I had a similar problem with my last build. Here's what it boiled down to for me -
1. make sure the 100R is 1k - it has to do with the PT2399 locking up
2. check the 330K behind the voltage regulator - mine drifted in value
3. check the 1meg from pin 7 on the opamp
In bypass. everything was fine, but no signal at all with the effect on. I found that when I touched the back of the PCB in the output path, I got hum .
I also a - touched up my solder connections
b - checked every solder joint and trace for continuity and solder bridges
The end result was #3 above
#2 above took care of my voltage readings
Hope this helps. I was very pleased with the build once it was working.
Hi thanks for your input
Can you clarify what you mean by checking the 1M and the 330K? Do you simply mean checking their resistance is accurate?
I did indeed use a 1k rather than the 100R resistor mentioned.
Yes, that's what I meant.