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Help with op amp voltages

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  • Help with op amp voltages

    I have been working on my Sansamp Classic to get it to work. And gone as far as removing all switches, and most of the input buffer. When this was all together, I had the controls cranked and barely got any noise. If I hit the strings hard I got the noise but sounded shorted, gated sounding. When I turned the volume control I get a crackle sound (crackle not okay). Now with switches removed, and input buffer still the same problems.
    I am still getting almost 1 volt lower on my first stage of IC1 (see below). Does anyone have any voltage readings for this project? Should these pins all be close to the same voltage? What components affect the voltage for that first stage?



    Q1
    Drain 7.93v
    Gate 4.183v
    Source 0v

    IC1
    pin 1 4.381v
    Pin 2 4.58v
    Pin 3 3.67v
    Pin 4 0v
    pin 5 4.34v
    Pin 6 4.38v
    Pin 7 4.41v
    Pin 8 7.93v

    IC2
    Pin 1 4.386v
    Pin 2 4.386v
    Pin 3 4.357v
    Pin 4 7.91v
    Pin 5 4.373v
    Pin 6 4.383v
    Pin 7 4.382v
    Pin 8 4.36v
    Pin 9 4.24v
    Pin 10 4.25v
    Pin 11 0v
    Pin 12 4.354v
    Pin 13 4.383v
    Pin 14 4.359v

  • #2
    MAKE SURE YOU HAVE YOUR JFETS IN THE RIGHT DIRECTION!!! This pedal calls for a 2SK117, and I can not get them. So I used a J201. Printed out the data sheets, and thought they just needed to be reversed. Nope, bend one leg to the side, and the middle out.

    Never give up, I spent the last two nights trying to get this to work. Tonight using a audio probe (again) it just didn't seem right. Sound going into the gate but nothing out of the source. Than I looked at the data sheets (again). And finally saw it.

    Now I need to solder all those switches back in. Think I will have a beer first...

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    • #3
      I did get this back all together, and now it works.

      But I am still curious about the voltage on the first stage of IC1. Pin 3 is still less voltage than pin 2, or pin 1 and the distortion does not seem as much as in the demos I hear. I read in a article on Geofex that the voltages should be within mvolts of each pin. Right now I am reading:

      Pin 1 4.2v
      Pin 2 4.2v
      Pin 3 3.8v

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