Expert Pedal Building Advice Needed

Fibus · Post by **Fibus** » Mon Jun 30, 2008 8:49 pm

I built my first ever pedal and its broken. Its a tubescreamer from General Guitar Gadgets I'm not sure if anyone has any experience with them but the volume on mine is screwed as you can see from the video below there is a huge volume drop when the pedal is on and also if i turn the volume up full it just cuts out completely.

[youtube][/youtube]

I talked to Mike and he gave me some great advice (thanks Mike). I checked the lugs on the pot when i got home and everything seems to be fine with them they are not touching the case at all. I also checked the soldering on the pcb and everything seems to be fine and measured the pot with a multimeter and it all seems to be ok. So does anyone have any ideas? Cause i am all out of them.

Here is the schematic (its a pdf)

Any help or advice would be greatly appreciated because this is kind of putting me off starting another pedal project. Thanks.

r40f · Post by **r40f** » Mon Jun 30, 2008 9:25 pm

by any chance is the pot wired to a capacitor or are the posts wired to some incorrect part?

Ninja Mike 808 · Post by **Ninja Mike 808** » Mon Jun 30, 2008 9:37 pm

So, the pot might be moving something loose when you crank it up...
Also, make sure the pot isn't wired backwards (though I doubt it is).
Maybe, they gave you the wrong pot?

Find some people who've built it already, though...

Post by **Mike** » Mon Jun 30, 2008 10:05 pm

I think now is the time to sanity check all the PCB traces with a multimeter unfortunately and go from there.

r40f · Post by **r40f** » Mon Jun 30, 2008 10:39 pm

Mike wrote:I think now is the time to sanity check all the PCB traces with a multimeter unfortunately and go from there.

yeah, if it's not something obvious, you just have to do that

Ninja Mike 808 · Post by **Ninja Mike 808** » Mon Jun 30, 2008 11:06 pm

Good luck.

Will · Post by **Will** » Tue Jul 01, 2008 1:29 am

Build a signal tester - they're fantastic tools for quickly debugging.

Post by **Mike** » Tue Jul 01, 2008 8:09 am

DuoSonicBoy wrote:Build a signal tester - they're fantastic tools for quickly debugging.

Can you link us up with some info on these?

Ninja Mike 808 · Post by **Ninja Mike 808** » Tue Jul 01, 2008 8:21 am

Is a signal tester also called an audio probe?

Post by **Doog** » Tue Jul 01, 2008 8:25 am

Mike wrote:
DuoSonicBoy wrote:Build a signal tester - they're fantastic tools for quickly debugging.
Can you link us up with some info on these?

www.fender.com
www.marshallamps.com
www.planetwaves.com

Seriously though, what does a signal tester do?

Post by **Mike** » Tue Jul 01, 2008 8:27 am

You're an idiot Doog.

I mean those probes you can use to probe any point WITHIN a circuit rather than just the output. When you build complex circuits sometimes that shit doesn't work first time. I don't have an Oscilloscope.

I want one badly, but until I have a workshop I have no space for one.

Post by **Mike** » Tue Jul 01, 2008 8:29 am

http://www.radiomods.co.nz/audioamp.html

Is this the type of thing we're talking? LIke a small board mounted audio Amp?

Fibus · Post by **Fibus** » Tue Jul 01, 2008 8:44 am

r40f wrote:by any chance is the pot wired to a capacitor or are the posts wired to some incorrect part?

Its wired to the pcb, i'm not sure what you mean by posts though.

Ninja Mike 808 wrote:So, the pot might be moving something loose when you crank it up...
Also, make sure the pot isn't wired backwards (though I doubt it is).
Maybe, they gave you the wrong pot?

Find some people who've built it already, though...

The pot isn't loose, its a tight as it can go and all the soldering on it is solid. I don't think the pot is the issue though since this is the second one i have put in and its getting the same issue. It appears to be a correct pot as well.

Mike wrote:I think now is the time to sanity check all the PCB traces with a multimeter unfortunately and go from there.

I was afraid you were going to say that. I'll probably try and use the schematic to narrow it down to the level area at least hopefully that should make it easier

As for audio probes i did come across this:

Audio Probe

Un autre diagram

Which may be something i will try out

Post by **Mike** » Tue Jul 01, 2008 8:47 am

Nice one, I'm going to build one of these definitely:

Ninja Mike 808 · Post by **Ninja Mike 808** » Tue Jul 01, 2008 10:20 am

Yea, audio probes are my best weapon.

Post by **Mike** » Tue Jul 01, 2008 10:27 am

I need to get some sodding crocodile clips, they're so useful.

NickS · Post by **NickS** » Tue Jul 01, 2008 11:59 am

Is the pot soldered to the PCB? If not, I'd try bypassing the output buffer - take the wiper (centre tag) of the pot straight to the output and take the tag that's connected to Vr and connect it to ground instead.

If the pot's screwing up the bias of the output buffer due to a solder bridge or uncut track, that should take it out of the loop.

Post by **Mike** » Tue Jul 01, 2008 12:11 pm

or just take the pot out of the equation, assuming it's after a coupling cap just take what was going to Lug 1 of the pot and connect that to the output connection on the 3PDT. How is the volume then?

Fibus · Post by **Fibus** » Tue Jul 01, 2008 9:23 pm

Mike wrote:or just take the pot out of the equation, assuming it's after a coupling cap just take what was going to Lug 1 of the pot and connect that to the output connection on the 3PDT. How is the volume then?

The pot is soldered to the pcb. But i will definitely be trying this at the weekend hopefully it will do the trick, though i have a suspicion that the problem is at the pcb level.

Post by **Mike** » Tue Jul 01, 2008 9:27 pm

Yeah, I've never done PCB mounted anything before. I would be nervous of that. Definitely understanding now why you have that 90% then nothing issue. MUST be related to the PCB.