Fuzz Face Clone Input and Output biasing controls

[Bassman203]

To add input and output biasing controls to this fuzz face circuit, would I replace the 100k and 500k resistors with pots?

Also, I was thinking to use these transistors. Are they a good choice?

Transistor Pair, The Fuzz Face PNP, SINO
Two matched, old-stock 3AX31C, tested in the Fuzz Face circuit. Supplied with list of resistor values used. Will also work in Bear Face, "Two-knob" Tone Benders, "69", Fuller Mods, etc. http://www.smallbearelec.com/Detail.bok?no=680

Lastly, are the input and output capacitor values already optimal for bass response, or should I increase their values?

This is the site that I got the idea of having input and output biasing controls from.
http://happyrobotmusic.blogspot.com/...fuzz-face.html

[rcubed]

The input cap is fine but you'll have to change the output cap to a larger value. Replace the 8.2K resistor on the second transistor with a 10K pot. Leave the 100K resistor alone or experiment with different values. If you do change that to a pot, make sure to add another small resistor in series so you have a resistive floor (maybe use a 20K resistor in series with a 100K pot). An output pot of 500K should be fine.

[Pitbull Growl]

Originally Posted by Bassman203

To add input and output biasing controls to this fuzz face circuit, would I replace the 100k and 500k resistors with pots?

Also, I was thinking to use these transistors. Are they a good choice?

Transistor Pair, The Fuzz Face PNP, SINO
Two matched, old-stock 3AX31C, tested in the Fuzz Face circuit. Supplied with list of resistor values used. Will also work in Bear Face, "Two-knob" Tone Benders, "69", Fuller Mods, etc. http://www.smallbearelec.com/Detail.bok?no=680

Lastly, are the input and output capacitor values already optimal for bass response, or should I increase their values?

This is the site that I got the idea of having input and output biasing controls from.
http://happyrobotmusic.blogspot.com/...fuzz-face.html

Sure, you can replace the resistors w/pots for biasing... works for zvex.

As for I/O cap values... I'd socket the output cap and grab a few bucks worth of orange drops in various values and see what sounds best to your ears (poly film caps are cheap, so experiment). For the input, you could try a 100K pot as a variable resistor w/lugs 1 & 2 wired to a 2.2 and a 4.7 uF electro cap respectively. This way you have variable input capacitance for added versatility.

Can't comment on the trannies, never tried 'em myself. I prefer the harshness of Si trannies for the most part.

I'm sure others will chime in w/their ideas and exp. as well. HTH and good luck.

[rcubed]

Also read up on this website: http://fuzzcentral.ssguitar.com/

Just about every boutique builder uses some sort of mod based on that website for their Fuzz Face clones.

[Bassman203]

Ok, I'll take a look at that.

I assumed I would use carbon film resistors, but the site you sent said the original used carbon composition. What would you recommend?

[sonicvi]

Originally Posted by Bassman203

To add input and output biasing controls to this fuzz face circuit, would I replace the 100k and 500k resistors with pots?
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The 500K resistor already is a pot, it's the volume control. The 100K the feedback bias resistor and doesn't need changing. You could increase the 2.2uF cap with 4.7-10uF and/or the .01uF with .047-.1uF for more low end.

[Bassman203]

Originally Posted by sonicvi

The 500K resistor already is a pot, it's the volume control. The 100K the feedback bias resistor and doesn't need changing. You could increase the 2.2uF cap with 4.7-10uF and/or the .01uF with .047-.1uF for more low end.

Thanks for pointing out what I didn't notice stupidly (honestly, not sarcastically), but what would you change then to make a input bias and output bias? As suggested in the link at the bottom of my first post

[coldcraft]

Never heard of "Input Bias" or "Output Bias".

Bias typically applies to the DC operating conditions of a gain element, be it an op amp, transistor, FET or Tube. If you order those transistors from small bear, I believe he will give you some notes on what value resisters to use in order to bias the transistors correctly.


The 500k resister symbol is actually a pot/knob already. Use an Audio Taper for this. I would not mess with 100k. For an input control I would probably put an pot configured like the output on the input. Guitar to lug 3, wiper to effect in, and lug 1 to ground. Try 100k, 250k or 500k. This may not do much, as you already have the gain control.


Your link suggests the info is here, http://www.geofex.com/Article_Folder...ace/fffram.htm

A great Article written by RG Keen. However there's no mention of input/output bias.

[sonicvi]

I think by input and output bias mods he's essentially referring to the Fulltone '69 mods.

[MAMMOTHvolume]

Originally Posted by sonicvi

I think by input and output bias mods he's essentially referring to the Fulltone '69 mods.

+1 replacing the feedback resistor with a 47k and 100k pot in series is also a nice mod and works like a gate control.

[rcubed]

I definitely recommend the input pot (100K) if you have an active bass. It will help out with impedance issues. I prefer the Axis Face mods myself.

[Bassman203]

Thanks for that schematic, that'll help a lot.

So, I should use a 100k instead of 50k (like in the schematic) for the input pot? And I do have a bass with active electronics.

Also, is what mammoth is saying that I can replace the 100k resistor with a 47k resistor and 100k pot to create a gate-control like thing? Just want to clarify in case I'm not following. How/where would I wire the lugs of the pot and resistor?

[rcubed]

Originally Posted by Bassman203

Also, is what mammoth is saying that I can replace the 100k resistor with a 47k resistor and 100k pot to create a gate-control like thing? Just want to clarify in case I'm not following. How/where would I wire the lugs of the pot and resistor?

For a lack of a better term, that's the Woolly Mammoth mod. You can also get a gated effect by voltage starving the second transistor with a pot.

[Bassman203]

Does this look right?
Specifically, do the pots I added seem wired correctly?

[MAMMOTHvolume]

yeah looks great i'd recomend a 2k pot for the gain control aswell and also try out a few different bypass caps - larger values = more bass / smaller values = treble boost.

[Bassman203]

Sorry, but which one is the gain control and which cap is the bypass one?

And in the drawing, what does 2ouf stand for? I know uf is micro farads, but I've never seen an 'o'

[Bassman203]

Bumpity Bump

Anyone want to answer the questions in the post directly above?

[rcubed]

That's definitely 20uF. The gain/fuzz pot is the 1K coming from the emitter of Q1. The input 2.2uF cap is fine. Play around with the value of the output cap. It helps if you use a schematic with part numbers, i.e. R1, R2, C1, C2, Q1, Q2, etc.

[MAMMOTHvolume]

yeah the bypass cap is the one coming of the gain control going to ground also.

[Bassman203]

This should be my finalized plan