Dr. Phybes Volume drop (solved)

[Anonymous]

I just finished populating the Dr. Phybes PCB and it sounds great! One problem though, when I engage the effect there’s a big volume drop. It’s way below unity volume. I looked over the PCB multiple times, looks like all the resistors are the correct value and there are no solder bridges or funky solder joints that I can see. I checked the voltage of Q5 (which I think is responsible for boosting the output, but I’m not sure.) I get the following values:

Pin 1: 5.01v
Pin 2: 3.71v
Pin 3: 4.09v

I have the PCB hooked up to my test rig. Any ideas?

[Anonymous]

I accidentally posted two of the same pic… here’s a pic of the back. I know my soldering skills aren’t the best, but there don’t appear to be any accidental bridges or bad joints. And again, pedal works and sounds good, it’s just the volume issue.

Also, I used a B500k pot instead of A or C because that’s all I had. But that should only affect the rate change sweep, not the volume, right?

[Billy]

It’s very difficult to make your resistor colour bands out even zooming in

I’m not 100% on your Q5 pin numbers post voltages as Collector Base and Emitter for clarification

What PNP transistor did you use for Q5

The original pedal is just a shade below unity

Some of your solder joints do look slightly crumbly and dull and there’s a few ball like joints that may be dry inside so I’d try reflowing those

The pot just controls the oscillation speed so as you say won’t affect volume

Post voltages for all ICs and transistors that may indicate your problem area

If you have an audio probe, probe IC1 pin 6 and both sides of R17 and 18 and the base of Q5 to see if there is any noticeable difference in signal level

 

[Anonymous]

Thanks Billy, I appreciate your help! The problem ended up being in my test rig. No idea why. But I wired the pcb as it will go in the pedal and it works fine. Never had a problem with the tester before, but now I’m going to have to test the tester and get to the bottom of it.

Thanks for the troubleshooting tips. This was my first time posting here or in any pedal-building forum and now I’ll now what info to provide next time!

[Billy]

Good to hear it’s sorted

Funnily enough I was going to mention your test box I’ve had problems with mine in the past and we couldn’t fully see it then I thought nah!

I could tell you a few stories about my test box and audio probe failures but I won’t haha

I’ll just say it took me over a week to suss an audio probe failure which resulted in an amp being taken apart

I used an old guitar cable to make the probe plugged it into one of the amp inputs and it wouldn’t go in so after trying to force it in I used the other amp input and the probe still didn’t work

Long story short after stripping the amp down thinking I had a jack socket problem and finding I didn’t, I eventually looked at the probe / guitar cable  where the jack tip had snapped off and stuck in the amp input socket

I more or less accidentally looked at the cable end to find a problem I’d never have looked for I mean you don’t expect a metal jack tip to break off do you?

So we’ve all been there in my case more than once

[Author]

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