Yet another question about the fuzz face

[shredgd]

Thank you very much for all your replies.
I don't think I can change much in my pedal, it was born "this way"... (actually, it sounds very good and I don't need that "extreme" setting)
However,
Erik: I used a 0.1u poly film output cap. I'll try and see if that 47p cap on the feedback line improves the thing.
Ammscray, Pete and Bruno: I'll try shielded cables. Will a shielded input cable be enough? Or where else?

Gearbuilder wrote:

Feedback squealing occurs often when there's too much gain or a mistake in the layout

What, in a layout, can be cause of oscillation?

Thanks again,

Giulio

[petemoore]

Depending on transistors, gain settings, frequency shaping [cap values] pickups, amp, anyother edkts in the chain XP2etceteras FF's will widely vary...one characteristic may change another...say gain Vs oscillation for one.
 It seems plenty easy to go 'over the top' with many of the characteristics of the FF [except high end response I say?].
 With three ckts in a box [one of them a high gain ff], the noise/oscillation may easily get out of hand.
 So I submit Ff is a widely tunable ckt., and the 'trick' to happy FF usage lies in finding a tuning within it's capability that you can use and like.
 'Some' experimentation may be necessary [I know I did countless hours of it].
 I built some fixed value FF's, but soon opted for more tunable board with trim for Q2 sockets for caps and tranny's [and maybe another 'fixed' Resistor].
 Is the theory: >"aving a gain ckt powered and bypassed may lead to noise when it's boxed with another gain ckt that  is not bypassed?"<
                 ...Right or wrong in Your experience?_____

[ErikMiller]

Ammscray-

Whoo! Didn't mean to stomp yer toes. My girlfriend pointed out that my "information of which you are not aware" reply to you could be taken as kinda supercilious, for which I apologize. I was actually trying my damndest to just say politely (if you can believe it) that I was NOT accusing you of lying, that I just had a conflicting observation. Oh well. Ironic in a forum dedicated to TONE that I failed to get my conversational tone across.

This wouldn't be much of a place for learning if everyone already knew the same stuff, and I appreciate finding out about a characteristic of some silicon Fuzz Faces of which I was not aware.

B Tremblay-

I'll post in a new thread about PCB layout philosophy. I'd rather retire from this one.

Stuart-

Thanks for the input (jack:-). I've learned a ton about both Fuzz Faces and Cry Babies from your site.

See y'all in another thread....

[shredgd]

Sorry for the big delays in my posts. I'm studying hard, so I have very little time, and I'm on a dial-up connection...

Pete, I've done some headphone testing today, comparing the little background noise (hiss) of each circuit (when set for the maximum gain) with and without the other circuits' transistors on place (this should have worked to make them not powered) and I noticed no differences. So, in my experience that theory is wrong!

I also tried a 120p cap (instead of Erik's suggested 47p - it was the first value I picked up) in the feedback line, parallel to the 100k resistor: I connected it via "crocodile wires", actually momentarily creating a loop which enhanced the squeal until everything was connected. There still was the original squeal, nontheless, but probably if the cap was soldered into the circuit the noise would be at a lower level. However, what effect would it have on the fuzz sound (I forgot to notice myself...)?

I then tried to simulate a shielded cable by rolling some alluminium around the input cable and connecting it to ground, again via a "crocodile wire". Again, it was difficult to quantify things because the pedal was open, but I'm almost sure that using a shielded cable for the input should at least improve the squeal issue.

I must say that today the squeal was way quiter than the past day... the thing starts to get even more complicated!
Unluckily, as I wrote, I have very little time to play, so I can't do that extensive testing. Actually I think I'll put off any further speculation and any decision to make mods to the pedal (which, once again, is perfectly working as it is, in the common settings range) until March.
Thanks a lot again!

Giulio