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Re: [softrock40] Re: Failure modes of LT6231?

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  • Ethan Miller K8GU
    Mike---that makes sense. When one channel was still working on the old op amp, the SNR (on only one of the component channels) was fine. So, I don t think it
    Message 1 of 7 , Oct 27, 2011
      Mike---that makes sense. When one channel was still working on the
      old op amp, the SNR (on only one of the component channels) was fine.
      So, I don't think it was an on-going thing. Maybe a transient when I
      plugged in like Mike, AK3F, describes.

      Thanks and 73,

      --Ethan, K8GU/3.

      On Thu, Oct 27, 2011 at 12:16 AM, vbifyz <3ym3ym@...> wrote:
      > Not sure about destroying the LT6231, but any voltage between the power ground and the soundcard ground will destroy the signal-to-noise for sure first. The Softrock power supply has to be floating with respect to the computer ground, with as low stray capacitance as possible between the PS ground and any large objects.
      >
      > A battery is ideal in this respect. A small wall wart is ok. Using USB power for 5V (bypassing the 78L05 regulator) may be ok, because there is usually not much noise between the USB ground and the soundcard ground. A PS with a large 60Hz transformer is bad. A grounded negative power rail is the worst.
      >
      > 73, Mike
      >
      > --- In softrock40@yahoogroups.com, Ethan Miller K8GU <ethan@...> wrote:
      >>
      >> Ok, box from Digi-Key arrived today and I removed the original
      >> (suspect) LT6231 from the board.  Before I installed a new one, I
      >> checked all of the voltages...perfect 2.5 volts all around, except
      >> pins 4 and 8, which were 0 and 5, respectively.  Then, I installed the
      >> new one.
      >>
      >> Powered up with an SLA battery instead of the station power supply.
      >> Works great---I have both channels I and Q now and the image rejection
      >> is working.
      >>
      >> So, the question is:  Has anybody else seen the failure that Tony
      >> suggested---a small stray AC voltage between the audio card ground and
      >> the supply ground destroying the LT6231?  Do I dare reconnect it to my
      >> station power bus?  I bought plenty of LT6231s, but I'm loathe to
      >> start popping them left and right at 4 USD each.
      >>
      >> Thanks and 73,
      >>
      >> --Ethan, K8GU/3.
      >>
      >>
      >
      >
      >
      >
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      --
      http://www.k8gu.com/
      Repair.  Re-use.  Re-purpose.  Recycle.
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