Fuzz face sound disappears at last 10%

[Filip_Mikuz]

hi!

ive built a fuzz face and it works fine until you turn up the fuzz. the sound gradually gets thicker at 50-70% and then thinner till it completely disappears at 90% and i just get short bursts of sound. its not a major deal as it is, but on stage it can be deadly(if any accidents happen).


ive combined the top schematic with the bottom one. i ve added a 100uf and diode(mine is 4001) and i added that cap (mine is 220pf) between the collectors.
note: the sound cut out before i added the other stuff.

help me out please!

[mth5044]

Sounds like your fuzz pot is wired incorrectly. Make sure the cap is the only thing on lug 2 and lugs 1/3 are connected properly.

[GibsonGM]

Sounds like your fuzz pot is wired incorrectly. Make sure the cap is the only thing on lug 2 and lugs 1/3 are connected properly.

This, or a problem with the pot?  Wiper intermittent kind of thing? 
Quick spray with some pot cleaner could rule this out and is also beneficial...

[Filip_Mikuz]

ive tested the pot out with a multimeter and its giving me a clear signal. i also attached a cap just on 1 and 2 and the result is the same.

[mth5044]

Check for solder bridges around the pot. You said you attached the cap on just 1 and 2, which is a little confusing. Is it on both of them? It should only be on lug 2. Do you have an image of your layout?

[ashcat_lt]

Check for solder bridges around the pot. You said you attached the cap on just 1 and 2, which is a little confusing. Is it on both of them? It should only be on lug 2. Do you have an image of your layout?

Both the bottom of the cap and lug 1 of the pot connect to ground.  Doesn't matter how you get them there, they ARE connected.

[Filip_Mikuz]

yeah sorry i was a fool. i did connect a cap on 1 and 2, but what i ment was 2 and ground seperating it from where other things are grounded.

BUT an interesting thing happend when i wired it correctly. the sound came at the 90% and up but when the guitar is idle it squeaks like crazy.

[Filip_Mikuz]

the squeak is actually a tone, the likes of witch a computer would make and is affected by guitar volume.
FUZZ:
vol 100
fuzz 100

Guitar
vol 90 and up (low pitch)
vol 90 and down (high pitch to no tone)

[Ben Lyman]

EDIT: You guys are too quick for me 

You can solder the cap right to the pot across the wiper and ground lugs AS LONG AS the ground lug is GROUNDED. Check to make sure all ground lines are connected including that pesky gain pot, it might not be.

Did you use a 10k trim pot to set the bias or just use the 8k2 fixed resistor? I've had some FF gain pots do similar things when the bias was off. Also, when the tranny gains were too low but I'm sure your Si gains are probably high enough.

Combined two circuits? Hmmm... I'm not sure about that...

I highly recommend measuring the tranny gains and plugging the numbers into Joe Davisson's Fuzz Face calculator... it's foolproof and provides instant satisfaction! 

[Filip_Mikuz]

i used a 10k trim and ive set it for 4.5v. it must have something to do with the RF oscillation, because FFs pick it up at 90%. thats my guess.

[Gus]

First check the stickyhttp://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Silicon FF circuits need a good layout.  They can take off when the gain is around max
Short wires,
Signals should cross at 90 degrees if you can't keep them far apart.
Good power supply filtering

A picture might help

4.5VDC is a web myth, people need to ignore that "web rule".

measure the collector voltages when the gain control is at a minimum and again when the signal cuts out.

A little off topic I tried a inexpensive 100uf electro as a power filter in a recent Silicon FF like build it turned out not to work correctly I had low frequency motor boating that when away with changing the cap to a better one.
What brand cap, something from china?

You can add a fixed resistor in the wiper to cap to limit the max gain. This is not a real fix

[Filip_Mikuz]

Q1:
C 1,2v
B 0,57v
E 0
Q2:
C 4,5v
B 1,2v
E 0,6v

values are the same no matter if its maxed or idle(fuzz)
the transistors are both BC108

update: it only squeels when the guitar vol is above 90%
up tu the 90% it buzzes

[Ben Lyman]

I see those two schematics have different input caps.
Did you use the .22uF input cap or the 2.2uF?
I don't really know if it makes a difference but I would stick with the traditional 2.2uF for a FF.
It might help with your guitar's interaction with the circuit, I dunno.

[Filip_Mikuz]

it the standard 2.2

[Ben Lyman]

Sounds like you did everything right. Maybe your guitar cable is acting like an antenna, you can try a small resistor in series right before the input cap, that is sort of what the "Smooth" pot would be doing (I think)
I've done this with some noisy FF's, I think I used a 100ohm resistor but maybe it was a little bigger than that. You'd think you wouldn't want to reduce your guitar's output into the fuzz pedal but some of my FF's had so much gain that it made no difference in the long run.

[Filip_Mikuz]

ok ive tried a 100ohm and it did nothing. ive tried a 100k and it removed the squeal, but there was a lot of hissing.

[Ben Lyman]

Hmm.. that's a lot of resistor... Remember what Gus said, 4.5v is a myth.... I always turn the gain up all the way and adjust by ear, volts be damned!

[PRR]

Cut-out at maximum gain suggests a layout problem. Output sneaks back to input and makes a squeal, often ultrasonic, which knocks-out the audio, sometimes with off/on action. Yes, the guitar impedance is part of the oscillations.

Short. Neat. Segregated.

[Filip_Mikuz]

a 100k on the 9V+ right before the coupling cap (100uf) seems to remove the squeal, but also makes every thing more bassy
(also now i can hear radio very clearly)

any suggestions?

update: i found out that a 220 does the right job, but it still squeaks a little on a PS.
it works a kind of treble boost. when guitar is idle it squeals, but when you play it the squeal occasionaly kicks-in in a form of a treble booster

update2: it is still oscillating just at a lower freq. the squeal has just turned into a buzz. its similar to 60hz, but the question is where? im running it on a battery

[midwayfair]

Still sounds like positive oscillation to me. I bet it changes pitch when you play with the tone knob. Your input and output are connected somehow -- even if it's through the air. I'm also going to suggest that it's a layout issue. Would you post the layout and photos of your build so that can be ruled out? Otherwise everyone's going to keep telling you the same guess. Adding resistors and such to the input and output is working around the issue without solving it.