Gah, why can't I get a simple Fuzz face to work!

[elshiftos]

Built loads of other stuff but never got around to making a fuzz so I decided to try the BC108/9, as in this site:
http://fuzzcentral.ssguitar.com/fuzzface.php

Initially did a vero build, then tried in on breadboard. In both cases it always self oscillates when the fuzz control is turned up from about 50% onwards. Grounding the input stops the oscillation, swapping components for other types makes no difference. Also tried de-coupling the rail - nada!

Also, I notice the input impedance is relatively low and tends to 'suck tone' quite badly. Is this all part of the FF character?

Thanks

[frequencycentral]

You are using the NPN layout and not the PNP layout right? Negative earth for BC108/9.

[JDoyle]

Unfortunately, though it is a small circuit, the Fuzz Face is NOT a simple circuit. Because there are so few components, EVERYTHING matters...

1 - yes, the FF has a very low input impedence. The input of the first transistor is a diode to ground. And yes, this is a part of it's sound.
2 - the oscillation is due to the gain available and has a lot to do with layout: keep the wire runs short, the input and output as far away from each other as possible, and use a shielded enclosure. Another, additional, option is to put small caps to ground on the base of the transistors, from the collector to base of the transistors, in parallel with the collector resistors and the 100k resistor from the 2nd Q's emitter to the base.
3 - use lower gain transistors and/or find some germanium devices.

Good luck!

Jay Doyle

[elshiftos]

NPN, BC108/9 layout, neg earth, breadboard, short leads, etc.
Thanks for the suggestions, I shall take them on board and continue!

[aron]

Yeah, I usually tell people to build Gus' designs:

http://www.diystompboxes.com/pedals/gusFuzzFace.gif

[bluesdevil]

Check the pinout of the transistors, maybe?

[elshiftos]

Hey thanks for the suggestions!
I got the gus working and it sounds pretty good - it'll make a good basis for experimentation.
This will come in handy

[Marc.yo]

thats a BIG board....holy smokes.

Hey thanks for the suggestions!
I got the gus working and it sounds pretty good - it'll make a good basis for experimentation.
This will come in handy

i'll be workin on a tantulus as soon as i get home in 20 minutes...i'll do a picture based thing with clips and such. for now it'll only be breadboarded....but yea.

[elshiftos]

I got so wazzed off with all the flying leads coming out every time I moved the breadboard that I decided to copy someone elses idea and mount it on a baseplate.
It is SO much easier to work with now!

[jambers]

Hello,

I've been playing around with a ff-design in which all resistors are trimpots. And after checking Joe Davissons ff-calculator, and reading an bias article on the ff (I can't remember what exactly) I've found the following to work rather well:
- bias the collector voltage of transistor 1 to more or less .5 - 1 volt.
- bias the collector voltage with the fuzz pot full on to 4.5 to 5 volts.
- the resistor between the 2 transistors works almost like a volume-resistor. With a trimpot you can dial in to a value for which the volume is maximum.

Yesterday I biased a fuzz face with a BC107 and a BS170 very well in this manner. As well as other combinations of transistors.
With a breadboard, you can easily use trimpots and dial in to the resistorvalue that works. Once you get it up and running, measure the value of the trimpots and your set.