help! can you remove neg feedback from a germ fuzz face?

[bobster]

hi folks -
i have read that the 2 transistor vox tonebender mk 1 has no neg feedback which results in more treble and clarity.
i enjoy my home built fuzz face germanium [ nkt271 ] but dont like the woofy bass at full tilt so much.
ive tried lower i/p cap and 100k pot but wasnt really convinced with those mods.
my question is -  can the neg feedback be taken out of the FF so to allow more clarity etc and if it can , how do i do it!
thanks - rob

[petemoore]

 100k is the feedback resistor [between Q1 base and Q2 emitter.
  I belive another 100k might go next to it, making the FF feedback resistor effectively 50k.
  Notice that the output cap is often greatly smaller value than the input cap, some like the circuit 'swamped' it seems, then cut some bass out at the end, trying increasingly small input caps to reduce bassy wool produced a more 'needle like mosquito' tone, I believe the AC bypass cap is 10uf here/now.
  Breadboard ...
  Certainly matters what is input, what what comes out goes into.
  At the guitar end of the FF, SC pickups seem to work well, HB's can be muddy but brightened somewhat by using larger value volume pot with a treble bypass cap on it. With the input gain/voiced like this [I just put CTS 500ka pots in a LP, bypass cap across the signal path lugs], my LP's with HB's have a much more 'favorably varied' response and gain control [at the guitar volume], it actually cleans up and gets a bit treblier as the control is backed off...scrapes the mud off so to speak.
  All about the voicing on the input, but the input cap mods start sucking the juice out about the time they're doing anything much.
  Then there's the amp..whether it's helping the FF distort or not.
  Or more of a Tonebender type thing, add another transistor to the front of the FF +1Q = TB, then the FF circuit can get driven and voicing the bass back doesn't deflate the overall tone.
  I
   
   

[JDoyle]

Don't believe everything you read.

The feedback resistor is the 100k, as Pete said, from the emitter of Q2 to the base of Q1. Take it out of yours and see what happens. Just make sure you can put it back...

At full tilt, the gain knob all the way up, there is no signal fed back at all, only DC. The signal is bypassed to ground via the cap on the gain knob's wiper.

Without the feedback resistor there is no way to bias the circuit other than the leakage of Q1 - which is different for every transistor and will vary widely with temperature. The feedback resistor serves to bias the circuit and stabilize the bias.

In my humble opinion, what you read is flat out incorrect.

Regards,

Jay Doyle

[MicFarlow77]

Question: Rather than pull out the feedback resistor all together, what about routing it from Q1 Base to ground, instead of Q2 Emitter? (that makes sense in my head.....) You would certianly loose the feedback nature of it, but that should still enable Q1 to bias correctly....

I have a germ FF on a breadboard... might have to try this and see what happens as it will be easy to put it back if it sucks!

Thanks,

Mick

PS John, I have not forgotten about you.... will try to get to the post office soon.. PM me your address....

[bobster]

hey guys , thanks for the cool info.
i might just leave FF as is cos it works great with my strat and old non MV marshalls when i turn gtr vol down it cleans up real nice.its probably just the nature of the beast.
ive made a tonebender mk11 and its hilarious.... just mentally ill !

what im after i suppose is a middle ground between the two , a fuzz that cleans up well but at full vol is thick and sustaining but not too flabby on bass register .
do you think im after a tonebender mk1 or 1.5 ?
ta - rob

[ode2no1]

what about an mk3? or fulltone soul bender clone? it doesn't clean up the same way a fuzz face does where it bumps up the treble and gets ultra clean, but it does clean up and at full volume it has quite a bit of gain without getting all bassy. the lower gain sounds are incredible too. i really like the way my soul bender clone sounds with the gain all the way down actually. oh...thats another thing. the fuzz face just loses all clarity and usability with the fuzz knob below about 2 o'clock but the tone bender sounds good at all settings. ok i'll shut up now.

[Gus]

Try a Si based one and adjust the input cap make it smaller.

You could try this it works with different number transistors 2n2222a, 2n3904 etc.  The input cap in the schematic is for the older sounding input tuning try .1uf, .22uf, .047uf etc
http://www.diystompboxes.com/pedals/gusFuzzFace.gif

[JDoyle]

Something you could easily try that would reduce the 'woofiness' at full tilt would be to reduce the cap on the wiper of the fuzz/gain pot:

If you used the stock 20uF cap the cutoff is a little under 8 Hz which effectively means it boosts everything equally.

Changing it to 1uF moves the cutoff up to around 160 Hz which is probably a good starting point for experimentation.

For reference: an open low E string is (roughly) 82.5 Hz, the high E, 330 Hz. So the 1uF will start rolling off, again roughly, from the open D string (147 Hz) on down. (Additionally almost all pickups are unable to reproduce frequencies above about 8kHz - and we haven't even left the guitar yet; the amp and speaker combo serves to cut the range of frequencies reproduced even further.)

While at first blush this may look a bit too high in the frequency spectrum of a guitar to start the cutoff, a few things intervene to mediate that:

- lower frequencies have more inherent 'strength' or energy to them, both due to their nature and the physics of guitar strings.

- a simple first order filter, such as that formed by the fuzz pot and cap combo in this situation, is quite slow in its effect, being only 6dB per octave. (It also takes a little bit for it to hit it's slope of 6dB, thus I don't think that my mention above of the open D is actually that 'rough' of an estimation.)

- the character (or 'tone') of any musical instrument lies not in the fundamental of the note played on it, but in the harmonics it creates while playing the fundamental.

- distorting bass frequencies has a greater effect on the overall sound as the harmonics produced are more likely to fall in the range of hearing than those created by distorting higher frequencies.

Anyway, try reducing the cap on the wiper of the fuzz pot and see if that gets you nearer to what you want out of your Fuzz Face.

Regards,

Jay Doyle

[bobster]

thanks guys!
jay , that sounds like a good tip re reducing the 22uf electro. i'll give that a try and see how it works at the gig this weekend.
thanks all you fuzzheads
rob