10 kHz.  Unbelievable mess.  And rather than actually track down the source of the ground loop (the shack wiring was a mess as well and that would have been a week long project), I stuck in the transformers based on Jack's review of the RS cheap transformer.  Great results - very similar to what you have seen.  A much improved noise profile - but quite deep nulls near the zero point.
             
            So I played around with the coupling cap value, and put a resistor on the sound-card side in an attempt to fill in the center a bit.  Some improvement was had - but it's not picture perfect.  The nulls are about 10db, and pretty narrow.  It looks a bit funky on the screen, but in a practical sense, it's rare that the signal of interest is right in the null - I run a 7-15khz offset depending on sound card frequency - I try to use the highest offset possible, just to minimize the effect of the zero frequency which can be minimized, but never eliminated.
             
            I want to say the cap value went from 0.1->0.2 which helped fill in null a but but gave rise to a larger "bump" near the CF.  The loading resistor was about 6K and that seemed to be about the best overall compromise value.
             
            Putting in the tx was a huge improvement.  And the cap/resistor were probably mostly window dressing, in the overall scheme.
             
            Good luck and hope this helps a bit.
             
            73/jeff/ac0c
             

             
            Sent: Thursday, July 02, 2009 8:28 PM
            Subject: Re: [softrock40] audio isolation transfomers

            Dan:

            I believe the 10K is correct.

            The output impedance of the Softrock is near zero. After all, it is an
            op amp in a feedback circuit so it tries to maintain the same output
            voltage regardless of the load on it. Hence its output impedance is in
            theory zero, limited only by the op-amps ability to source or sink
            current plus the impedance of the blocking capacitor.

            So you are not matching the Softrock to the sound card's input impedance
            in any normal sense of the term 'matching.' Rather the transformer
            ratios serve as a voltage step up more than anything else.

            You can think of the sound card as if it's a voltmeter - you don't want
            to match the volt meter's high input impedance to the voltage source you
            are measuring. If you don't need the voltage step up, a 1:1 transformer
            ratio is fine. Could be 600:600 or 10K:10K. I doubt very much that you
            will find any benefit in a ratio other than 1:1 with an E MU 0202.

            Of course there are some practical issues related to stray capacitance
            in the transformer windings and how they alter the transformer' s high
            frequency response into various loads. You can see some of this in my
            various transformer pages. Hence, I would stick with the 600:600
            versions and deviate from that only if you know what you are doing.

            Jack

            dan edwards wrote:
            >
            >
            > thanks, jack
            >
            > i have looked at your site. great work. guess i overlooked this, though.
            >
            > so, quick easy answer is "No great advantage with the triad over the
            > r.s. cheapie" ??
            >
            > even with a passing attempt at 'better' impedance matching? i find a
            > variety
            > of z ratio triads are available. is my read of the tech specs of the
            > 0202 daughter
            > card input z of 10k ohms correct?
            >
            > 73, w5xz, dan
            >
            >
            > --- On *Thu, 7/2/09, Jack Smith /<Jack.Smith@cox. net>/* wrote:
            >
            >
            > From: Jack Smith <Jack.Smith@cox. net>
            > Subject: Re: [softrock40] audio isolation transfomers
            > To: softrock40@yahoogro ups.com
            > Date: Thursday, July 2, 2009, 10:12 AM
            >
            > Comparisons of the Radio Shack transformer and Triad SP-70 at
            > http://www.cliftonl aboratories. com/softrock_ lite_6_2. htm
            > <http://www.cliftonl aboratories. com/softrock_ lite_6_2. htm>
            >
            > Jack K8ZOA
            >
            > w5xz@...
            > <http://us.mc1802. mail.yahoo. com/mc/compose? to=w5xz%40att. net> wrote:
            > >
            > >
            > > i have a nasty ground loop with my emu1212; since it HAS
            > > balanced line inputs, i put a couple of cheapie radio
            > > shack isolation transformers (p/n 271-1374) in, and
            > > re-wired to the balanced inputs, with twisted pairs only.
            > > at $3 each, it was too cheap to pass up.
            > >
            > > now, there is a narrow but distinct notch around 0 Hz.
            > > about 20 db or so. beats the heck out of that noise hump, though...
            > >
            > > i suppose this is low freq roll-off? pleasantly surprised to
            > > see plenty of signal many many khz away from 0 hz, though.
            > > plus & minus 75 khz, plus.......sampling at 192k with the emu.
            > >
            > > overall, rx sensitivity seems better, also. with no particular
            > > attempt at impedance matching either; 1:1 transformers, supposedly
            > > i'm guessing the rxtx6.3 is about 50 ohms out, and i think
            > > the emu is 15k ohms in........
            > >
            > > do the good triad isolation transfomers do this also?
            > >
            > > 73, w5xz, dan
            > >
            > >
            >
            >
          • Matt Palmer
            I d avoid tantalums, green polystyrenes are better for this. Matt W8ESE Former KD8DAO http://blog.MattIsKichigai.com
            Message 5 of 10 , Jul 2, 2009
            • 0 Attachment
              I'd avoid tantalums, green polystyrenes are better for this.


              Matt
              W8ESE
              Former KD8DAO
              http://blog.MattIsKichigai.com



              On Thu, Jul 2, 2009 at 9:12 AM, dan edwards<w5xz@...> wrote:
              >
              >
              > jack & jeff
              >
              > thanks for the feedback.
              >
              > jack, my rxtx6.3 has 100 ohms in series with the outputs of the op amps,
              > along
              > with .1 ufd.  so, that means the output impedance is 100 ohms or so, right?
              > a higher impedance ratio, in to out, would just give me a small voltage
              > gain, as
              > long as i dont create some funky resonances, right? but not really a
              > significant
              > advantage to try to match 100 to 10000 ohms?
              >
              > jeff: yes, i thought about switching the blocking cap to a much larger
              > value, say
              > 1 or 10 ufd. this is a good place for a tantalum cap, instead of a b-flat
              > electrolytic?
              > the 3 dollar radio shack unit is right in line with the budget for this
              > project!!! ha.
              > dirt cheap and actually works pretty well.
              >
              > 73, w5xz, dan
              > --- On Thu, 7/2/09, Jeff Blaine AC0C <keepwalking188@...> wrote:
              >
              > From: Jeff Blaine AC0C <keepwalking188@...>
              > Subject: Re: [softrock40] audio isolation transfomers
              > To: softrock40@yahoogroups.com
              > Date: Thursday, July 2, 2009, 1:09 PM
              >
              > Dan,
              >
              > Jack is the master.  Lot of worse ways to waste time than camping out on his
              > page for some review...
              >
              > I had an instance where the ground loop was causing a gigantic rise near the
              > zero and extending up maybe 10 kHz.  Unbelievable mess.  And rather than
              > actually track down the source of the ground loop (the shack wiring was a
              > mess as well and that would have been a week long project), I stuck in the
              > transformers based on Jack's review of the RS cheap transformer.  Great
              > results - very similar to what you have seen.  A much improved noise profile
              > - but quite deep nulls near the zero point.
              >
              > So I played around with the coupling cap value, and put a resistor on the
              > sound-card side in an attempt to fill in the center a bit.  Some improvement
              > was had - but it's not picture perfect.  The nulls are about 10db, and
              > pretty narrow.  It looks a bit funky on the screen, but in a practical
              > sense, it's rare that the signal of interest is right in the null - I run a
              > 7-15khz offset depending on sound card frequency - I try to use the highest
              > offset possible, just to minimize the effect of the zero frequency which can
              > be minimized, but never eliminated.
              >
              > I want to say the cap value went from 0.1->0.2 which helped fill in null a
              > but but gave rise to a larger "bump" near the CF.  The loading resistor was
              > about 6K and that seemed to be about the best overall compromise value.
              >
              > Putting in the tx was a huge improvement.  And the cap/resistor were
              > probably mostly window dressing, in the overall scheme.
              >
              > Good luck and hope this helps a bit.
              >
              > 73/jeff/ac0c
              >
              >
              > From: Jack Smith
              > Sent: Thursday, July 02, 2009 8:28 PM
              > To: softrock40@yahoogro ups.com
              > Subject: Re: [softrock40] audio isolation transfomers
              > Dan:
              >
              > I believe the 10K is correct.
              >
              > The output impedance of the Softrock is near zero. After all, it is an
              > op amp in a feedback circuit so it tries to maintain the same output
              > voltage regardless of the load on it. Hence its output impedance is in
              > theory zero, limited only by the op-amps ability to source or sink
              > current plus the impedance of the blocking capacitor.
              >
              > So you are not matching the Softrock to the sound card's input impedance
              > in any normal sense of the term 'matching.' Rather the transformer
              > ratios serve as a voltage step up more than anything else.
              >
              > You can think of the sound card as if it's a voltmeter - you don't want
              > to match the volt meter's high input impedance to the voltage source you
              > are measuring. If you don't need the voltage step up, a 1:1 transformer
              > ratio is fine. Could be 600:600 or 10K:10K. I doubt very much that you
              > will find any benefit in a ratio other than 1:1 with an E MU 0202.
              >
              > Of course there are some practical issues related to stray capacitance
              > in the transformer windings and how they alter the transformer' s high
              > frequency response into various loads. You can see some of this in my
              > various transformer pages. Hence, I would stick with the 600:600
              > versions and deviate from that only if you know what you are doing.
              >
              > Jack
              >
              > dan edwards wrote:
              >>
              >>
              >> thanks, jack
              >>
              >> i have looked at your site. great work. guess i overlooked this, though.
              >>
              >> so, quick easy answer is "No great advantage with the triad over the
              >> r.s. cheapie" ??
              >>
              >> even with a passing attempt at 'better' impedance matching? i find a
              >> variety
              >> of z ratio triads are available. is my read of the tech specs of the
              >> 0202 daughter
              >> card input z of 10k ohms correct?
              >>
              >> 73, w5xz, dan
              >>
              >>
              >> --- On *Thu, 7/2/09, Jack Smith /<Jack.Smith@cox. net>/* wrote:
              >>
              >>
              >> From: Jack Smith <Jack.Smith@cox. net>
              >> Subject: Re: [softrock40] audio isolation transfomers
              >> To: softrock40@yahoogro ups.com
              >> Date: Thursday, July 2, 2009, 10:12 AM
              >>
              >> Comparisons of the Radio Shack transformer and Triad SP-70 at
              >> http://www.cliftonl aboratories. com/softrock_ lite_6_2. htm
              >> <http://www.cliftonl aboratories. com/softrock_ lite_6_2. htm>
              >>
              >> Jack K8ZOA
              >>
              >> w5xz@...
              >> <http://us.mc1802 mail.yahoo. com/mc/compose? to=w5xz%40att. net> wrote:
              >> >
              >> >
              >> > i have a nasty ground loop with my emu1212; since it HAS
              >> > balanced line inputs, i put a couple of cheapie radio
              >> > shack isolation transformers (p/n 271-1374) in, and
              >> > re-wired to the balanced inputs, with twisted pairs only.
              >> > at $3 each, it was too cheap to pass up.
              >> >
              >> > now, there is a narrow but distinct notch around 0 Hz.
              >> > about 20 db or so. beats the heck out of that noise hump, though...
              >> >
              >> > i suppose this is low freq roll-off? pleasantly surprised to
              >> > see plenty of signal many many khz away from 0 hz, though.
              >> > plus & minus 75 khz, plus.......sampling at 192k with the emu.
              >> >
              >> > overall, rx sensitivity seems better, also. with no particular
              >> > attempt at impedance matching either; 1:1 transformers, supposedly
              >> > i'm guessing the rxtx6.3 is about 50 ohms out, and i think
              >> > the emu is 15k ohms in........
              >> >
              >> > do the good triad isolation transfomers do this also?
              >> >
              >> > 73, w5xz, dan
              >> >
              >> >
              >>
              >>
              >
              >
            • Alan
              With regard to transformer ratio, if it steps up the voltage to the soundcard then would the Softrock gain need to be reduced? Softrocks are normally sensitive
              Message 6 of 10 , Jul 2, 2009
              • 0 Attachment
                With regard to transformer ratio, if it steps up the voltage to the
                soundcard then would the Softrock gain need to be reduced?
                Softrocks are normally sensitive enough so extra voltage could reduce the
                dynamic range.

                From: "Jeff Blaine AC0C"

                >I had an instance where the ground loop was causing a gigantic rise near
                >the zero and extending up maybe 10 kHz. Unbelievable mess. And >rather
                >than actually track down the source of the ground loop (the shack wiring
                >was a mess as well

                Some might enjoy the challenge! However it may not be easy if it is all
                boxed up before you start. It is most likely the proplems lie between what
                is connected between ground, the computer and to the Softrock. That's the
                path you have broken.


                73 Alan G4ZFQ
              • Jack Smith
                Dan: If you add a 100 to 10000 ohm matching transformer, the result is a 10:1 step up in voltage. The E MU 0202 10K input resistance will then reflect back to
                Message 7 of 10 , Jul 2, 2009
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                  Dan:

                  If you add a 100 to 10000 ohm matching transformer, the result is a 10:1
                  step up in voltage.

                  The E MU 0202 10K input resistance will then reflect back to the
                  transformer primary as 100 ohms, so you will see a 6 dB loss due to
                  voltage dividing based on the 100 ohm series R in your Softrock. This
                  nets out at 5:1 voltage step up, measuring from the op-amp output to the
                  E MU 0202 input.

                  My experience is that the E MU 0202 does not need extra voltage gain
                  with the Softrock Lite, and the net effect of 'matching' the impedances
                  will be to cause you to have to turn the E MU 0202's gain down to avoid
                  overloading on peaks.

                  You get to the same place by using a 1:1 transformer. In this case 10K
                  on the secondary reflects back as 10K on the primary, which causes
                  negligible drop across the 100 ohm series resistance and for most
                  practical purposes the full voltage output of the op-amp is delivered to
                  the E MU 0202's input.

                  My belief is that you don't need a 100 ohm to 10K transformer for the
                  reasons stated above.

                  Jack K8ZOA


                  dan edwards wrote:
                  >
                  >
                  > jack & jeff
                  >
                  > thanks for the feedback.
                  >
                  > jack, my rxtx6.3 has 100 ohms in series with the outputs of the op
                  > amps, along
                  > with .1 ufd. so, that means the output impedance is 100 ohms or so,
                  > right?
                  > a higher impedance ratio, in to out, would just give me a small
                  > voltage gain, as
                  > long as i dont create some funky resonances, right? but not really a
                  > significant
                  > advantage to try to match 100 to 10000 ohms?
                  >
                  > jeff: yes, i thought about switching the blocking cap to a much larger
                  > value, say
                  > 1 or 10 ufd. this is a good place for a tantalum cap, instead of a
                  > b-flat electrolytic?
                  > the 3 dollar radio shack unit is right in line with the budget for
                  > this project!!! ha.
                  > dirt cheap and actually works pretty well.
                  >
                  > 73, w5xz, dan
                  >
                  > --- On *Thu, 7/2/09, Jeff Blaine AC0C /<keepwalking188@...>/* wrote:
                  >
                  >
                  > From: Jeff Blaine AC0C <keepwalking188@...>
                  > Subject: Re: [softrock40] audio isolation transfomers
                  > To: softrock40@yahoogroups.com
                  > Date: Thursday, July 2, 2009, 1:09 PM
                  >
                  > Dan,
                  >
                  > Jack is the master. Lot of worse ways to waste time than camping
                  > out on his page for some review...
                  >
                  > I had an instance where the ground loop was causing a gigantic
                  > rise near the zero and extending up maybe 10 kHz. Unbelievable
                  > mess. And rather than actually track down the source of the
                  > ground loop (the shack wiring was a mess as well and that would
                  > have been a week long project), I stuck in the transformers based
                  > on Jack's review of the RS cheap transformer. Great results
                  > - very similar to what you have seen. A much improved noise
                  > profile - but quite deep nulls near the zero point.
                  >
                  > So I played around with the coupling cap value, and put a resistor
                  > on the sound-card side in an attempt to fill in the center a bit.
                  > Some improvement was had - but it's not picture perfect. The
                  > nulls are about 10db, and pretty narrow. It looks a bit funky on
                  > the screen, but in a practical sense, it's rare that the signal of
                  > interest is right in the null - I run a 7-15khz offset depending
                  > on sound card frequency - I try to use the highest offset
                  > possible, just to minimize the effect of the zero frequency which
                  > can be minimized, but never eliminated.
                  >
                  > I want to say the cap value went from 0.1->0.2 which helped fill
                  > in null a but but gave rise to a larger "bump" near the CF. The
                  > loading resistor was about 6K and that seemed to be about the best
                  > overall compromise value.
                  >
                  > Putting in the tx was a huge improvement. And the cap/resistor
                  > were probably mostly window dressing, in the overall scheme.
                  >
                  > Good luck and hope this helps a bit.
                  >
                  > 73/jeff/ac0c
                  >
                  >
                  >
                  > *From:* Jack Smith
                  > <http://us.mc1802.mail.yahoo.com/mc/compose?to=Jack.Smith@...>
                  > *Sent:* Thursday, July 02, 2009 8:28 PM
                  > *To:* softrock40@yahoogro ups.com
                  > <http://us.mc1802.mail.yahoo.com/mc/compose?to=softrock40@yahoogroups.com>
                  >
                  > *Subject:* Re: [softrock40] audio isolation transfomers
                  >
                  > Dan:
                  >
                  > I believe the 10K is correct.
                  >
                  > The output impedance of the Softrock is near zero. After all, it
                  > is an
                  > op amp in a feedback circuit so it tries to maintain the same output
                  > voltage regardless of the load on it. Hence its output impedance
                  > is in
                  > theory zero, limited only by the op-amps ability to source or sink
                  > current plus the impedance of the blocking capacitor.
                  >
                  > So you are not matching the Softrock to the sound card's input
                  > impedance
                  > in any normal sense of the term 'matching.' Rather the transformer
                  > ratios serve as a voltage step up more than anything else.
                  >
                  > You can think of the sound card as if it's a voltmeter - you don't
                  > want
                  > to match the volt meter's high input impedance to the voltage
                  > source you
                  > are measuring. If you don't need the voltage step up, a 1:1
                  > transformer
                  > ratio is fine. Could be 600:600 or 10K:10K. I doubt very much that
                  > you
                  > will find any benefit in a ratio other than 1:1 with an E MU 0202.
                  >
                  > Of course there are some practical issues related to stray
                  > capacitance
                  > in the transformer windings and how they alter the transformer' s
                  > high
                  > frequency response into various loads. You can see some of this in my
                  > various transformer pages. Hence, I would stick with the 600:600
                  > versions and deviate from that only if you know what you are doing.
                  >
                  > Jack
                  >
                  > dan edwards wrote:
                  > >
                  > >
                  > > thanks, jack
                  > >
                  > > i have looked at your site. great work. guess i overlooked this,
                  > though.
                  > >
                  > > so, quick easy answer is "No great advantage with the triad over
                  > the
                  > > r.s. cheapie" ??
                  > >
                  > > even with a passing attempt at 'better' impedance matching? i
                  > find a
                  > > variety
                  > > of z ratio triads are available. is my read of the tech specs of
                  > the
                  > > 0202 daughter
                  > > card input z of 10k ohms correct?
                  > >
                  > > 73, w5xz, dan
                  > >
                  > >
                  > > --- On *Thu, 7/2/09, Jack Smith /<Jack.Smith@cox. net
                  > <http://us.mc1802.mail.yahoo.com/mc/compose?to=Jack.Smith%40cox.net>>/*
                  > wrote:
                  > >
                  > >
                  > > From: Jack Smith <Jack.Smith@cox. net
                  > <http://us.mc1802.mail.yahoo.com/mc/compose?to=Jack.Smith%40cox.net>>
                  > > Subject: Re: [softrock40] audio isolation transfomers
                  > > To: softrock40@yahoogro ups.com
                  > <http://us.mc1802.mail.yahoo.com/mc/compose?to=softrock40%40yahoogroups.com>
                  > > Date: Thursday, July 2, 2009, 10:12 AM
                  > >
                  > > Comparisons of the Radio Shack transformer and Triad SP-70 at
                  > > http://www.cliftonl <http://www.cliftonl/> aboratories.
                  > com/softrock_ lite_6_2. htm
                  > > <http://www.cliftonl aboratories. com/softrock_ lite_6_2. htm
                  > <http://www.cliftonlaboratories.com/softrock_lite_6_2.htm>>
                  > >
                  > > Jack K8ZOA
                  > >
                  > > w5xz@...
                  > <http://us.mc1802.mail.yahoo.com/mc/compose?to=w5xz%40att.net>
                  > > <http://us.mc1802 mail.yahoo. com/mc/compose? to=w5xz%40att.
                  > net
                  > <http://us.mc1802.mail.yahoo.com/mc/compose?to=w5xz%40att.net>> wrote:
                  > > >
                  > > >
                  > > > i have a nasty ground loop with my emu1212; since it HAS
                  > > > balanced line inputs, i put a couple of cheapie radio
                  > > > shack isolation transformers (p/n 271-1374) in, and
                  > > > re-wired to the balanced inputs, with twisted pairs only.
                  > > > at $3 each, it was too cheap to pass up.
                  > > >
                  > > > now, there is a narrow but distinct notch around 0 Hz.
                  > > > about 20 db or so. beats the heck out of that noise hump,
                  > though...
                  > > >
                  > > > i suppose this is low freq roll-off? pleasantly surprised to
                  > > > see plenty of signal many many khz away from 0 hz, though.
                  > > > plus & minus 75 khz, plus.......sampling at 192k with the emu.
                  > > >
                  > > > overall, rx sensitivity seems better, also. with no particular
                  > > > attempt at impedance matching either; 1:1 transformers, supposedly
                  > > > i'm guessing the rxtx6.3 is about 50 ohms out, and i think
                  > > > the emu is 15k ohms in........
                  > > >
                  > > > do the good triad isolation transfomers do this also?
                  > > >
                  > > > 73, w5xz, dan
                  > > >
                  > > >
                  > >
                  > >
                  >
                  >
                • Andy
                  ... This may be a really stupid and ignorant question on my part, but as long as the emu 1212 has balanced inputs, can t you use it with its balanced inputs
                  Message 8 of 10 , Jul 2, 2009
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                    > i have a nasty ground loop with my emu1212; since it HAS
                    > balanced line inputs, i put a couple of cheapie radio
                    > shack isolation transformers (p/n 271-1374) in, and
                    > re-wired to the balanced inputs, with twisted pairs only.
                    > at $3 each, it was too cheap to pass up.

                    This may be a really stupid and ignorant question on my part, but as long as
                    the emu 1212 has balanced inputs, can't you use it with its balanced inputs
                    without the transformers? If they are good electronically balanced inputs
                    they mimic what a transformer does and break ground loops.

                    Usually you can go from unbalanced to balanced OK; it's the other direction
                    that may not work.

                    Andy
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