Fuzz face fun but annoying problems!

[Filip_Mikuz]

ok so ive built a silicon(108c) fuzz face to the original schematic and it works, well sort of.
-The effect only stars working when i turn the volume on guitar to about 90% before that its just normal guitar.
-If i turn the fuzz to full i will get a screeching noise that also picks up AM radio from bosnia(guitar settings volume: 0% tone: whatever)
-if the fuzz is on full and i turn guitar nobs i can make cool radio noises
-this happens on both battery and PS and yes i did check the schematic and soldering.

Thanks in advance for your help

[Kipper4]

Welcome Filip
Is it in an enclosure?

[GibsonGM]

Post your schematic, my friend    I bet with 1 or 2 parts, we can fix that easy.  AND, what kipper was getting at is - if you put it in a metal enclosure (box...) that is grounded, you will probably find the interference thing disappears.  That is the first thing to do.

Fuzzes normally clean up when you turn the guitar's volume down.    Box it up, dude.

[smallbearelec]

The BC108C is a very high-gain device, and the standard bias resistors may not be right in this case. That's presuming that the wiring is correct. Here's my take on breadboarding a silicon FF:

http://diy.smallbearelec.com/HowTos/BreadboardSiFF/BreadboardSiFF.htm

[Philippe]

Fuzzes normally clean up when you turn the guitar's volume down.

this feature/characteristic is what makes a fuzz pedal versatile. consider installing a pre-gain control to trim the signal going into your fuzz circuit. a fuzz running full bore can pick up all kinds of random signals in the immediate area (radio, CBs etc.).

[Filip_Mikuz]

hi!
heres the schematic

i also added a decoupling cap on 9+.
i measured the bias it was 4.6V which is perfect.
and the resistor is 330 not 470 also the caps are reversed.
i would like to upload a layout but dont know how to.

[Elijah-Baley]

That schematic is PNP germanium version.
Compare your layout with NPN version. Check orientations of caps and transistors.

Sometimes I got working my effects, but I got noises problem or odd behavior in high gain settings or also moving the volume pot of the guitar. it was a ground problem.

[Kipper4]

The caps look the right way round to me for a positive ground circuit (check out the battery orientation)in the schematic.

[Filip_Mikuz]

I know i made a npn the ground is negative. The problem i suspect lies in the feedback section. Because  it fuzzes at 90% and also picks up am radio

[GibsonGM]

That doesn't say much, Filip - if it's not in an enclosure, that may well be what is making it pick up RF interference. Any circuit with runs of wire that has gain is susceptible to this (the more gain, the more loops of wire, the worse it may be).      Fuzzing at 90% may be perfectly normal.   I have made FF's that do just the same thing, and are great when in an enclosure...at low volume settings they are more of a BJT boost.
If it's the fuzz sweep that bothers you, it is possible to taper the potentiometer to spread the fuzz out more...

If you're worried about the feedback section, then just look at the 100K from emitter2 to base1, see if it is there, all done!  What makes you think it's the feedback section?  Every symptom screams RF interference and a pot with wrong value/and or taper...if it is built like that schematic, it WILL work, those are the laws of physics... 

[Filip_Mikuz]

I will be drilling the box on thursday or on monday when i can go to the schools workshop, so will see then.
in the mean while you can check out the board

i managed to upload it.

thanks for all the help.
if theres still a problem you will hear about it in a few days!

[GibsonGM]

If it is on a breadboard, you CAN try shielding it with a piece of aluminum foil that does NOT touch any components, but is connected to ground by a jumper.  Not perfect, but it might show a reduction in interference, which would prove where it's coming from...

[Guitar Poppa]

Hello to everybody

A common way to fix such auto-oscillations is to place ceramic capacitors between collector and base of each transistor.
47pf on Q1, 100pf on Q2 should work fine, reducing the bandwith up to 8 or 10 kHz.
If otherwise nothing is wrong on your card (circuitry, capacitor polarity, etc) these negative feedbacks on each transistor should stabilize the circuit.
Don't forget that in antique FFs, the bandwidth averaged just 5 kHz...

Such add on were common in the seventies in Hifi and HQ public adress gears...
With 10 or 22pf, the bandwith was reduced to 50kHz, and stabilized the preamps...

You also may try to put a 47pf ceramic capacitor between the input and the ground.
But it does not work everytime, and depends too much of the characteritics of the guitar cable.

Good experimentations !
Guitar Poppa

[Filip_Mikuz]

ok so ive made anoter version on a breadborad following the instrustions form the linke someone posted. It works perfectly. so where have i gone wrong?

[lethargytartare]

Well, now with two instances, one that works and one that does not, you can start stepping through each signal and compare the two.  See where they start to diverge in performance (voltage, or with an audio probe, etc.).  You have to assume it's either the components themselves or a build flaw.

Have you compared the voltages on your breadboard build to the voltages on your vero build?

[GibsonGM]

Honestly, you may not find out, Filip!  Yes, do compare the two you have built, as lethargy suggests - you may find a mistake.  But even passing two wires too close to each other may have contributed to your problem - and many breadboards have their own capacitance problems, so the two boards could be different!    So, if nothing shows up, it may be an issue like that.

What Poppa said is very true - often you can stop oscillations and RF problems with feedback (or shunt) capacitors...I would have led you in that direction AFTER you had tried an enclosure, if the problems remained.   I bet it was the breadboard, or long wire runs coupling into parts of the FF that shouldn't be coupled. 

[Filip_Mikuz]

ok ive measured voltages on q1 and q2. i dont have time to verify it, because its getting late.
here are my findings
breadboard q2:
C: 0,6v
B: 1,2v
E: 4,5v

Stripboard q2:
C: 4,5v
B: 1,2v
E: 0,6v

what the hell. ill check it again tommorow

thanks for the help, ill try the cap as soon i a get it

[GibsonGM]

On the breadboard - do you have the transistor pinout backwards? 

You may find the voltages match, it only tells you the transistor is set up correctly.  If you find the same voltages, just write it off as a quirk!   

These problems usually have much more to do with shielding than an assembly malfunction...poor solder connections, too, so you could look at them with a magnifying glass...

[Filip_Mikuz]

OK so i tried my smallest capacitor that i have in stock 2.2uF and it worked. i ran it on the C and B of both Q1 and Q2 and it worked in both cases 
only thing is that the tone became a little bit darker. 

i dont care as much on friday i have some time and i will try the pF hopefully keeping the tone the same.
im now ready to install it in the case 

Thanks again for all the help

P.S. does anyone recommend any schematic for a 9v filter and regulator, because i can still hear that 9v ripple

[GibsonGM]

Personally I'd install it without the cap, but if you're happy with the tone, by all means include it for some security. pF values shouldn't drop enough HF for you to hear the difference anyway. 

If you run it on a battery there should be no 9V ripple, at ALL, since there IS no ripple present with a battery.  If it's your PS, you should look into either buying one that's regulated (my preference...), or find one that outputs at least 12V at 100 or 200mA.  Then run that into an LM7809 regulator chip (schematic for how to do this on the 7809 datasheet, search internet).   You'd box that up and use it to distribute power to all your pedals (many good schematics for doing this are readily available, no need to reinvent the wheel).  You need a few volts over your desired voltage to run the regulator...

Simpler to buy one that has a daisy chain for multiple pedals...no need to put a regulator into each pedal you build.  Can be had for like $20 US.