Help navigating with audio probe

[ac30irons]

So I have built this rangemaster (done loads of these) with a NPN transistor. It WAS working. The person who I did for says there is no sound on engaging the pedal (works in bypass and led is good.)

My thoughts are to get in there with an audio probe to work out what has gone wrong (after visual checks etc.) Here is the issue, I just can’t get my head around how to follow a schematic. I know I start at the ‘in’ of the jack and then the board but where the hell do I go then. Thank god it’s only a handful of components. There is no D3, IC, C6 or C8 in this build.

If anyone could help with a road map I would appreciate it.

 

[Harry Klippton]

 

[ac30irons]

View attachment 78069

@Harry Klippton Thanks so much. How do you even work that out?

So - in, R1, C1, R3, base of Q1, Colecter of Q1, pin 1,2 and 3 of the pot, C4 and R4 out !!!

I would be jabbin all over the circuit.

 

[Harry Klippton]

I think about it like this: signal goes in at the input of course, and flows towards the output. The whole reason the transistor is there is to amplify the signal, so it's gotta go through there. Most pedals with transistors are common emitter, so the signal goes in the base and out the collector. Then it's just a matter of connecting the dots

 

[Harry Klippton]

@Harry Klippton Thanks so much. How do you even work that out?

So - in, R1, C1, R3, base of Q1, Colecter of Q1, pin 1,2 and 3 of the pot, C4 and R4 out !!!

I would be jabbin all over the circuit.

Sorry that's me scribbling with a broken hand on my phone. You may hear signal on pin 3 of the pot, but that's not where you need to be listening. Same with the other components that go to ground. You might hear some signal there but that's not where you're listening with the audio probe

 

[ac30irons]

Sorry that's me scribbling with a broken hand on my phone. You may hear signal on pin 3 of the pot, but that's not where you need to be listening. Same with the other components that go to ground. You might hear some signal there but that's not where you're listening with the audio probe

Thanks dude, super helpful. I need to attend schematic reading class I think !!!

 

[Harry Klippton]

This is the perfect circuit to get your feet wet

 

[ac30irons]

This is the perfect circuit to get your feet wet

I build loads of stuff but just haven’t invested in the technical side of things. The danger of paint by numbers guitar pedals

 

[comradehoser]

I locate the schematic with the build layout doc and follow in from the in jack or back from the out It shouldn't jump around too much. Tracing is part of learning what everything does.

 

[ac30irons]

I locate the schematic with the build layout doc and follow in from the in jack or back from the out It shouldn't jump around too much. Tracing is part of learning what everything does.

Thanks - it’s working out what’s in the audio path and what isn’t that I struggle with

 

[Ginsly]

it’s working out what’s in the audio path and what isn’t that I struggle with

Same here. I'm finally able to breadboard (some) schematics, but when things go wrong it's very tough to know what path the probe should follow. I just assumed you would probe everything after the Input and see where signal stops, but it's clearly not that simple. Every circuit is different, but there must be some basic guidelines to help determine this.

I think about it like this: signal goes in at the input of course, and flows towards the output. The whole reason the transistor is there is to amplify the signal, so it's gotta go through there. Most pedals with transistors are common emitter, so the signal goes in the base and out the collector. Then it's just a matter of connecting the dots

This is a great start, and really helpful (thanks). I guess it's the "connect the dots" that still confuses me - I would just wind up probing everything since it's all technically connected! Maybe you could expound on this a bit? I recently had an issue breadboarding a somewhat complicated octave fuzz, and stopped probing early on when the signal weakened to almost zero. Maybe that was the problem area, but since I was expecting every leg of every component to pass sound I possibly stopped too early.

 

[jwin615]

You want to "get" ax analysis.
Check around 3 minutes of this video.

He does AC analysis of a few circuits, as do a few other YouTubers. Grey bench comes to mind.
You basically ignore power stuff. Biasing resistors, blocking caps, voltage dividers.all go out the window. You're left with the "audio" circuit

 

[Harry Klippton]

Probe a known working circuit. You'll figure it out

 

[BuddytheReow]

Probe a known working circuit. You'll figure it out

Harsh truth, but he's right

 

[Ginsly]

You basically ignore power stuff. Biasing resistors, blocking caps, voltage dividers.all go out the window. You're left with the "audio" circuit

I really like how he deletes and repositions parts of the circuit in that video to help dumdums like me visualize what's going on.

 

[ac30irons]

Same here. I'm finally able to breadboard (some) schematics, but when things go wrong it's very tough to know what path the probe should follow. I just assumed you would probe everything after the Input and see where signal stops, but it's clearly not that simple. Every circuit is different, but there must be some basic guidelines to help determine this.

This is a great start, and really helpful (thanks). I guess it's the "connect the dots" that still confuses me - I would just wind up probing everything since it's all technically connected! Maybe you could expound on this a bit? I recently had an issue breadboarding a somewhat complicated octave fuzz, and stopped probing early on when the signal weakened to almost zero. Maybe that was the problem area, but since I was expecting every leg of every component to pass sound I possibly stopped too early.

Bro, I’m glad I’m not the only one

 

[ac30irons]

Probe a known working circuit. You'll figure it out

I never even thought of this A really great idea

 

[ac30irons]

Think I’m more confused

You want to "get" ax analysis.
Check around 3 minutes of this video.

He does AC analysis of a few circuits, as do a few other YouTubers. Grey bench comes to mind.
You basically ignore power stuff. Biasing resistors, blocking caps, voltage dividers.all go out the window. You're left with the "audio" circuit

 

[pbrommer]

I never even thought of this A really great idea

Sometimes the easiest answer is the obvious answer. But at least you KNOW it works. Then, you can compare the schematic from in to our and learn what happens. Oh, and if there's a POP sound in the speakers you found the V+!

 

[comradehoser]

Yeah, I don't think you should worry about probing the power side. It goes thump and whine sometimes. I did have some chips stop working momentarily, but they came back online. Part of the experience.

Keep in mind components linked to ground will be quiet on the ground side.

Just follow the components along the schematic.

Combine that with a continuity probe and a voltage probe, and you have the holy trinity of troubleshooting. I guess visual inspection, reflowing, and cleaning your board makes it a hexinity