Buzzing Fuzz

[andrea2127]

Hello to everyone, i've just build my first fuzz face, an NPN clone with 2n2222 hfe=180 Q1 and a BC 108B hfe=400 as Q2.
The pedal works well and sound good, but when i turn the fuzz pot all the way up, it's start screaming and buzzing in a wired ugly way.

https://vocaroo.com/i/s1epDsyCdlUq

at this link there is an audio sample of the problem.
What could be the problem? Fuzz pot's fault? A cold welding? transistors with too much gain?
Any advice? thank you for the answers!

[GibsonGM]

Can you post the schematic you worked from?

Is the circuit board not inside a metal enclosure?  If so, it can pick up any RF interference in the area, such as from transformers, lights, your amp....radio stations.   So it is not unexpected to have noise when out of the enclosure.

As for 'screaming', if you have wires run too close to each other, and input/output wires too close to each other, you will get coupling, which can result in an amplified signal feeding back into an input, where it is re-amplified, over and over, causing the noise.    Try routing your wires differently, and only make them as short as necessary.   Using a shielded wire for your input (only 1 end grounded) can help keep thing quiet!

Welcome to the forum, Andrea.

[andrea2127]

Hi, thank you for your advice, i work on this schematic and the pcb is the same of the picture.


It is inside a metal enclosure, so i don't that is picking any interference from outside. The screaming as you can hear from the audio sample start only when the fuzz's pot it's all way up, even if the volume's pot is half way. it's my first pedal so yep, there is a lot of long wires  i'll try to short them as i can. i used this type of jack inside a 1590B so the input/output connection it's pretty close.


I will try to put some electrical tape between the input and output and short the wires a bit, thank you again. I'll let you know if anything changes!

[Marcos - Munky]

Welcome to the forum, Andrea.

As stated, for circuits that have relatively high gain you must use wires as short as possible, keeping them as far as possible at the same time. Shielded wires helps too, but in my experience there isn't any circuit I built that required a shielded wire (the only circuit I built that requises shielded wires was a tube amp).

You can hear the noise going loud as you turn the gain up. That's because the circuit is becoming more sensitive to pick up interferences and turn them into noise.

Electrical tape won't help, because the interference is via a electromagnetical field. But probably shorting the wires will reduce the noise. Just keep in mind dirty pedals aren't necessarely dead silent, high gain circuits have audible noises and that's why people uses noise gates.

Just a few questions: are you running it from a battery or a ac adapter? Are you using a shielded guitar? Humbuckers or single coils? Anything connected to the same wall socket? I didn't believed an light in the room or a computer near my guitar or even a fan connected to the same wall socket as my amp would result in noise when I turn on my distortion pedals, until I experienced this by myself.

[GibsonGM]

Battery or adapter? BOOM.  I came back to ask that       

Check that your ground (battery " - " terminal in this case) is connected to the enclosure.  With a plug in the input jack but no battery installed, check for continuity from battery -   to the case.   Be sure that (input) jack is grounded by the enclosure.   And look at ALL the ground connections, make sure they are solid. ....the green and black wires shown in the Veroboard drawing. 

[andrea2127]

Hi Marcos, the fuzz it's running with a battery and i'm using a non shielded squier stratocaster with single coil. There are two thing near the pedal, when i try it, the computer and the valve amp that i use to plug in the guitar, can be one of those? but i don't think so, maybe are the wires's fault. GibsonGM, i don't have any connection from the ground to the enclosure, i don't know so well about circuit and i literally copy the schematic of the vero board, need to connect the ground to the enclosure?

[GibsonGM]

Hi Andrea,

The jack may be doing it by itself, so you need to check for this with your meter's continuity setting (the "beep" that tells you 2 things are connected).   That could be the 'buzzzzz', not the screaming.   

If you don't have a meter, one way to check this is to run an LED with resistor (1k will be fine) from the battery "+", and touch its cathode ( - ) end to the enclosure. If it's grounded, the LED will light.   Always test this with a plug in the input jack as that switches ground, and depending on which tab goes where, the enclosure may NOT be grounded without the plug in the jack.   

Yes, a PC or a valve amp may have powerful enough transformers inside so that they are radiating RF noise, and your pedal could pick that up as a buzzzzzz.....the screaming is probably oscillation caused by the above conditions (long wires, coupling....)...

[andrea2127]

Hello again Gibson, here a pictures of the pedal.



I have shortened the wires, they are fine or still too long and messy? As suggested I've checked the grounding and it's ok, so I tried to change the pot with a new one but nothing change. The wires are still too long? Could be a too gain transistor problem so when i turn the fuzz all way up the circuit goes into resonance? i've also used the longest guitar cable that i've to stay away from the amp and the pc but nothing change!

Any other advice, thank you again for your time buddy!

[thermionix]

Probably unrelated, but scratch this off:

[Electric Warrior]

Could be the layout. It's a common problem with silicon Fuzz Faces. Try a small capacitor between Q1B and Q1C to fix it.

[Marcos - Munky]

The wires are still too long. Try to trim them as short as possible.

Also, the non shielded single coil strat may be part of the problem too. Try to test the pedal with everything else on the room turned off. Even the lights. Well, everything else but your amp .

[GibsonGM]

Yes, you could shorten the wires.  That green one is all over, ha ha!   I use a smaller gauge of wire (maybe it's #20 or #22?). Makes it easier to route them.    Not a bad build as you are just getting started, it takes time until you just do this 'by feel'.   Keep it up.

When signal wires MUST cross each other, make sure they do so at a right angle.   Route your power wire(s) away from signal wires, along the enclosure shell, if you can.   Not as critical here as in some other applications, but good practice anyway, especially if there is an LFO involed (trem, phaser etc).   

I think Marcos is probably right, the single coils may be picking up RF (they always do!). And remember, the gain pot has signal wires all around...as you increase the drive, you increase how much signal will bleed to other wires and parts on the board, get re-amplified, and do that over and over, which makes squeal!   That feedback is 'oscillation', like a flywheel effect.