Fuzz Face troubleshoot

[smallbearelec]

What do you mean by biasing? how can I do this and what is it for?

The voltage at the Collector of Q2 should be 4.5 +/- a little bit using the resistor values that were shown on the slip that came with your transistors. Substitute a 10K or 25K pot for the 8.2K resistor and you can adjust this voltage. The setting you choose will change the "squishiness" of the effect.

BTW: Experimenting with mods is best done on a breadboard. Now that you have been through the hard part of making a soldered build to work, back up and learn how to use this tool:

https://www.smallbearelec.com/HowTos/Breadboarding/BreadboardIntro.htm
https://www.smallbearelec.com/HowTos/BreadboardSiFF/BreadboardSiFF.htm

Enjoy your new effect!
SD

[rtrags]

How common is it to solder the circuit together with the trim pot, so you can go back and tweak it later? I kinda like the "squishyness" but having that be adjustable seems like you can have multiple pedals in one.

[rtrags]

And one last question, is it common for the fuzz to really go nuts as my guitar's volume heads from 9 to 10? It seems like a smooth transition from 0-9 but that last 10% turn really kicks it up.

[LucifersTrip]

How common is it to solder the circuit together with the trim pot, so you can go back and tweak it later? I kinda like the "squishyness" but having that be adjustable seems like you can have multiple pedals in one.

very common, especially for germanium which will change with temperature. also, very common to have a "real" external pot there instead of the trim inside

And one last question, is it common for the fuzz to really go nuts as my guitar's volume heads from 9 to 10? It seems like a smooth transition from 0-9 but that last 10% turn really kicks it up.

yes, that last bit is where it kicks in to full. if you want to slow down the end part of the sweep a bit and spread it out, you can try a reverse log pot
http://www.dirk-hendrik.com/temp/pottaper.gif

[rtrags]

Ok i used a trim pot, solder everything together and it all seems to work fine except when the volume and fuzz knobs are turned all the way up, the pedal puts out a really loud really high frequency tone. the only change I made was i put the 22uF cap directly across the lugs of the fuzz pot instead of on the circuit board. I grounded everything in a line (no star ground, essentially a broken ground loop). Any idea what could be causing this really shrill tone?

I have read something online about germanium transistor with high frequency feedback when they get hot but the circuit worked fine when it was on the breadboard.

[LucifersTrip]

...and guess what the #1 way to compare to your earlier version that worked would be?  yep, voltages again.

once you have a circuit working how you want, it's a great idea to get the voltages. That way, you can troubleshoot if it ever fails, you can duplicate it easier if you build it again and you can help others who are currently or are planning building it.

anyway, take the voltages now and see how close they are to the ones I posted earlier.

also, if you haven't already, try powering with battery instead of adapter

...and you might be able to tame it with a 100-200pf cap across BC of either Q, but might lose some fuzz

[rtrags]

Voltages of the soldered circuit are the same as the breadboarded version. The voltage on Q2's collector varies from -8.23 to -3.81 as i sweep the 10k trim pot (in place of the 11k). Could this high frequency tone be coming from the transistors if i damaged them while soldering? Even though I did use a heat sink, and the voltages are consistent before and after. It only generates the noise when both volume and fuzz are cranked up between 90-100%. All my solders are good. I am using a battery that gives me 8.56V.

What would that 100pF capacitor do? Also, this may be unrelated but when put my cry baby infront of the fuzz and run them into my amp, there are almost no bass frequencies, the wah seems fairly unresponsive, though it works fine independently.

I really appreciate the on going help too

[LucifersTrip]

Voltages of the soldered circuit are the same as the breadboarded version. The voltage on Q2's collector varies from -8.23 to -3.81 as i sweep the 10k trim pot (in place of the 11k). Could this high frequency tone be coming from the transistors if i damaged them while soldering?

maybe one of the masters can give you a better answer, but my guess is no. if the transistor was damaged, I wouldn't expect (1) the same voltages as before and (2) I wouldn't expect it to sound good thru the first 90%. I'd expect bad throughout.

What would that 100pF capacitor do?

tames the fuzz a bit...removes high end, sizzle or fizz...usually used in silicon versions since they are harsher.

Also, this may be unrelated but when put my cry baby infront of the fuzz and run them into my amp, there are almost no bass frequencies, the wah seems fairly unresponsive, though it works fine independently.

place the wah after the fuzz

[pinkjimiphoton]

by biasing they mean setting the operating range of the second transistor. what ya wanna do is swap out the 8.2k resistor for a 10-20k trimmer pot.

the conventional wisdom is to bias to about 1/2 b+ going to c of q2 or roughly 4.5 volts.

my advice as a fuzzface-aholic is to crank the fuzz and volume full, then adjust the trimmer til you get the best sweep on your guitar from off to full blast. if it glitches during the sweep, adjust it a little hotter until you find your personal "sweet spot" where it interacts most with your guitar.

then the volume and tone knobs of the guitar will effectively be matched to the rest of the circuit, and you can get a crazy lot of sounds out of the thing, from crystally clear compressed to over the top noise.

one caveat...if building it as a positive ground, make SURE it's on it's own power supply, not daisy chained with other pedals. as you noticed, the ground is reversed, and it will short out your power supply. use it's own wart or put it on a battery.... or use a charge pump to convert the incoming power to the negative power required by the pedal.

personally i think faces sound best with a battery, and nearly dead one, at that!!

good luck mate!

[pinkjimiphoton]

And one last question, is it common for the fuzz to really go nuts as my guitar's volume heads from 9 to 10? It seems like a smooth transition from 0-9 but that last 10% turn really kicks it up.

that's a sure sign of improper bias.  you *CAN* exploit that to get more ragged fuzz...if you want it fuzzy no matter what and don't use your guitar knobs, you can turn the voltage down a little more and get more fuzz, and make your volume control almost a switch.

or, turn up the voltage slightly to hit the sweet spot. if it's right, particularly if it's a silicon or hybrid, you should get no glitch at all, should smoothly transition from all the way off to full blast.

NOTE...this will make the face slightly LESS fuzzy, but will make it interact much better with the guitars and amps. i have mine like that (a hybrid pnp with ge and si transistors at the moment, i use different transistors in the summer and wintertime cuz where i live the climate changes so much) and can literally turn the face on at the beginning of the nite,
and play all nite long with just the one box. there are myriad tones in there beyond just fuzz.

[rtrags]

I set up my oscilloscope and the noise is clearly evident when the volume and fuzz are cranked. But the noise seems do decrease as i increase the resistance of the 10k trim pot (on Q2's collector), but not to an acceptable level. I traced the noise back from the output jack, to the volume pot, then to the 0.01uF capacitor. Here are some images of the circuit output.

This is the output with volume and fuzz full up, and the trimpot set to 9.8k http://www.flickr.com/photos/84722452@N06/7774285254/in/photostream

With the fuzz turned back to about 85%, regular acceptable noise, http://www.flickr.com/photos/84722452@N06/7774285426/in/photostream/

And this is the signal going into the 0.01uF cap. Its just the dc signal with some square noise (this square noise has the same period as the noise in the first picture) http://www.flickr.com/photos/84722452@N06/7774285710/in/photostream/

That 0.01uF cap I am using is a 500V cap, although I have read that there is no harm in having the rating way in excess of the pedal's running voltage.

I am going to switch out the trim pot for an 11k (small bear's recommended value for that position with my transistors). Hopefully this slightly higher value will drop that noise but the 10k pot worked fine on the breadboard.

[pinkjimiphoton]

YMMV, but IMHO screw the o-scope, use your ears. alot of the noise you'll see on the scope won't matter in use, and you probably won't need to dime the pedal ever.
what i describe previously is to get the guitar interfaced properly to the circuit...the guitar must become PART of the circuit, in fact...
when the bias is right, with the ff pegged, you'll get a smooth sweep with the volume control.
once that's right, the fuzz and volume become properly interactive with the guitar controls.
you can either back off the fuzz level slightly (which will nuke most of the noise) or if you need it pegged, add a couple snubber caps to the circuit to short the high end fizzies and noise to ground like lu suggested.

but using an oscope to bias a fuzz face is shooting ya in the foot...the "noise" is part of the sound. my advice is don't worry about it, use your ears.

edit: looked at the pics....again... use your ears, not the scope.. and remember, what i suggested is to set up the face to get it interfaced right with the guitar...
you don't need to run the knobs on the face pegged in use. only when setting the bias...that will give you the max dynamic range and headroom should you need it.

one of the best things about a face is playing clean rhythm on it with the guitar way down...hendrix city.

peace mate.

[LucifersTrip]

I am going to switch out the trim pot for an 11k (small bear's recommended value for that position with my transistors). Hopefully this slightly higher value will drop that noise but the 10k pot worked fine on the breadboard.

after all the previous bias talk, you haven't mentioned what your Q voltages are and whether they are close to "normal". ie, what're the voltages at 10K, etc...

another thing not mentioned yet is that many adjust the 33K instead or in addition to the 8.2K to adjust the bias. try various combos....