Author Topic: fuzzface 'boosting'  (Read 1134 times)

add4

  • Solder Ninja
  • ****
  • Posts: 408
    • View Profile
    • gypsy jazz band in belgium
fuzzface 'boosting'
« on: November 01, 2016, 07:21:27 AM »
Hello there.

I have made a board for a classical fuzz face with a charge inverter, and the classical pot to blend two different input caps.
the two first pedal coming out of this 'design' sounded great, but i find the sound uninteresting at best if the gain is not 3/4 full or even maxed out. But I would also like to have more gain on tap and a 'bigger' wall of fuzz.

I tried adding a resistor in front of the gain pot, to increase the 'range' of the sweep and go from midly saturated to a higer saturation, but i'm not satisfied with the result. I guess the transistor is already fully saturating. Should i add one more stage then? or maybe even diodes to ground before the output?
Does anyone have experience in that?

Thanks

 

lars

  • Electron Doctor
  • *****
  • Posts: 702
  • "He drinks martinis, but all right."
    • View Profile
Re: fuzzface 'boosting'
« Reply #1 on: November 01, 2016, 07:51:33 AM »
Try using a 1kC taper pot for the Fuzz control. It does give you a wider range of control without the max-or-nothing-type bunching. You can also put a 220p - 1n capacitor between pins 3 & 2 of the volume pot. This gives a surprising amount of boost to the signal, especially the highs.
"Pig tri-tip leberkas, pork beef fatback buffalo brisket prosciutto tongue ham hamburger."

add4

  • Solder Ninja
  • ****
  • Posts: 408
    • View Profile
    • gypsy jazz band in belgium
Re: fuzzface 'boosting'
« Reply #2 on: November 01, 2016, 09:21:43 AM »
 Interesting. But I would also like to get more gain out of the circuit.
Would it be as simple as increasing the gain of the transistors ?

midwayfair

  • Electron Doctor
  • *****
  • Posts: 6866
  • Jon P
    • View Profile
    • Midway Fair
Re: fuzzface 'boosting'
« Reply #3 on: November 01, 2016, 12:27:14 PM »
First, I highly recommend reading and ABSORBING RG Keen's Technology of article. It will answer several questions you've already asked and break down the circuit in a way I'm not going to do.

The gain of the circuit is the ~8.7K total on the collector (8.2K + 470R) resistance between lugs 3 and 2 of the gain pot and the 22uF capacitor, which bypasses the 1K resistance of the pot as a whole for AC (rather than DC). Minimum gain is about 8.7x (8.7K / 1K) at minimum and whatever the transformer can spit out at maximum (when the 2-3 lugs are shorted -- this will depend on the transistor's own internal resistance).

Do a little hand math for the gain factor at each resistance value, compare it with the math for voltage gain versus dB (which is an exponential scale) and you'll see that using a linear pot requires a pretty big turn to increase the gain from, say, 8.7x to 87x (via 100 ohms of resistance between 2 and 3), which is how big you have to go to get an appreciable amount of extra gain and distortion. Where's 100R on a 1K pot? Measure it if you don't know. Now try to get to 10R (for a hypothetical 870x gain factor). You like it at 3/4 -- what's the reisstance at 3/4 on the pot? Now go grab a log pot (or reverse if you have it) and do the same measurements to see where it falls on the pot's travel.

Quote
I tried adding a resistor in front of the gain pot

This REDUCES your maximum gain, because it adds resistance between lugs 2 and 3 of the gain pot.

Quote
or maybe even diodes to ground before the output?

The output of the fuzz face (at least the classic circuit) is a voltage divider by the 8.2K between the output cap and the collector, divided by a 470R between the output cap and the power supply. The end result is you get about a half volt of output. Go ahead, plug it into a voltage divider calculator.

It sounds loud because it's a steady half volt, while we're used to a clean guitar signal maybe peaking at 1V but falling off very quickly to a much smaller voltage.

Grab your favorite diode and measure the forward voltage. That's the amount of voltage you need for the diodes to clip.

Got enough?

There are loads of posts (and again, read the Technology of) about getting more OUTPUT if you need it.

Quote
Would it be as simple as increasing the gain of the transistors ?

Well, I don't know what you're using now, so I can't say what an increase actually means. But if you want to find out, just use a couple sockets and your ears. Lots of people think that high gain transistors sound like ass in a fuzz face circuit, but they might be looking for something different.

Quote
Should i add one more stage then

Got a booster in the house anywhere? Or a breadboard? Try stuff! Experiment!
Myself's music & things I make: http://jonpattonmusic.com. My band: http://midwayfair.org. PCBs of my designs from: http://www.1776Effects.com (Bearhug Comp & Cardinal Harmonic Trem); http://www.jmkpcbs.com (Hamlet+ delay & Blue Warbler envelope vibe); Snow Day OD/Flabulanche: www.madbeanpedals.com

brianq41369

  • Transistor Tickler
  • **
  • Posts: 63
    • View Profile
Re: fuzzface 'boosting'
« Reply #4 on: October 08, 2017, 11:08:13 PM »
Schematic? Transistors?


Sent from my iPad using Tapatalk

WormBoy

  • Solder Ninja
  • ****
  • Posts: 267
  • TJ
    • View Profile
Re: fuzzface 'boosting'
« Reply #5 on: October 09, 2017, 12:56:23 AM »
The Fuzz Face is one of the most frequently discussed and tweaked circuit around, so thereís plenty of info on almost any aspect of the sound (I second Jonís recommendation for the Technology of ... article).

On the FF, I personally find the fuzz pot pretty useless, and leave it to (almost) max most of the time. I make sure that there are no buffers between my (passive) guitar and the FF, and use my volume pot to go from clean to full out fuzz. If you like more fuzz, experiment with different trannies, Ge and Si (a combination might work for you). If you still donít like, you probably donít like the FF circuit ... it happens  8). Try one of the tonebenders for more saturated fuzz (but less cleanup with the volume on your guitar).