Audio probe questions

[Adamo]

I'm having a blast debugging a couple of pedals (one old, one new build) with an audio probe. I have a couple of questions: is it normal when using a probe and touching one leg of a resistor that you get a loud, clear sound passing but on the other leg it is much quieter?

Also, when probing a transistor, it seems like I get 'sound' when touching the base but not on the collector or the emitter. Is this expected?

[armdnrdy]

Is this the A8 that you're audio probing?

[Adamo]

No, not yet. Coincidentally, I just finished a GGG FoxxTone that's not working either so I'm starting with that one. I'm pretty new at this stuff and I suspect I have some cold solder joints. I'm going to debug the A8 next. The audio probe is a pretty neat little tool.

[Adamo]

I'll simplify my question--------when testing components with an audio probe in a 'working' pedal, should I get 'sound' on all legs of all components on the board? And...should the sound be of the same volume?

[armdnrdy]

No and No.

Post a schematic or a link to what your debugging..and we'll clue you into where you should probe to find the signal.

[Adamo]

Here's the schematic for the Ampeg A8 analog delay . Supposedly this Guyatone is the same schematic:

https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/Guyatone%20-%20PS-006%20-%20schematic.jpg

The pedal is giving me a clean signal when the pedal is engaged or not. No delay whatsoever. I wiggled and checked all components. Led seems to work properly.

[GibsonGM]

The volume drop after a resistor is normal.   If you touch power, you should get a *click*, too.  You are using a cap in series with your probe, right?  Just asking....it blocks DC and allows only what we're interested in, the audio, to come thru.     

At a working transistor, I'd expect signal at the base, and also at the collector (or emitter if it is wired with E as output, Q2 on the Guyatone), maybe a very low signal at E anyway.    I think NO signal on the collector = a problem in that area. 

Why don't you draw in with red the signal path you are probing, mark it as you go?  The re-up the pic where it stops, and you should be quite close to where your troubles are! 

[Adamo]

I'm actually get some great help on this issue right here:

http://www.diystompboxes.com/smfforum/index.php?topic=108906.0

I feel bad having 2 threads going for one issue.

[GibsonGM]

Oh, that's no good, busted!!  LOL.   J/K

Cool, you'll get it sorted out over there, looks like you're well on your way.