Christmas Debug!!!

[mcasey1]

Professor Tweed (from runoffgroove.com) PCB layout.
Passes signal, but the tone control doesnt appear to change tone, there is very low distortion from pedal, and background bacon frying noise.
All Transistors are MPF102s

Q1
D=4.77
G=.47
S=0

Q2
D=4.49
G=1.73
S=0

Q3
D=4.56
G=0.88
S=0

I can post a more thorough voltage listing if necessary.  I think there amy be a prolem around Q1.  Its source seems fairly low.

[petemoore]

Q1
D=4.77
G=.47
S=0

Q2
D=4.49
G=1.73
S=0

Q3
D=4.56
G=0.88
S=0
  I guess pinout, all the sources should be above the gates.
  Transistor print faces input of board, drain on top, source in the middle, gate on the bottom. That's what MPF102's and J201's look like on my boards, I put the source in the middle.
  {many schematics show D/G/S order from top to bottom.
  It is possible to bend the G/S leads 'bently/gently' out </> [front to back],
and around ^_each other to match D/G/S board to D/S/G transistors...and still have them not touch/plug in a socket.
  Verify pinout on board, compare that to the data sheet pinout of the Jfet transistor part # you are installing..Jfet pinouts vary.

[mcasey1]

Oh I just listed the voltages wrong.  The transistors are DSG.  not DGS.

[B Tremblay]

The Q1 and Q2 stages are basically identical, so the voltages should be pretty close.  Swap those two FETs with each other and observe whether they have the same source voltage when you re-bias.

While the Q1 and Q3 source voltages look a little low, they're not so far off that the sound should be affected in the manner that you've described.  FETs can vary a lot, so it's possible that you happened to get some low Vp MPF102.

Look for an offboard wiring error and then check for solder bridges or missing connections.

[mcasey1]

Ive used solid core wires to connect the pots to the board.  While all wires lead to proper lugs and pads, I suspect there may be a short in one of these wires.  Maybe this is why the tone control is ineffective.