Professor Tweed preamp cannot bias one of the JFETs

[nicolasseveryns]

Hi, I'm very new at this hobby. This is my fifth 'build'. It's the ROG Professor Tweed JFET preamp. It's a preamp driven by 3 JFETs.

I have breadboarded the preamp according to the schematic, biased all 3 JFETs at 4.5V and everything worked great. Then I decided to solder it onto stripboard according to a verified layout I had found on the the tagboardeffects blog. I managed to bias JFETs Q1 and Q3 to 4.5V. Q2 however keeps giving me a reading of 200mV. Turning the trimpot does not have any effect at all. I am measuring the voltage between ground rail and the drain pin. Doing the same with the other JFETs gives me 4.5V. The circuit however, seems to work. I get a nice tone out of it, only at overdriven settings it clips too early. I have checked all the connections, followed the signal. Everything seems to be fine, apart from the fact that I have made a mirrored build (beginner...).

What are my options? Trying a new build? Put everything as is in a pedal box?

My main question is why I managed to bias it on the breadboard and why isn't it biasing now?

Here are some pictures of the top, bottom of the finished stripboard, as well as a pic of the layout I based myself one.

Thanks for any directions/suggestions!


Top side

 

[pbrommer]

My guess is that you might have missed a cut on the strip board or missed a connection to q2. If you have a meter that can do continuity testing (beep), check to see if there is a connection from the leg of the trimpot that isn’t connected to V+ (+9V) to the drain of Q2. No connection would mean there’s something not connected to the trimpot. If it beeps, then maybe a bad Q2 or wrong pin directions?

Edit: second look you might need to make sure that 2 of the trimpot pins are connected.

Hopefully that gets you on track.