Fuzz face - how to bias with multimeter

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    • Fuzz face - how to bias with multimeter

      Hi all,

      Hope everyone is staying safe.
      Can someone please help with how I bias the das musikding silicon fuzz face?

      Do I remove one of the silicon transistors and insert the positive probe into one of those holes, and tab negative to side of the pedal case?

      And do I have it plugged in to both input and output cables and use a 9v battery? And do I put both volume and fuzz knob at 12 o'clock?

      Sorry for stupid questions, I've tried everything and still got no idea. I get no reading whatever I try. My assumption I'm trying to get to 4.5v.

      Here the schematic.
      musikding.de/TThe-Face-Silicon-Fuzz-kit

      Cheers for any help,
      Sean
    • HI Sean,

      With no transistors installed no current can flow so you need both installed. Usually the input jack is wired as such that with no plug in it the ground gets separated to prevent the thing from being on all the time and draining the battery.
      Use a battery, check voltage on the board connection, if nothings there put a plug into the input, check voltage again.
      Most of the times the case is grounded through the jacks or the pots so ground on the battery should be connected to gound on the PCB and the case.
      If you have power on the board: Q1 is getting biased by Q2 via R3. Q2 is biased by direct connection to the Collector of Q1 and R2. To set the bias for Q2 and Q1 you need to fiddle with that little trimpot RV1. Measure positive at the lug or the collector of Q2 against ground or the case.Turn the pot and see what happens. Try to get to 4.5 or a bit higher. I personally ternd to a more positive bias but thats a matter of taste and try. Check Voltage at collector of Q1 or R2, this should also be in the region of 4.5V again something to play with. For setting the bias i would first set the fuzz knob to 0. Then try the sound with different settings and find the one to your liking.
      Maybe shorten the input to ground if you get no stable reading.

      Cheers and stay safe,
      Olaf

      The post was edited 1 time, last by tubes3000 ().