Fuzz Face - output won't go past 700mVpp??

[waspclothes]

Hey guys,
I recently built a fuzz face clone using germanium transistors from smallbear. Everything seems to be working, but the output seems to be limited to about 700mVpp.

Previously I was using a tele with single coil pickups that max out at about 300mVpp, so using the fuzz face was great - it provided the dirt and a volume boost.

Recently I switched to a guitar with humbuckers that output about 800mVpp and the FF still outputs a signal maxing out at 700mVpp, just now with more clipping. It's like it hits a brickwall at that amplitude.

Is this just a reality of the FF circuit or is there something wrong?


FWIW, when I engage the FF - the guitar input signal gets bogged down considerably to like 80mVpp.

[The Dude]

Not sure exactly what you built, but here's an explanation of how the basic circuit works. It may answer your questions.

The Technology of the Fuzz Face

If you look towards the bottom of the page in the section " Mods and Magic", there are tips on raising the output gain.

[waspclothes]

Not sure exactly what you built, but here's an explanation of how the basic circuit works. It may answer your questions.

The Technology of the Fuzz Face

If you look towards the bottom of the page in the section " Mods and Magic", there are tips on raising the output gain.

Thanks for the reply, I've just built the standard fuzz face circuit - I'll double-check but I don't think I made any modifications to it. I'm just wondering if that 700mVpp hard limit is something that all fuzz faces seem to have.

[J M Fahey]

Hey guys,
I recently built a fuzz face clone using germanium transistors from smallbear. Everything seems to be working, but the output seems to be limited to about 700mVpp.

Distortion pedals use clipping to distort, which means they chop off signal above a certain level, period.
If you choose that level too low, you will lose apparent volume when switching the pedal in; or increase it if set too high.
Classic pedals use a couple diodes antiparallel, which if Silicon clip at around 700mV peak, so that's a very common value.
The FF uses no diodes, but saturates a gain stage; so at the collector of the second transistor you'd get from 9V to saturated transistor plus what drops across its emitter resistor, probably around 7 or 8Vpp.
Nice distortion but it will *destroy* the guitar amp preamp input, so it *has* to be padded down.
The designer does that by using a voltage divider: 8k2 (main load) in series with 330 or 470 ohms across which is developed the output signal.
If you want more, leave everything as-is but rise its value; 1k will probably be all you need, 2k2 tops.
Don't overdo it because you will lose control; the higher it is (the extreme would be tapping output signal straight from the 2nd collector) , the less the FF distortion will matter because the next stage will, which is unpredictable, each amp will behave differently, you don't want that.

Previously I was using a tele with single coil pickups that max out at about 300mVpp, so using the fuzz face was great - it provided the dirt and a volume boost.

Recently I switched to a guitar with humbuckers that output about 800mVpp and the FF still outputs a signal maxing out at 700mVpp, just now with more clipping. It's like it hits a brickwall at that amplitude.

Is this just a reality of the FF circuit or is there something wrong?

See above.

FWIW, when I engage the FF - the guitar input signal gets bogged down considerably to like 80mVpp.

Yes, the FF circuit is horrible , its only claim to fame is that it was used by Jimi ... who had nothing else available at the time .... and its extremely low input impedance (more so when using cheesy germanium transistors) bogs guitar pickups which can't drive it.

But .... but .... Jimi had killer sound ... what am I missing?

Jimi used Marshall tube amps, turned up balls to the wall, and they provided the killer distortion, period.

Every knob on 10, not even 9.5 or so.

In that context, the FF basically provided boost (to weak single coils) and extra gain.

As cheesy as that gain was, it was gain and made the tube amps distort more.
The non symmetrical clipping added a nice flavour to the mix, the pedal squarewave was buzzy but that was swamped by later tube distortion; while assymetry, once created, remains.

Today many build the FF , plug it into small amps which are not turned full up and are amazed at its buzzy sound.
Oh well.

[waspclothes]

Distortion pedals use clipping to distort, which means they chop off signal above a certain level, period.
If you choose that level too low, you will lose apparent volume when switching the pedal in; or increase it if set too high.
Classic pedals use a couple diodes antiparallel, which if Silicon clip at around 700mV peak, so that's a very common value.
The FF uses no diodes, but saturates a gain stage; so at the collector of the second transistor you'd get from 9V to saturated transistor plus what drops across its emitter resistor, probably around 7 or 8Vpp.
Nice distortion but it will *destroy* the guitar amp preamp input, so it *has* to be padded down.
The designer does that by using a voltage divider: 8k2 (main load) in series with 330 or 470 ohms across which is developed the output signal.
If you want more, leave everything as-is but rise its value; 1k will probably be all you need, 2k2 tops.
Don't overdo it because you will lose control; the higher it is (the extreme would be tapping output signal straight from the 2nd collector) , the less the FF distortion will matter because the next stage will, which is unpredictable, each amp will behave differently, you don't want that.


See above.

Yes, the FF circuit is horrible , its only claim to fame is that it was used by Jimi ... who had nothing else available at the time .... and its extremely low input impedance (more so when using cheesy germanium transistors) bogs guitar pickups which can't drive it.

But .... but .... Jimi had killer sound ... what am I missing?

Jimi used Marshall tube amps, turned up balls to the wall, and they provided the killer distortion, period.

Every knob on 10, not even 9.5 or so.

In that context, the FF basically provided boost (to weak single coils) and extra gain.

As cheesy as that gain was, it was gain and made the tube amps distort more.
The non symmetrical clipping added a nice flavour to the mix, the pedal squarewave was buzzy but that was swamped by later tube distortion; while assymetry, once created, remains.

Today many build the FF , plug it into small amps which are not turned full up and are amazed at its buzzy sound.
Oh well.

Great answer, thanks for taking the time to explain all the reasons why the FF isn't what I want in this situation. I was looking for a boost to get a bit more distortion out of the first preamp stage of my amp, and the FF buzzyness and amplitude drop compared to the humbucker pickups wasn't getting me there. I may modify it for a hotter output signal as you mentioned, but it seems like ultimately I need something that will just BOOST the signal so I can let that first pre-amp tube distort more. I'm already getting all of my distortion from my amp by setting the volume to 10 (deluxe reverb) and using an attenuator, but I was hoping to have a pedal for a "more distortion/sustain" type sound for solos and my homemade FF is the only pedal I have at my disposal.

When you said that a really hot signal (8Vpp) would "destroy" the guitar preamp input, do you mean physically damage? I always wondered if there was a limit to how large of a signal an amp can handle and if actual damage can be caused. Thanks again,

[The Dude]

If you're only looking to boost the input signal and not add a distortion effect, you might try building the LPB-1. It's a very simple circuit and works well. I had one years ago to drive a Marshall Plexi harder and it seemed to get me where I was looking to go. If only I still had that plexi..............

[waspclothes]

If you're only looking to boost the input signal and not add a distortion effect, you might try building the LPB-1. It's a very simple circuit and works well. I had one years ago to drive a Marshall Plexi harder and it seemed to get me where I was looking to go. If only I still had that plexi..............

[ATTACH=CONFIG]33943[/ATTACH]

Thanks Dude, wow that's a simple schematic!

I actually just ordered an Xotic SP, which is their OTA based compressor to try. It can get 14db of gain and be used as a straight boost so I'm hoping that will push the amp a little more. Unfortunately I don't have much time for DIY pedal building in the next few months, but I appreciate the schematic.