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I've just build the circuit on a breadboard using original schematic (normal channel). No issues, no farting sounds. Not much gain (less than I expected). It's a bit late now to properly test it with a guitar.

Take an audio probe and check stage by stage where it starts to appear. Input -> buffer -> 1st op amp -> 2nd -> EQ -> and so on.. I'd also build another unit but on a breadboard, just to compare them.

So.. it's possible that you have around 1V on a J113 drain, mayble less. With J201 you have around 5-6V. Assuming you changed only transistor, without adjusting Rd (R13 or R12) or Rs. That's because J113 has higher Vp and Idss. This 1V is way too low. You can change source resistance to 3k9 or...

What's the voltage on the J113 drain?

Hope dies last :) Jump Drive... Revised 10/28/22... Schematic coming soon

You can save vectorized graphic as svg or pdf.

You can trace bitmaps in Inkscape. https://www.dafont.com/

I'm afraid oscillations are a built-in feature.. you're not the only one with the same issue.

Thank you both for the tips. I'll try them out soon. SpinCAD. I have no experience with programming so this is the only way for me for now. SpinCAD -> hex -> bin -> AsProgrammer

Thinking about EQ type patch for the FV-1. What I need - bandpass filter with two notch filters. For example: 100Hz to 5kHz with notches at 500Hz and 2kHz. Each notch has fixed frequency, fixed Q and adjustable depth (from zero to -10dB). Is it possible? Any tips?

I suspect that Locrian99 has swapped the pin designations. S - ok.. D - could be this 7.18V G - should be 0

nothing..absolutely nothing. You can even not install Sag pot before setting the bias. Jumper pads 1 and 2 of the Sag pot, set the bias, install the pot. Looking at the schematic of the v1 and v2 there's no difference between Sag pot wiring, unless there is an earlier version of the schematic.

But you know you have to set 6V on a test points, right? And only when Sag does not limit the voltage?

First let's make sure you're doing everything correctly. 1. Set the maximum voltage on the pin 1 of the Sag knob. Sag should be probably at zero (max CCW) but it's better to measure the voltage than stare at the knob. From now on - do not adjust Sag. You want max voltage.. like there's no Sag...

Do not rely on the Sag knob position. Measure voltage in the circuit - you want max possible voltage on pin 1 of the Sag.

Because audio signal can affect the bias voltage.

No, I haven't even started yet. I would prefer to use the full schematic rather than with some modules omitted.

@Robert - any update on this?

Thank you for your offer. I think I already have everything I need to design a pcb. I like this part of the build and I like to lay a board in my own way :) I'll post an update here. Thanks again.

@Paul.Ruby thanks for the schematic and explanations. Now I have to find some time to process it and probably design a board for the O2.