Fuzz Face Guitar Pedal Oscillation

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I am building a Germanium Fuzz Face out of some transistors my grandad
had. Only problem is, the circuit is oscillating like crazy. I see
where the original trans were AC128 with an Ft of 1MHz. I'm using 2N65
for both trans. They also have a Ft of about 1MHz. I've also tried a
2N247 for the second trans. The circuit oscillates when I adjust the
1K pots 200kHz and higher. Gains for the 2N65's are 85 and 200. For
the 2N247 gain is 86. Anybody worked with these transistors before?
Ever had oscillation in a Fuzz Face?

Thanks,
Charlie Luke

Re: Fuzz Face Guitar Pedal Oscillation
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If you post schematics somewhere then those of us who have no idea what
a Fuzz Face is would be able to help you out.

If this is a design that worked for someone else, then chances are that
your problem isn't the design but the implementation.  Your transistors
sound like they're reasonably similar, so I'd look for things that your
particular circuit does differently than the regular model.

Are you bypassing the supply adequately?  You should have capacitors
right at the stages of interest from supply to ground, with sufficient
capacitance to keep your output stage's current draw from coupling back
to your input stage's input.

Are you using mile-long wires to hook everything up?  That can cause
opportunities for your output to couple into your input.

Post a photo if you can, with a link here, and someone will critique
your fabrication techniques for you.

--

Tim Wescott
Wescott Design Services
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Re: Fuzz Face Guitar Pedal Oscillation



http://www.geofex.com/Article_Folders/fuzzface/fffram.htm
is the link for the schematic.

The one I'm using is the one labeled "Fuzz Face with Fuller Mods".

I do have caps on the Pwr supply. 47uF and .1uF in parallel. I
probably have too much gain and need to reduce it or I need to reduce
the amount of feedback.

Thanks
Charles Luke




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Re: Fuzz Face Guitar Pedal Oscillation
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Try inserting a 75 ohm or larger resistor in series with the base of
Q1. It will increase the miller effect and probably stop the
oscillation. Does this help?

Re: Fuzz Face Guitar Pedal Oscillation
On Thu, 18 Sep 2008 15:43:37 GMT, no snipped-for-privacy@bellsouth.net (Charles

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I just built a silicon version of the Fuzz Face. Sounds OK. I
originally had some oscillation on the output transistor, which was
being caused by a bad connection. So, check your connections.

Seems the difference between the germanium and silicon version is
mostly gain of the transistors. I cut that gain back using a smaller
collector resistor on the input transistor. I'm also not quite
satisfied with the high notes, which are probably getting too much
second harmonic, and not enough boost. I'll work on it a bit tomorrow
to see if I can punch up the sound. Those monster chords sound good
through the fuzz face and my marshall, though. Much nicer than the
built-in distortion effect.

Regards,
 Bob Monsen

Re: Fuzz Face Guitar Pedal Oscillation

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If all you want to do is trash up your guitar sound, a 1N400x diode in
series with one speaker lead should do the trick.

Good Luck!
Rich


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