DIY Fuzz pedal

[Off-Beat]

I'm having a go at building my first diy pedal. I am following this YouTube vid http://youtu.be/Rv5iQ_aenX8

I have it all connected exactly as it is in the vid as far as I can tell, it works however there is a real annoying hum coming through with it. I can't figure out what's causing it, any suggestions?

[Jazz P Bass]

Are you using the 'kit'?
7 Min Fuzz - $4.00 : diyguitarpedals.com.au, A shop for all diy guitar pedal enthusiasts!

I would suggest that you double check your work.

Is there a schematic that is available or a board layout please post it.

[Mark Hammer]

Two things.

1) 99.999% of fuzz effects rely on boosting the signal enough that clipping is assured throughout a substantial part of the note's lifespan. Otherwise there would be just a little blip at the initial pick attack and then everything would be normal. That boost,however, is applied to everything at the input jack, including whatever residual hum is part of the input signal. If the hum is a small part, but the circuit itself puts a kind of clamp on the maximum output signal level, then the hum will appear to be boosted more than the bigger part of the signal that bashes its head against the ceiling.

2) What us shown has absolutely no shielding against external hum sources. Have you taken care of that?


In general, the hum you get may not be a sign of anything done wrong, but rather the circuit behaving exactly as it ought to, with no hum-prevention measures taken.

[Off-Beat]

I'm not using the kit but the same parts. I fixed the issue it was a ground connection. Now it works perfectly fine however when I remove the 9v battery it doesn't give me the amps normal tone it sounds pretty weak and bad. I'm guessing if I box it and connect it up with a switch it should correctly bypass the circuit when switched off?

[J M Fahey]

Pulling the battery definitely kills it but it's still in the signal path, so now you have a "roadblock" so to speak.

Read about pedal footswitching in general and then specifically about "true bypass" because this very simple circuit NEEDS it, otherwise it's a tone sucker (VERY low input impedance) .

That said, it's a nice first (or second) project.
The sky is the limit

[Off-Beat]

Thanks glad it went well first time, I can see an addiction coming on

[Mark Hammer]

The schematic, as shown, has a 1uf capacitor on the input, with no path to ground unless there is a guitar or other pedal plugged into the input jack.

One of the problems that creates is that, if you were to attempt to bypass it, any sudden connection to that input cap would result in the capacitor discharging all the charge ithas stored up. This will make itself known via a loud pop or thump.

The solution to this near-universal problem is to run a high-value resistor from the "hanging end of the cap to ground. A value between 1M and 2M2 is probably optimal, although 470k can reasonably pass muster. The resistor will drain off any stored charge in the cap, so that, when you connect to the circuit, there won't be anything waiting to discharge.

C2 has the same potential issue, but because of the volume pot, it has a path to drain off.