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!

 

[Jedijedd]

Did we ever get collector voltage readings?…

If I’m reading these right Q1 is 0.89 at the collector and Q2 is 0.24. This is with the multimeter set at 20 at the dc volt setting. I put the negative probe on the negative power input.

 

[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.

I’ve checked c1 and am getting no sound with the probe. I might try reflowing the solder later today. The joints look fine but I might be unable to see without a magnifying glass.

 

[Harry Klippton]

If I’m reading these right Q1 is 0.89 at the collector and Q2 is 0.24. This is with the multimeter set at 20 at the dc volt setting. I put the negative probe on the negative power input.

That doesn't sound right at all

 

[Jedijedd]

That doesn't sound right at all

That doesn’t sound right as in I’m taking the readings incorrectly or something is up with the transistors?

 

[BuddytheReow]

Your collector voltages are off. Have you confirmed that 9v are going into the circuit? You can confirm that for this circuit by testing both sides of D1. There will be a slight voltage drop. If they aren't close to 9v there's an issue.

 

[Jedijedd]

Okay I'll test this and report back. Thanks for the help all!

 

[Harry Klippton]

That doesn’t sound right as in I’m taking the readings incorrectly or something is up with the transistors?

It's hard to say. Either you're reading them wrong or your circuit is really really off

 

[Jedijedd]

It's hard to say. Either you're reading them wrong or your circuit is really really off

Well, as it's my second built circuit I wouldn't be surprised by either one. Just to confirm, the red probe touches the collector leg and the negative is to the negative power terminal, while the meter is set to dc volts?
I also have the transistors legs seated in pins as to not overheat them (soldered to the board). Not sure if that would change the readings.

 

[Harry Klippton]

Just to confirm, the red probe touches the collector leg and the negative is to the negative power terminal, while the meter is set to dc volts?

This is correct.

 

[BuddytheReow]

Also, this may help.

TUTORIAL Thread 'Troubleshooting 101'

Oct 25, 2021

There comes a time for every builder to spend multiple hours soldering, wiring, and breadboarding a certain circuit just to have it work incorrectly, if at all. This could happen on your first build or any build after that. This write up is to help you in your quest to figure out why it isn't working on your PCB, perfboard, stripboard, or breadboard and to provide some helpful tips when asking the community here. There is some great advice scattered throughout this forum and I thought it would be a great idea to compile my thoughts here

Items you will need to help troubleshoot in no...

• BuddytheReow
• Replies: 3
• Forum: The Test Kitchen

• 
• 

 

[Jedijedd]

Also, this may help.

TUTORIAL Thread 'Troubleshooting 101'

Oct 25, 2021

There comes a time for every builder to spend multiple hours soldering, wiring, and breadboarding a certain circuit just to have it work incorrectly, if at all. This could happen on your first build or any build after that. This write up is to help you in your quest to figure out why it isn't working on your PCB, perfboard, stripboard, or breadboard and to provide some helpful tips when asking the community here. There is some great advice scattered throughout this forum and I thought it would be a great idea to compile my thoughts here

Items you will need to help troubleshoot in no...

• BuddytheReow
• Replies: 3
• Forum: The Test Kitchen

• 
• 

Thank you, I was looking over that a bit ago but will look again.

 

[Coda]

One quick tip; when checking the collector voltages, make sure that both the bias trimpot and Sundial controls are set to noon…

 

[swelchy]

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

Are you in the US? Maybe one of us can facetime or video call you... I don't have a sandspur built but I'm sure I have a sandspur pcb I could solder up in a matter of minutes and have it working on a test platform...

 

[Jedijedd]

One quick tip; when checking the collector voltages, make sure that both the bias trimpot and Sundial controls are set to noon…

Thanks, I think I forgot to do this when checking last time!

Are you in the US? Maybe one of us can facetime or video call you... I don't have a sandspur built but I'm sure I have a sandspur pcb I could solder up in a matter of minutes and have it working on a test platform...

I’m in Canada. Thanks for the offer! It’s a very simple circuit and I have successfully wired up a sunlion last year, so I’m not sure why this one is kicking my butt.

 

[Jedijedd]

Okay so I checked the d1 spot to see if I was getting 9v and I am on both sides but I didn’t notice a slight voltage drop. It stayed a bit above 9v. I also placed the bias and sundial at noon and there was no change to the collectors on q1 and q2.

 

[Coda]

R4 is 470k. It should be 470R. That’s why your collector voltages are so low…

 

[Jedijedd]

Well that will do it! I don’t know why I ordered a 470k, I feel like such a dork. Thanks so much, I’ll look to replace that and see where I’m at. Cheers!

 

[swelchy]

I went ahead and built out a sandspur last night in case we needed to compare some values

 

[Jedijedd]

I went ahead and built out a sandspur last night in case we needed to compare some values
View attachment 83477

Thanks so much! I'll get the correct resistor today and see if that does the trick. Thanks for the help all. Great community here!

 

[swelchy]

Hard to really tell but from your photos it really looks like your power jack is wired backwards.. have you confirmed your getting positive voltage and not negative 9v?