RAH Vero build: No gain

[AntKnee]

All EQ controls and Master working, but the gain is not functioning. With the gain off, I get clean signal, but it quiets as I turn up the gain. I've already checked wiring, components and whatnot. Here are my voltages:

Q1: D= 9.02 G= 0.12 S= 0.00
Q2: D= 5.90 G= 2.61 S= 3.13
Q3: D= 5.90 G= 2.63 S= 3.15

I though Q1 numbers looked odd, tried swapping another BS170, same result.

Schematic attached.

[TGP39]

What zener diode are you using for z1 and is it oriented the correct way?

[TGP39]

I've been trying to learn more about this circuit today. Since Q1 is a BS170 (N channel JFET), then the gate regulates the flow of electrons through the N channel. Since your gate voltage is practically zero, no or very little current will flow through the JFET. It looks like the only reason you have 9 volts on the drain is because it is directly linked to the B+ voltage source (though I am not positive about this). So the question becomes why do you have no voltage on Q1 gate?  Perhaps your bias voltage is not hooked up properly?  Do you get any voltage readings on R1? Or Z1? Also, could you get a voltage reading on pin 1 of your gain knob? (Turn the gain knob to 9:00) when you take this reading.     Hopefully, we can get this circuit fixed because I would love to hear it.    Steve.

[AntKnee]

Thanks, Steve!
I am using  9v1 zener diodes for both.
I measure 0.11 on pin 1 of the gain pot. One the diode I am getting 0.11 (cathode) and 0.00 (anode). R1 is also measuring 0.00.

[TGP39]

Ok. You're not getting any bias voltage. I want you to check that R17 and R18 are the correct resistors. Also check that C10 and C14 are oriented properly and are the correct Caps. Steve.

[AntKnee]

Ok. You're not getting any bias voltage. I want you to check that R17 and R18 are the correct resistors. Also check that C10 and C14 are oriented properly and are the correct Caps. Steve.

Thanks, again. I appreciate your help so much.
I verified my resistors are correct. I did not have a 62k, so used a 56k with a 6.8k (62.8k total). Caps are the right value and orientation. I also hit these all with a the tester. I have 9v at C10 and 5.16v at C14. I have 9v at R17 and 5.16 at R18.

Here's a pic and the layout, if that helps. (Note: I have an extra row at the bottom for a ground bus.)

[TGP39]

Anthony, you have two 22nf box caps (223j100) on the upper left hand side of the board. These two caps should be 2.2nf (222j100). I still don't think that is the issue, but let's change those caps to the correct part. Steve.

[AntKnee]

Son of a biscuit!
Ok. Installed the 2n2 caps and rechecked Q1 voltage, no change.
I notice that the layout has 4 1M resistors, but I can only find 3 in the schematic. (R1, R2, R3). Not sure if it matters, but something I just saw.

[TGP39]

This is something Ivlark says about the gain control:
     The gain pot in this is effectively a pre-gain volume control (attenuation). It dumps signal to ground in the same way and in the anti-clockwise position only the 22K resistor is stopping the whole signal being dumped to ground. So the more you rotate clockwise, the greater the signal you hit the gain stages with. Are you sure the mosfets are ok? If you've socketed them it may be worth just swapping them to see if any have been damaged. They are very susceptible to static.

     Want to try swapping Q1?

[TGP39]

Also, do you have a track cut beneath the far left 1M resistor? That one is easy to miss. Steve.

[TGP39]

Also make sure the link right next to Q1 is correct. I can't tell, but if that link is one notch lower, that will steal away your bias voltage from Q1 and pin1 on your gain pot. Steve.

[AntKnee]

I have tried swapping the FET, with same results. I actually swapped Q2 and Q1, and got identical results in both positions from the swapped FETs, so I feel confident that they are both functional in both positions.

I do have the cut beneath the 1M resistor, and my link next to Q1 appears to be correct.

Steve, thanks for all your help. You've really gone above and beyond on this. I'm going to recheck everything tomorrow with fresh eyes.

[TGP39]

Hey Anthony, helping you helps me learn as well. I'm going to try and build this and see if I can learn much more about this circuit. I wanted one of these pedals anyway. If you get the chance, take a picture of the flip side of the board. I'd like to see your pot inputs and see where they go. Keep me posted. Steve.

[AntKnee]

Hey Anthony, helping you helps me learn as well. I'm going to try and build this and see if I can learn much more about this circuit. I wanted one of these pedals anyway. If you get the chance, take a picture of the flip side of the board. I'd like to see your pot inputs and see where they go. Keep me posted. Steve.

Success!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I honestly am not sure where the problem was, but I knifed my cuts for the third time, and scraped every last millimeter of bare board on the bottom side and somewhere it fixed a short. I am up and rocking! It sounds great!

Steve, thank you again.

[selfdestroyer]

Glad you got it going. If you get a few minutes can you post your voltages now that you got it working? I have one of these boxed up that I was pretty underwhelmed by and would love to see how far my voltages are off.

Thanks
Cody