Harmonic Jerkulator Layout FIASCO!!! Shape of layout affecting outcome?!?!?

[breather-resistor]

Ok, some time ago I built the harmonic jerkulator.  Its pretty cool, and I want to put it into a smaller box.  I designed my own layout previously and had no issues whatsoever.  Since then I have mad some changes on my pedal board and I want to put it into a smaller box.  So I redesigned the layout to work better with the smaller box and new hardware layout.  Sounds great EXCEPT when I turn down the gain I hear a weird bias/ghosting issue. 

First thoughts in my mind:

Verify Transistor pinouts. Check electrolytic orientation. Check off-board wiring.  Make sure layout is really right to begin with. 

I know it is common for people to post here and say that they have checked these things when really their idea of checking is more like glancing.  To be certain that I was not fooling myself, I built two units (both sharing the problem) 10 times verified the layout and compared the voltage and R to ground at every point of the circuit to the one I previously built.  I am using the same components part for part, which I have had no problems with.  Same transistors from the same batch everything............

My question is this:  I can't determine any difference between these two circuits AT ALL...  I'm not naive enough to believe that the circuits are the same though...  Is it possible that the shape of the layout (IE maybe certain traces running parallel) is causing this issue. 

It sounds like if you took a poorly biased circuit and used a blender to mix it with a correct circuit and it seems to be very connected to the Gain Knob.  Yes, the wiring of the gain knob has been checked (to the max)

Geoff

[Ice-9]

Hi, it could be the way the layout traces run. A couple of picture of the schematic and pcb layout would help a lot.

[breather-resistor]

I've tried inverting G1-G2 and L1-L2

D-led negative
D+led positive

[breather-resistor]

Also there are two dummy resistors there... The ones with no values off of the switch, consider them 0 ohm jumpers.

Thanks,

Geoff

[earthtonesaudio]

That's a lot of close parallel traces.  Might be some capacitive coupling going on.

[breather-resistor]

 

Success!!!  I built another on the old layout and I've never been so excited to hear ghosting and bias grossness in my whole life because it meant that there HAD to  be a component failure.  22k resistors wrecked 4 nights of my life.  They were metering at 22k and still are.  I will be placing a 22k resistive load between multiple pieces of trash in the can.

I've had goofy batches of transistors, diodes, caps, but never resistors.

Thanks for the people that no doubt spent considerable time comparing the layout to the schematic they take longer to diagnose when they are right (ironically).

Oh well, I'm off to the bar to celebrate.

Geoff

[earthtonesaudio]

Congrats!  A successful debugging session is very rewarding.