SOLVED Sandspur fuzz - no sound, led and bypass work

[Jedijedd]

Hello all,
This is my first post here, and probably like many new members, I have a troubleshooting question as my first post. I put together a Sandspur fuzz and have been getting no sound from the pedal. I get signal in bypass and the led works but nothing from the pedal itself. Interestingly enough, it produced sound on my first try, but the led was very weak and so was the sound. I’m not sure if there is a grounding issue or something is wired wrong.

Some of the troubleshooting things I have tried:
- tested all the values of caps and transistors which seem fine.
- tested the sweep and value of the pots which seem fine.
- tested the input jacks and footswitch
- tried different transistors with no change
- checked that I haven’t switched the input and output cables
- checked for grounding issues such as cold solder joints, bad solder joints, or bridges (I know some of this is not the prettiest but I’ve done the tug test and continuity test, however I could be testing these things wrong?)
-I replaced C3 with a new cap, as I wasn’t getting a reading but nothing has changed
- checked for any grounding issues such as metal touching the enclosure or foot switch

Things I haven’t tried or been able to figure out:
- getting correct measurements from the diode (I get a reading one way but not the other) or the electro caps. I haven’t removed them yet to get correct readings. I get values but they seem all over the place
- I haven’t been able to bias the transistors yet

I also wasn’t sure about my power supply. I have two wall warts that are center negative but one says ac/dc adaptor while the other says simply “dc”. I grabbed one thinking it was the dc one and wasn’t sure if I fried anything.

Anyway, I have been trying to get this to work for a few weeks, while also taking my time with it. This is my second pedal I’ve built, and the other one had the wrong value cap keeping it from working. I’m sure I am missing something simple here and hoped that another set (or sets) of eyes could help.

Thanks for looking and reading!

 

[Synchrony Pedalworks]

I would suggest checking you voltages at the transistors and power input to the board.

If that checks out, then proceed with an audio probe.

 

[Erik S]

Is your middle pot contacting the solder joints on the board when it's installed in the enclosure?

 

[Jedijedd]

I would suggest checking you voltages at the transistors and power input to the board.

If that checks out, then proceed with an audio probe.

Thanks, I'll give that try. Any issues with the power supplies (wall warts) I'm using?

Is your middle pot contacting the solder joints on the board when it's installed in the enclosure?

Not that I know of. I have a piece of foam in-between the pot and the back of the board. I tried to look at the whole wired setup when I installed it into the pedal for contact between solder joints and metal etc. but I could see anything touching.

 

[Jedijedd]

I've tested the transistors and if I am interpreting the readings correctly, they read as follows (I have three sets I was going to try):

BC108B: 730-722
2N2222A: 640-630
NTE123A: 655-648

These readings were arrived at by placing the positive probe on the base and moving the negative probe between the emitter and collector. I'm assuming the lower number is the voltage drop? I have not tested the power supply yet.

 

[Harry Klippton]

Your wall warts look acceptable

 

[Synchrony Pedalworks]

I've tested the transistors and if I am interpreting the readings correctly, they read as follows (I have three sets I was going to try):

BC108B: 730-722
2N2222A: 640-630
NTE123A: 655-648

These readings were arrived at by placing the positive probe on the base and moving the negative probe between the emitter and collector. I'm assuming the lower number is the voltage drop? I have not tested the power supply yet.

You test the transistors by placing the negative probe on the negative terminal for power and the positive probe at each transistor leg. It is helpful to know the voltage at each leg. The bias trimmer and Sundial will help adjust the voltages.

 

[Jedijedd]

You test the transistors by placing the negative probe on the negative terminal for power and the positive probe at each transistor leg. It is helpful to know the voltage at each leg. The bias trimmer and Sundial will help adjust the voltages.

Thank you for this! I’ve had a hard time finding such a straightforward explanation for measuring voltages. I’m still learning how to troubleshoot and use a multimeter in regards to pedal making. I’ve wired a lot of guitars but this is way more in depth. I’ll take the readings again.

 

[Jedijedd]

Forgive my noob-ness, but I am having trouble testing the transistors while connecting the ground to the negative power terminal. I don’t seem to be getting any readings, but when I do it is when I move the negative probe to ground (the enclosure). I am only getting readings from the base and collectors of both q1 and q2.

For my own clarity of understanding, when connected as you say, would I be using the diode function or voltage function of the multimeter?

Also when I have tested the transistors on there own, I wasn’t sure if was testing them correctly. I wasn’t getting similar readings between transistor legs (for example one leg would read 1 while I would get a 600 something on the other leg, while connected to the base).

I’m probably overthinking this and might need to put it away for tonight until I fully understand how to test correctly. Thanks for everyone’s help!

 

[Harry Klippton]

For my own clarity of understanding, when connected as you say, would I be using the diode function or voltage function of the multimeter?

Volts DC

 

[Jedijedd]

Volts DC

Thanks, I took those readings but will do so again, as I didn’t write them down. I’m wondering if something is up with the transistors.

 

[Jedijedd]

Well, I managed to get the meter figured out. However, with the negative probe to the negative terminal, I get no readings. If I place the negative tip on the positive terminal and positive probes on the legs I get readings. Is it possible I have the wires on the DC jack reversed?

 

[KR Sound]

Well, I managed to get the meter figured out. However, with the negative probe to the negative terminal, I get no readings. If I place the negative tip on the positive terminal and positive probes on the legs I get readings. Is it possible I have the wires on the DC jack reversed?

Can’t tell from your pics, but the longer leg on the jack is positive and the shorter one is negative/ground.

 

[Jedijedd]

Can’t tell from your pics, but the longer leg on the jack is positive and the shorter one is negative/ground.

Okay, that's how it is wired. But I will double check the wires again just to be sure.

 

[Jedijedd]

I made an audio probe today and discovered a few things. If I am following the schematic correctly, the input goes to the 50k clean trimmer. When I probed the input of the pedal, I got sound through my amp. When I moved to the next part of the schematic, which looks to be the trimmer, there was no sound. Would trimmers potentially be an issue? I turned the trimmer to see if anything happened but nothing did.

Here's the schematic: https://docs.pedalpcb.com/project/Sandspur-PedalPCB.pdf

 

[BuddytheReow]

Make sure you’re probing the correct pin. Pin 3 isn’t connected to anything which then makes the trimmer a variable resistor. Check C1. If you’ve got no signal going in there, then the trimmer is your problem. It’s most likely a bad solder joint.

 

[Jedijedd]

Make sure you’re probing the correct pin. Pin 3 isn’t connected to anything which then makes the trimmer a variable resistor. Check C1. If you’ve got no signal going in there, then the trimmer is your problem. It’s most likely a bad solder joint.

Thank you, I will give this a try. I’m still new to this, so I’m trying to do the practical component while learning how it all works. Am I following the schematic in the right way, starting from “in” and moving through to “out”? I assumed that checking with the probe and getting no sound means something might be up?

 

[Jedijedd]

Another question, will there be a difference between a single turn and multi turn trimpot in this circuit? The guy who sold me the trim pots sold me single turn ones and I didn’t know the difference at the time.

 

[Coda]

Did we ever get collector voltage readings?…

 

[Jedijedd]

Did we ever get collector voltage readings?…

No, sorry. I was going to do this today.