god this silicon fuzz face is driving me insane! even after hours of research!

[ode2no1]

i cannot keep it from oscillating. well, i can, but it just doesn't sound right. i tried a 68pF cap between collector and base of Q1 but i still got this crackly decay when rolling down the guitar volume. then i tried adding two small resistors between the emitters and ground but then it doesn't sound very fuzz face like at all. not enough gain. i already have a germanium version that i built up a few years ago but i really wanted to have both versions. the only way i could get it to sound halfway decent is by going hybrid with a germanium NPN, but compared to my germanium FF it sounded muddy and lackluster all around with a bit less midrange and volume...and still a bit of crackling. what else can i try? i ended up socketing everything but the .01uF cap. even with some very low gain silicons (typ.40hfe) i get the nasty crackling and high frequency sort of modulation on the decay of notes. it's so frustrating to have built up a blue magic and IC big muff recently but this low parts count ultra simple circuit just won't work correctly. i'd really appreciate a push in the right direction.

[petemoore]

  It's doing what it does.
  Whether it's working would be the first question.
  Without knowing what circuit you're building it's difficult to determine anything.
  The debugging sticky tells how to take voltage measurements, that and a schematic are a good start for helping us answer questions.
  A Fuzzface can easily tend to oscillate.

[ode2no1]

ok ok sorry about that. here are the voltage measurements. the battery measured at 8.71v.

Q1 - BC108C
E=0.0v
B=0.57v
C=1.07v

Q2 - BC109
E=0.63v
B=1.05v
C=4.39v

i've checked solder joints and everything looks fine. i did add a power jack but have just been powering it by battery. it sounds good underneath all the oscillation but when i try the small cap trick it loses all of that bright fuzz face character and doesn't clean up nearly as well as without the cap. thanks a lot. i hope you guys can lead me in the right direction.

and this is the schematic follwed by the vero layout i used:

[jacobyjd]

I've run into the same issue with that layout, specifically--try putting a 100pf (I think) cap from the input to ground along with the 68pf cap you already had. That's done it for me before.

[sean k]

Don't you need at least .6V sitting on q1's base for it to open? maybe the attack on the notes is keeping it open then on decay it's shutting off so you could either bias it in someway, 1M from 9V to base and 56-100k to ground or lower the resistance of the emitter to base feedback resistor so more of the voltage on the emitter of Q2 gets through or lower the collector resistor of Q1 though I suppose it's because germs are leakier that self biasing occurs. Maybe a 1M -470k between the collector and base of Q1? whatever gets you +.6 volts on the base of Q1.

[Focalized]

Did you try any other transistors? They're not "mojo" but 2N3904 are very, consistently good sounding. 

[ode2no1]

ok for some reason i csn't seem to get anything above .59v. i kept lowering the the 100k resistor all the way as far as 4.7k, but i still only got .59v. i tried 1M from 9v to base with a 100k to ground and i still can't cross the threshold of .6v. what the heck is wrong with this thing? and i did try 2n2222's as well as these ultra low gain silicons but it's the same thing.

[ode2no1]

i definitely get some slight gating on the decay of notes which means yea...i'm sure i need to get that voltage up on Q1's base but anything i try that gets it past .6 is throwing the bias way way off. instead of around 4.5v it jumps up to 8 or so and the trim i used for the 8.2k resistor does nothing. man i can't believe what a pain this is. i really would rather scrap the whole thing than do the small capacitor trick because it just kills the tone of the pedal.

[mac]

First, I removed those small pF caps from base to collector in my Si ff because they crackle when rolling back the guitar vol pot.
The oscillation could be the use of high gain Si. Most put a small resistor, 100 ohm or so, at q1 emiter to reduce the gain.
Also try a big electro cap + 0.1uf ceramic cap across the battery.

mac

[sean k]

5.9v is close enough and is most probably the diode drop accross base to emitter so thats open. The 100k feedback resistor could be lower in value to put more negative feedback on the base which might cool things down.

[Mugshot]

must be the trannies? try 2N3904 for medium gain.

just hoping it does some miracle, but mojo sent. good luck!

[solderman]

ok ok sorry about that. here are the voltage measurements. the battery measured at 8.71v.

Q1 - BC108C
E=0.0v
B=0.57v
C=1.07v

Q2 - BC109
E=0.63v
B=1.05v
C=4.39v

i've checked solder joints and everything looks fine. i did add a power jack but have just been powering it by battery. it sounds good underneath all the oscillation but when i try the small cap trick it loses all of that bright fuzz face character and doesn't clean up nearly as well as without the cap. thanks a lot. i hope you guys can lead me in the right direction.

and this is the schematic follwed by the vero layout i used:

Hi
I can see that you used BC108 and BC 109. IMO the are faaaar to high in Hfe. I just finished this one but used 2N2222A. The only supst I made was 150pF and 47nF instead of 33. and 1.8K instead of 1.2
The trimput set to 4.7V on the collector of Q2. 15 uF is important for the sound I wanted. I was after the original sound of a Fuzz as I see it, that is the "wholly farty" sound. If you want the more "itchy screamy" 2N3904 might be a better choice. also alter the 1.2K/33uF and the 15uF junction.

You can find a sound sample here.
http://www.diystompboxes.com/smfforum/index.php?topic=76047.msg620484#msg620484
//Solderman


EDIT
BIG opps was a bit fast in spotting the schem. I have used this and IMO its is THE schem for silicon Fuzz faces type of sircuts. Hatts off for
Mr Axis or who ever did this.

[aron]

Anders,

Is the Axis Face really good? I've been wanting to make an Si Fuzz Face for a while.

[ode2no1]

seriously nothing is working. this is killing me cause it's such a simple circuit. i tried 2n3094's, 2n222's, and some very low gain (around 30) silicons but nothing works. the only thing that did it was using a germanium npn for Q2, but i really want a silicon fuzz face. can someone verify that the layout is correct? it looks fine to me but i'm sure i'm not really qualified to say so for sure. i tried disconnecting the whole led/power jack assembly to see if that would help but it's the same story. even at .59v on the base of Q1 it's slightly gating and oscillating. turning the gain down kills the noise but it's still gating. i'm gonna try once more with the 100ohm resistor and then i'm ripping it apart.

[rousejeremy]

Have you tried the smaller Silicon Fuzz vero in Dragonflys layout gallery? http://www.aronnelson.com/gallery/main.php/v/DRAGONFLY-LAYOUTS_0/album18/album144/SILICON_FF_VERO_SMALLER_001.gif.html

I built one last month and it works/sounds great.

[slacker]

What I did on my silicon fuzzface using BC109s was put a 470p cap from the base of Q1 to ground, that was mostly to get rid of radio interference and stop it howling when the guitars volume or tone pots were turned down. Then I stuck a 1n cap from the collector of Q2 to the positive supply, that stopped it oscillating without affecting the sound too much.

[The French connection]

Hi
EDIT
BIG opps was a bit fast in spotting the schem. I have used this and IMO its is THE schem for silicon Fuzz faces type of sircuts. Hatts off for
Mr Axis or who ever did this.

Phillip Bryant, Fuzz central (http://fuzzcentral.ssguitar.com/axisface.php)

Here's a vero:
http://www.aronnelson.com/gallery/main.php/v/French+connection/Vero+Layout/Axis_face_vero.jpg.html

[MattXIV]

I think Q2's base needs to be higher off its emitter - it's only .42V higher in the readings, which isn't enough to produce a base current in a Si transistor.  Ge's Vbe is only ~.3V, which may explain why it sounds ok with a Ge but doesn't with a Si.  I'd try reducing the value of R2.

[ode2no1]

ok so i just scrapped the pedal and built up the dragonfly smaller version and it only oscillates with the fuzz and volume up on full, whereas before it was if the fuzz was up all the way no matter where the volume was set. if i set the volume at 3 o'clock it's totally fine and sounds pretty great thru my little champ 12. the cleanup tone with the guitar volume down is sweet. now like i said, it only oscillates with the volume past 3 o'clock, which i'm willing to live with, but what can i do NOW that the nightmare seems to be coming to an end to fix this?

battery is now 8.58v

Q1
E - 0.0v
B - .56v
C - 1.21v

Q2
E - .64v
B - .89v
C - 4.43

[solderman]

Anders,

Is the Axis Face really good? I've been wanting to make an Si Fuzz Face for a while.

As allways its up to ones individual ear. But I think so and if you are looking after the original sound of a Fuzz as I see it, that is the "wholly farty" sound it's very good to my ears.

Try my crappy sound sample above