Pork Barrel - Low Volume Output

[schrectacular]

Hello all. I recently built two Pork Barrels. The first I put into a box before testing all the lights work, but no sound at all. So I put the second one onto my tester box. It works, but the volume is really low. I got out the multimeter and checked voltages as per build diagram. There are definitely differences. The one strange one is this - measuring tester box with the +/- leads WITHOUT the Pork Barrel connected, 9.38v. With the pork barrel connected, 8.55v. This seems strange...

I have attached a pic with the voltages written against the diagram, along with some pics of the build itself. Any ideas what I've done wrong? Anything to look for would be helpful!

Thanks y'all!

[zombie_rock123]

Photos of the other side of the board/s could help. Q3 collector is odd being half supply when it's hitched directly to the power line. Did you use the same transistors as in the build doc? (I sub them all the time and can get pinouts way off if I'm not careful!).

[schrectacular]

Thanks for the quick reply. This one is easy as far as transistors go - they are all five 5088s. I confirmed on board.

Attached a pic of back of board:

[schrectacular]

Q3 collector is odd being half supply when it's hitched directly to the power line.

Ugh... I rechecked, those are actually 4.3, 3.7, 8.3 top to bottom. I was checing from the opposite sid eand must have read the middle twice...

[zombie_rock123]

Full disclosure - I'm not amazing at debugging so apologises. Really confused why the collectors ate showing slightly different voltages by more than .1ish. Have you reflowed all solder joints including the in and out pads? If so it might be time to break out an audio probe to follow the signal path (in and out of the first opamp, before and after the BBD) to see where the level disappears

[schrectacular]

I have not reflown (is that a word?) the solder yet, I'll try that today. Of course, it will be hard to get around the knobs... I don't have an audio probe but I gather they are pretty easy to cobble together. I'll report back when I've made some progress.

Thanks for the help!

[schrectacular]

I checked the soldering on all the joints and everything looks good there. Any other ideas on why I might have low volume? Could it be an issue with the blend knob? I seem to get no effect on both ends of that knob. I confirm that it's a C50k, perhaps it's just a bunk knob?

[schrectacular]

Built an audio probe and testing now - volume level is good going into and coming out of IC1 and in and out of the BBD. They seem low on both sides of the blend knob. I will poke around some more later, but for now that's what I'm hearing.

[zombie_rock123]

I'd check the resistor values of the four resistors around the Blend pot (2x 27k, 2x 20k - my phone screen is terrible so think theyre fine) - reflow those if not already and the blend pot pads and then see if any difference. If not then I'd check the audio signal at the emitter of Q3 and if it's nice and chorusy it could be a bad pot.

I'm hoping someone would jump in if I'm giving you crap advice by the way! It's what I'd do anyway. Did you tweak the bias pot with it blend all the way to chorus side? Sorry if it's a daft question.

[schrectacular]

You sexy beast of a man!!! Thank you SO MUCH for your encouragement and ideas - I traced the signal path back from output and lo and behold YOU WERE RIGHT! It WAS a wrong resistor. R12. I had 470k. That's a lot of k's different from 470R. Replaced and she'd golden.

Now that I have the audio probe I think I should be able to trace the other pedal too (all the lights work but no sound).

I definitely wouldn't have solved this without your help. Thank you so much.

[zombie_rock123]

Sterling work dude, nicely done! No better feeling than the debugged ones firing up!

Yeah audio probes are fantastic, almost feels like cheating following the signal from jack to jack and finding cold solder joints etc that way!

[schrectacular]

Dude totally! You fixed my other pedal too! I traced the circuit, turns out C2 wasn't soldered right. Man that audio probe is the dogs bollocks. So easy.

Thank you, internet stranger!