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Cheap signal tracer

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  • Cheap signal tracer

    In cleaning my shop, I find boxes of bits I have saved. One thing I like to do is find an old receiver or tape deck or VCR and strip it down as far as it will go, to the last screw. I find this refreshing when I need to get my head out of what I am doing. I built up a great collection of metric screws that way. I always saved the power transformers, so I have a bunch of small ones from like cassette decks, and larger ones from stereo receivers.

    One thing I find in some better gear are small boards with a headphone amp on it. Some are just a chip and a jack, some have a volume control too. Hookup is intuitve, usually left and right signals, power and ground. Some run the little IC dual supplies, others single supply. Whatever. I think the one I am looking at came from a multidisk CD player.

    I came upon one such board last night, and connected my bench supply to it and put on my phones. It worked. It occurs to me I could use these things as basic signal tracers. Not a lot of gain, but I could easily add a gain stage. I powered it from a 12v supply, but a wall wart would do as well, or even a battery, and those choices leave it unconnected to earth.
    Education is what you're left with after you have forgotten what you have learned.

  • #2
    Very cool! Do you use a cap at the end of a cable as a probe?

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    • #3
      There wasn't one during my test, but I would indeed install one.

      It is just an idea, it may or may not need a gain boost. Or for that matter, the op amp gain is set by resistors, I could tweak those.

      I think I saw a small phones amp board in some Yamaha keyboard too. I had a number more of them saved somewhere, though I may have tossed them.
      Education is what you're left with after you have forgotten what you have learned.

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      • #4
        Ya a small headphone amp would be cool. I have a small battery powered guitar amp that I use with a probe. It has a headphone out but I've never tried it.

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        • #5
          Oh, well nothing wrong with a speaker. I just always have a set of phones hanging next to me, and this little circuit was sitting there in front of me, and...
          Education is what you're left with after you have forgotten what you have learned.

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