GuitarPCB Guitar/Bass Driver V2 – Low Output

[LittleRummyTumTum]

I'm having a bit of an unusual issue with a Guitar/Bass Driver V2 build from GuitarPCB. Schem/Layout is here: https://guitarpcb.com/wp-content/uploads/2018/06/BD_GuitarBassDriver-Board.pdf

Basically the effect works, but is very low volume with every knob dimed. I've worked my way through the board with an Audio Probe, and this is where it gets confusing: I get ample volume/signal coming off Q9, but probing the input of c16 the volume has dropped.

Any thoughts here? Looking at the PCB the traces don't appear damaged nor can I see any shorts between Q9 and c16. I did considering swapping out both components, but the signal loss is clearly happening somewhere in between. I'm tempted to just connect Q9s drain, C16, and R27 off the board to bypass it see if that corrects it.

Also note that Q9 was subbed with a J112 - though as the signal coming off the drain with the probe is fine I don't think this is the issue.

EDIT: Scratch that I'm an idiot - I'm actually getting signal coming out of the GATE of each transistor, not the drain for some reason. So if I probe Q1 I get signal on the Gate and Source (probing the leg itself) but nothing on the drain, same applies to Q9

 

[szukalski]

Hard to tell from the pics, maybe it needs a reflow of solder?

 

[HamishR]

Is the pinout of Q9 the same as what you used it for? I believe that some Jfets can work if inserted 180 degrees from intended, so maybe it works but not very well?

 

[music6000]

Pictures are worth a thousand words!
Check that your resistor values are correct in highlighted Boxes.
You can also use a 2N5458 or 57 if you have one for Q9 to see if that is a better option?
With power disconnected, test for continuity at junction pad of Q9 D, R27 & C16 to Ground, if it beeps you have a problem:

 

[LittleRummyTumTum]

Scratch that I'm an idiot - I'm actually getting signal coming out of the GATE of each transistor, not the drain for some reason. So if I probe Q1 I get signal on the Gate and Source (probing the leg itself) but nothing on the drain, same applies to Q9.

 

[LittleRummyTumTum]

UPDATE:
So I subbed the J112 for a 2N5457, which has been a step in the right direction.

I can now get unity gain/volume if I crank the volume and boost knobs, but it sounds very gated/splatty like a dying battery or similar. Whereas with the J112 it sounded how I expected, just very quiet. I’ll go back and check the voltage coming of Q9 again when I get a chance.

 

[music6000]

UPDATE:
So I subbed the J112 for a 2N5457, which has been a step in the right direction.

I can now get unity gain/volume if I crank the volume and boost knobs, but it sounds very gated/splatty like a dying battery or similar. Whereas with the J112 it sounded how I expected, just very quiet. I’ll go back and check the voltage coming of Q9 again when I get a chance.

try another 2k4 temporary parallel with R27 Pads & see if that improves, it will give you 1k2 & increase voltage to Drain.