Fuzz Face tweaks

[tjk3052]

I built my first pedal, a GGG fuzz face with the "late 60's botique" mods a while ago, (schematic). I like some of the sounds I get out of it, but a lot of the settings are kind of flabby, torn speaker sounding. I replaced the Si transistors with Ge ones (PNP) from SmallBear and it definitely sounds better, but how can I get this thing sounding smoother and less fart-like, lol.

[Stevil]

GEOFEX has an article called Technology of the Fuzz Face that will explain the entire circuit, piece by piece, including mods for different things. It's a very informative read for someone getting into this.

[11 Gauge]

The Fuzz Face circuit is so simple that it's EASY to tweak.

Most of the time, the farty, flabbiness can be cured by making the input cap (in your case, C1) smaller, sometimes much smaller (stock value is 2.2uF).

Either get a rotary switch, or temporarily put a pair of jumper wires in the input cap's place. Now sub in progressively smaller input caps. Don't be surprised if your final cap size is much smaller, like .22uF or even .1uF.

I noticed that on the Boutique FF clone that the output cap (C3) is also a little larger than a stock unit (.1uF). If you want to tighten things up further, reduce this cap as well. You can repeat the above input cap method, or try .047uF as a pretty good and standard value that works well in most cases. But some folks go smaller than that, all the way down to the stock value of .01uF.

Some folks will also reduce R3 (100K) to tighten things up. 47K is not uncommon, but you might opt for a 100K trimpot instead, and tweak it to taste. If you ever go back to silicon transistors, bypassing R3 with a small cap (220pF to .001uF) will typically both tighten and smooth out the tones even further.

And another trick to tame silicon trannies a bit (if you ever go back to them) is by bypassing the collectors (NPN silicon) with a small cap as well - 470pF will really smooth things out (and reduce or eliminate oscillations), but you can go smaller for a more subtle effect. Keep those silicon units handy - you can both tighten up the pedal AND make it smoother, which is actually trickier with the low gain and sometimes leaky germanium units, which will always pooch out much sooner than silicon.

One final thing to try would be to reduce C2 (22uF), to limit the amount of bass that the transistors are "shelved" at. I've seen folks go as small as 1uF, but that's probably a bit drastic. 4.7uF - 10uF is typically sufficient IMO, but once again you can jumper or rotary this cap to "hot swap" values until it's tweaked to your liking.

So there you have it - SUPER simple circuit, many options to tweak to get it to behave to your liking. Enjoy!

[tjk3052]

Can't believe I hadn't found that geofx site before, thanks.

11 gauge, I was hoping you'd respond. Your 2 cents are always more like 20 bucks, lol. Looks like its time to break out the iron again. I REALLY wish I would have paid attention when I had to take an EE class in college.

[cousinpaul]

The 8.2K resistor on mine has been replaced with a 20K pot for bias adjustment. The sweet spot seems to be around -4.5 V DC.

[11 Gauge]

Originally Posted by tjk3052

Your 2 cents are always more like 20 bucks, lol.

Just pay the 10X markup forward, if you don't mind.

I don't think that EE will get you very far with tweaking a stone age circuit like a Fuzz Face - the circuit design does things that would either make an EE scratch their heads, or cringe. They would probably turn it into a class A buffer with .00001% THD.

[tjk3052]

Originally Posted by 11 Gauge

They would probably turn it into a class A buffer with .00001% THD.

Touche

[tjk3052]

I replaced C1 and C3, one at a time, with .22 uF and .022 uF. Its brighter now, but upping the gain still produces a lot of flab. It sounds like one of my other drive pedals when the battery is dying (but its not). I don't think its a bass issue because I put a Barber LTD SR in front of it and maxed out the tone knob on it, which cuts the bass by a lot, and it still had that problem (not sure if that makes sense). I'm going to try adding a 10 to 100pF from the collector to the base on the second transistor as mentioned on the Geofex site and see if that helps.

For such a simple circuit it can still be a PITA.

[11 Gauge]

Originally Posted by tjk3052

I don't think its a bass issue because I put a Barber LTD SR in front of it and maxed out the tone knob on it, which cuts the bass by a lot, and it still had that problem (not sure if that makes sense).

This is a no-no unless you really tweak the input of a Fuzz Face. It has to be the first pedal in line, or you typically get a nasty interaction from the "temporary buffering" effect of the previous effect.

There are a few more things you can try, assuming you haven't done so already. Do you have a 10K trimmer for R5? If not, consider adding one. Better yet, you can use a 10K pot and adjust it externally, to compensate for bias changes in germanium transistors as the temperature changes, just like Analogman's "sun dial."

...And second would be to add the 50K pot on the input like the '69 pedal uses. This attenuates the signal so that it isn't overshooting the max voltage that those poor little low gain germaniums can pump out.

But I have to be honest - the two above ideas will only (typically) get you so far with germanium. Their gain is so low that it's easy to exceed what they can reproduce without farting out. You may want to consider going back to silicons and "softening" them with the many options that you will find at Runoffgroove, Geo, and about 3,000 other sites.

...Yet another option would be to modify the pedal into Joe Gagan's Easy Face. He addresses the "flab" by doing the following:

- 250K input pot to really cut the amount of signal that hits the pedal. The 50K used in the '69 may not be sufficient.

- 2N3906 silicon PNP resistor for the first slot ONLY. It tightens things up, handles a bit more gain, and isn't as responsible for the germanium qualities as Q2 is. You leave Q2 with the germanium unit that's currently in the pedal.

- 100K input cap blend pot, which allows you to fine tune between .01uF and 3.3uF (2.2uF is usually sufficient) - this will help you to gauge exactly how much bass the pedal can handle, on the fly. It also allows you to "tune" the FF for different guitars.

The side benefit of the Easy Face tweaks are that it uses really common stuff except for Q2. This makes it "easy" to build one (and cheaper). And there's a LOT more flexibility than a germanium-specific FF with most components hardwired will ever offer. This makes it "easy" to live with, since it's one of the few FF variants that will adapt to most rigs.

...But perhaps the ultimate solution is to buffer the input to really raise the input impedance, so that Q1 isn't overtaxed with the whopping signal that it must reproduce (in some distorting fashion). But this makes a simple circuit a bit more complex, typically adds another transistor (Q1A?) that will need to be a PNP unit, will require it's own biasing, what have you. I don't suggest this, but I know that R.G. has some ideas on it, and Subdecay and others have implemented it in their fuzz designs.

...Something else to try would be to put a mu amp in front, to buffer things up and increase the input impedance. But it's typically WAY too much, even with the boost set below unity gain. Replacing the J201's with 2N5457's or even 2N5458's would probably help quite a bit. I would keep this as a last resort, in lieu of what I stated in the very first paragraph!

So there you go - another small novel committed to tweaking the Fuzz Face! You can get better performance out of it, as long as you bear in mind that it's a very crude circuit that requires adding some flexibility and adjustability to do so - something that FF diehards can be strongly against.

[tjk3052]

I like the easy face mods, I think I'll try that next. The "pre-gain" pot would be the same effect as lowering the volume on the guitar, right? I think the blend knob would be a good addition.

When I'm replacing caps, does it matter if I switch from an electrolytic to film caps?

Continued thanks - Tim

[11 Gauge]

Originally Posted by tjk3052

The "pre-gain" pot would be the same effect as lowering the volume on the guitar, right?

When I'm replacing caps, does it matter if I switch from an electrolytic to film caps?

The pre gain is not exactly synonymous with lowering the volume on the guitar. It actually alters the way the signal gets into the pedal, although it will have a bit of a series effect with the Z out of the guitar.

The biggest difference is that the guitar's vol pot bleeds the signal to ground, while the pre gain is simply variable series resistance - it's the equivalent of a grid stopper for a tube amp gain stage.

Switching from e's to films should not matter, as long as the desired capacitance is to spec. That said, everyone seems to have their own "mojo preferences" with component composition. Start with the cheapest stuff and work your way up from there, is my best advice.

[tjk3052]

Just to put an ending on this thread...

The biggest problem was that R5, even with a 10k trim pot, needed to be higher. It took another 10k resistor with the pot to get it to purr. I saw one Roger Mayer mod that had that resistance at 18k, which is about what I end up with. Surprisingly, Si transistors act about the same.

The reduced input and output caps definitely tightens things up and still leaves it with plenty of bass. The "bias" pot goes from more transparency to more saturation and sustain. It might be interesting to increase its value to get more shades of OD. The tone knob doesn't do much except act as another gain control. I might get rid of it and add the blend control of an easy face. Also, I might add a small cap from collector to base on the second transistor to see if that makes it smoother.

But now I finally have a fuzz that sounds great at most any setting

Thanks

[11 Gauge]

Originally Posted by tjk3052

JSurprisingly, Si transistors act about the same.

It's really hard to get this across - I'm glad you found out about it. There's good reason that Analogman, Fulltone, and others offer a silicon fuzz face. The biggest obstacle is finding a silicon equivalent that has the same low Hfe as a germanium unit. Once you do that, you're basically "in." And even if you don't, you can "saddle" higher gain silicons with the variable input, bleeder caps, and bias tweaking (as you also found out).

If you really want to get it as smooth as possible (and get it into OD territory as you mentioned), BY ALL MEANS check out the Sili Face II over at runoffgroove.com because it's a very friendly and well thought out FF variant. Excellent sounding pedal that you can build on perfboard in less than an hour! I should have mentioned it earlier, but I really thought that you were trying to stick more to the original recipe and just nuke the flub.

[Noodler]

Thanks for the links 0.11. I'm about to breadboard one to start with. The first Sili fuzz at runoff.com sounded best to me, so I might go for that one. I love how it had sound clips too. What a great site!

[Montana_Dawg]

Originally Posted by 11 Gauge

Just pay the 10X markup forward, if you don't mind.

I don't think that EE will get you very far with tweaking a stone age circuit like a Fuzz Face - the circuit design does things that would either make an EE scratch their heads, or cringe. They would probably turn it into a class A buffer with .00001% THD.

LOL.....which is why the audio engineers absolutely LOATHE the venerable JRC4558!

[limbe]

Yes,you can change capacitors,resistors,transinstors and so on BUT in the end you will end up with a(hopefully) optimized Fuzz Face.I`m not trying to put anybody down who wants to have a Fuzz Face in their arsenal of distortion/overdrive pedals.(Me I`ve still have a Sola Sound Tonebender in the closet somewhere)but if you take a look at the guitarists who are still around and used the Fuzz Face or Tonebender in the sixties they have generally moved on to newer pedals.W.B.R Limbe

[russpurdy]

i just thought i'd throw this out there if the OP is still checking this thread. I built a silicon fuzz face with the 70's mod from GGG and I had problems with it sounding fizzy and farty as well. I never really liked the thing until i tried turning up the volume knob on it. For some reason, cranking the volume seemed to smooth things out and now the thing absolutely roars. It's my favourite pedal now. Try cranking the volume knob on the actual pedal and you might get what your after. I know you'll get a bit of a volume boost when you engage the fuzz but it works for me. I always want the fuzz to come in and destroy everything, not just distort at the same volume! Good luck to you!