Foxx Tone Machines - Why No Bias or Starve?

G

Ginsly

Well-known member
Many circuits have been tweaked by builders to include either starve and/or transistor bias controls- Fuzz Face, Tonebenders I, I.V, II, and III, Bosstone, Fuzzrite… Sometimes for temperature stability, sometimes for texture and gating.

I’m not sure I’ve ever seen a Foxx Tone Machine based pedal with either control… there must be some reason for that..? Maybe the octave-up part of the circuit complicates it?
 
No one's tried a transistor bias on this, huh?

If one WAS to try this, which resistor would they have to turn into a pot?
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xefned said:
I think you lose the octave effect when your transistor pairs are unmatched.
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That makes sense. It's heresy, but... I kinda like the FTM a little better without the upper octave...
GizzWizzKing said:
Could build one of these and try it with all of your fuzzes to see how they react. Still on my to do list.
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Just remembered! I have a Danelectrode variable voltage supply somewhere, maybe I'll try that on my Warm Audio FTB... Really more curious about the transistor bias, but wanna try both.
andare said:
Starving an octave fuzz will probably sound similar to turning down the guitar's volume >>> ring modulator artifacts
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I wonder what it would do in NON-octave mode, though..? I love the octave, I do - but the raw fuzz tone of the FTM is fantastic, and I'd love to see what happens with a transistor bias knob - still not sure which resistors to monkey with in the Fuzzy Fox schematic posted above...

In the meantime I'll power starve that Foxy Tone Box!
 
Ginsly said:
That makes sense. It's heresy, but... I kinda like the FTM a little better without the upper octave...

Just remembered! I have a Danelectrode variable voltage supply somewhere, maybe I'll try that on my Warm Audio FTB... Really more curious about the transistor bias, but wanna try both.

I wonder what it would do in NON-octave mode, though..? I love the octave, I do - but the raw fuzz tone of the FTM is fantastic, and I'd love to see what happens with a transistor bias knob - still not sure which resistors to monkey with in the Fuzzy Fox schematic posted above...

In the meantime I'll power starve that Foxy Tone Box!
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Try R4 and R13. You'll want to add additional resistance.
Maybe a 50k push/pull pot to move the pot from one position to the other? Add parallel resistance in the R4 position to lower the value some.
A "dual voiced" starve could be cool.
Makes sense in my brain basket anyway...
Wait, not doesn't. Would end up disconnecting one or the other.
Would work for parallel resistance but not series. At least I can't work it out without a pen and paper and am a little busy atm.
 
After some initial struggles, I breadboarded it! First time I've translated a schematic.

I hooked up a B50K (+ a 1k resistor so I wouldn't burn out the pot) to R3, R4, R13, and R19.
It had the best effect on R4, and at a resistance of around 22k it gets more zippery in non-octave mode and made the upper octave kind of bloom and splat in a different way - it also seemed to make it less present, which I actually like. Couple questions!

If I wanted to simply put two different resistors on a switch, what kind would I need? A DPDT?

And let's say I wanted to implement an overall, global voltage starve instead of the transistor bias - how would I do that on the breadboard?
Thanks for the help @jwin615 and everybody! Feels great to have finally breadboarded something by myself.
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For overall voltage starve take a B10K pot and put it between the supply and board. So red wire from supply to lug 1 and lug 2 leads to the + rail.
 
Nostradoomus said:
For overall voltage starve take a B10K pot and put it between the supply and board. So red wire from supply to lug 1 and lug 2 leads to the + rail.
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Funny, I was JUST reading about this! I saw people mention B5K - is there a benefit to using 10K? And I don't need to add a small value resistor in series with the pot to protect it?
 
BuddytheReow said:
The resistor is only to protect a diode. It's really dealer's choice on what value pot you want. I would go with a B taper. 5k, 10, 25k. Try it and find out!
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Huh... I always gathered that it's smart to add a small resistor to a lug so you don't risk frying the actual pot. Maybe that's just when replacing biasing resistors with pots? Learned that here, actually!
Nostradoomus said:
Nope you’re good
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Gotcha, thanks!
 
Nostradoomus said:
pots are resistors basically
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Right, but in certain situations you can burn the sensitive elements in a pot by simply plopping it in where a biasing resistor used to be - or so I've been told! Again, maybe that's only resistors in certain locations with higher-voltage circuits - really not sure...
 
Yikes, tried voltage starve with a 10k pot - squeal city! Not in all positions, but unfortunately happened in some of the more interesting middle spots. Dang!

It's odd, I starved a FTM with a Danelectrode variable voltage psu recently and it didn't do that at all... hmm
 
Nostradoomus said:
Could just be because its on a breadboard, they aren't the most silent prototype tool :ROFLMAO:
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Tell me about it! I had no idea there were quite so many evangelical preachers in my area... :oops: 📻

So.... how about the "putting different resistors on a toggle switch" situation? Seems like it might be easy, but looking at past threads here and elsewhere, I'm still not sure what the preferred method is... Seems like it involves an On-On-On switch, and I think I only have On-Off-On.. hmm.

Maybe I could at least switch between two resistor options instead of three? Stock and one variation? Would love some insight.

Edit: Just put two different resistors on a DPDT on-on switch! Works great. Seems like three different resistors might be tougher though...
 
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