Fuzzface darkness. Will this fix it?

[brett]

Hi
Like many people, I find the Fuzzface too dark.  There are many mods that reduce the bass (reducing the input cap to 0.1uF, changing the output pot to 100k), but none boost the high-end.

Here's my idea:  split the 100k feedback resistor into 2 x 47k and place a 0.0033uF cap to ground between them.  That gives a roll-off frequency of about 1000 Hz.  I figure that rolling off the feedback should boost the treble.

I also notice that Roger Mayer's classic fuzz uses a small (5k) resistor on the collector of Q1.  Does this help prevent the loss of treble?  (by reducing Q1's gain)
cheers

[Stephen]

better yet just make it just a 47k with the cap... less feedback should produce a cleaner sounding fuzz with more sustain!!

I think ....my three germ fuzzes use a 22k....

[brett]

Hi
Because the feedback is into the base of Q1, I think I need plenty of resistance on the base side so that it doesn't provide a low-resistance pathway to ground from the base of Q1. 

So I might try: Q1 base - 100k - 0.15uF - 1k - Q2 emitter
That should keep all the DC bias, input impedance, etc the same, and still roll off the feedback above 1kHz.
If the gain is too low, I'll replace that 100k with 47k (which several people seem to like).

I note that in Roger Mayer's Axis fuzz, he has a capacitor that rolls off high-frequency feedback.  It's that 0.1uF cap that sits across the wipers of the "drive" pot.

I should have a build report by Saturday (curse those corporate slave-drivers that make us Fridays).
All comments welcome.

[slacker]

you could try using the Vox tone bender component values, there's a schematic in the Geofex technology of the fuzz face article.
I've got the newish reissue germanium version and that's got enough treble to make your ears bleed 

[WGTP]

Don't know much about it, but I thought there was a by-pass cap across the output pot on one of RM's that I saw.  Is that the one your talking about?   

[Meanderthal]

 I think he means this(from the schematics link above). It's basically a bright fuzz face.

http://www.diystompboxes.com/pedals/tbV829.gif

[Meanderthal]

 Or just replace the output cap with a lower value. That seems to be the main thing the voxface does different.

[petemoore]

http://www.diystompboxes.com/pedals/tbV829.gif
  This schematic looks like the 1k and 47k [top and top left R's], got their values mixed up, the 47k should be the collector resistor for Q1.

[WGTP]

http://www.geocities.com/CollegePark/Library/1355/rmclassicfuzz.gif

Here is the one I was thinking off with the by-pass cap at the output pot.  Wouldn't that boos the highs?   

[Meanderthal]

 I might be wrong but it looks like that cap allows you to preserve the highs as you turn the volume down- kinda like the strat mod. Yeah, that might  help out. Keep in mind that the fuzz is creating "highs" (harmonics) anyway, but can get drowned in mud, so the cap might let more of them get through.

[WGTP]

Yes, it should work more the lower the output is, and none at full output.   

[Meanderthal]

Bret- I may be mixed up, but wouldn't a cap to ground between resistors be a lowpass filter? Seems to me that would make it sound even darker. Maybe a resistor to ground between caps (highpass) would roll off the bottom in the feedback loop for you?

[WGTP]

Since it is in the negative feedback loop, it works in reverse, except the FF circuit is sort of wierd, I'm not really sure.   

[slacker]

I think he means this(from the schematics link above). It's basically a bright fuzz face.

http://www.diystompboxes.com/pedals/tbV829.gif

I actually meant this one http://www.geofex.com/Article_Folders/fuzzface/fftech4.gif but they're basically the same, apart from the error Petemoore mentioned. Mines basically the same as the Geofex one but it's positive ground with PNP germanium trannies. From memory Q1's collector resistor is 6k8 and It doesn't have the 47K resistor across the output pot , but the circuit board has pads and holes for it.

[Meanderthal]

 Hey, thanks for the feedback loop tip! I was kinda suspecting this might be so...
I know what you mean about the Fuzz Face being wierd. Every time I mess with mine I wind up just making it fart and crackle when I expected something cool. There's so little in there it seems that every little part value change has a drastic effect. I built the neg. ground pnp version, which I hear is even more touchy. The trannies I got from smallbear spoiled me rotten. If I use (carefully selected)ac128s it sounds good, but those big TI trannies from smallbear REALLY sound fantastic with the values he sends along. They seem to be custom- tailered to the pair he sends you, so my res. values probably won't work well for someone else. But they made it sound the way I imagined a fuzz face SHOULD. Well, I also had to mess around with the input and output caps.
Yup, it looks like you guys are right about the pnp schematic for the tonebender having the bias resistor wrong! But it's the input and output coupling caps that make it a treble booster.

[WGTP]

I have also seen diode in the feedback loop, but not sure how it sounds.

[Fret Wire]

I also notice that Roger Mayer's classic fuzz uses a small (5k) resistor on the collector of Q1.  Does this help prevent the loss of treble?  (by reducing Q1's gain)
cheers

You mean this shematic? I've never heard how this version sounds.
http://www.geocities.com/CollegePark/Library/1355/rmclassicfuzz.gif

This version I'm familiar with, I've had one for over 20yrs.
http://aronnelson.com/gallery/Schematics-etc/RM_Classic_Fuzz

It's definately brighter than a stock Dallas Arbiter . Maybe with the addition of a 100k volume, it might do the trick for you.

[brett]

Hi
thanks for all of the comments.
Yeah, I wanted to add a low-pass filter to the feedback loop, thereby increasing hi-end gain.  Ideally, the filter would be a notch between about 1 khz and 10 kHz, because bypassing really high frequencis might encourage oscillation.

However, as I went to install it, I found that this Fuzzface had a 33k resistor in the feedback loop.     No wonder it was dark.  As soon as I put an 82k resistor in there, the top end was improved dramatically.  So I didn't try the filter.  (82k is my compromise between the standard 100k and the 47k favoured by some folk.  It seems to work well.)

A Japanese 2SBsomething with hFE of 65 for Q1, and an AC188 with hFE=105 for Q2 sounded great.  In fact, virtually all my germanium devices sounded good, including every AC188 (of about 20) and all but one 2SB(324?).  (these devices were all pre-selected for hFE > 60 and <150, and most had leakage <120mA.)

thanks again

[mac]

Here's my idea:  split the 100k feedback resistor into 2 x 47k and place a 0.0033uF cap to ground between them.  That gives a roll-off frequency of about 1000 Hz.  I figure that rolling off the feedback should boost the treble.

I built a 2SD352 version sometime ago, the complementary of the 2SB342 you have if I am not wrong. I did what you suggest to increase the high end because the transition freq of these transistors made it sound dark.
When I finally found a couple of 2N388 T.I., I went the opposite way. I added a Ge diode in the junction of the 47K to increase the low end because these transistor are really bright.
Finally I decided not to use the diode and keep things as close as the original schematic.

BTW, add a couple of small caps from Q2 emitter to Q1 base, with a variable resistor from the junction of the two caps going to gnd and you have a wha inside the FF



mac

[WGTP]

http://www.geocities.com/tpe123/folkurban/fuzz/fuzzyfaces.html

At the bottom, is a version similiar to what you suggested.