Yet another question about the fuzz face

[shredgd]

I have built a silicon fuzz face which sounds very well, but squeals when the volume pot is set past 2 or 3 o'clock. It is correctly biased (I also tried to vary the bias trim pot to see if I could find a value where it didn't squeal, with no success).
I don't think I'll ever use such a high volume pot setting, but I would like to have a 360° properly working pedal nonetheless. Or is it another of the fuzz face "structural" problems (as the "guitar volume pot set to zero"-related issue)?
Thanks

Giulio

[kroushl]

Are the input and output jacks physically close to each other? This can cause oscillation at high gain.

Brad

[ErikMiller]

Mm, yes, oscillation in a high gain silicon Fuzz Face.

I've had problems with this. What construction technique did you use?

They can be sensitive to parts layout and construction technique. VERY sensitive.

I've cured oscillation from bad layouts in the past by switching to a different cap type for the output. Film, monolithic, etc.

Dunlop used to stick a 47pF cap on the feedback (100K resistor) line; I don't know if that fixed it or if they were just shotgunning it.

[Gearbuilder]

Hello,
Humm a squealing Fuzz-Face?What transistors did you used in it?
I've see some BC  109 good for making squeals at low fuzz settings .
Maybe they have too muchhh gain?

Bruno

[Ammscray]

Where is your fuzz pot set? You know that with a silicon FF you can't have both the volume and the fuzz pot turned all the way up, without serious oscillation...if your fuzz pot ISN'T all the way up, I suspect a bad layout, or your input or output wires are too long...

[ErikMiller]

Where is your fuzz pot set? You know that with a silicon FF you can't have both the volume and the fuzz pot turned all the way up, without serious oscillation....

Not true. I've built many a silicon fuzzface, and the only oscillation problem I've encountered is one that rides on top of the signal. It's not there when no signal is running through the effect. This can be cured with studious attention to layout.

I build 'em with some seriously high gain, too. :-)

[Ammscray]

Where is your fuzz pot set? You know that with a silicon FF you can't have both the volume and the fuzz pot turned all the way up, without serious oscillation....

Not true. I've built many a silicon fuzzface, and the only oscillation problem I've encountered is one that rides on top of the signal. It's not there when no signal is running through the effect. This can be cured with studious attention to layout.

I build 'em with some seriously high gain, too. :-)

Not true?? What does that mean?? I'm lying?? :?

[ErikMiller]

Not true?? What does that mean?? I'm lying?? :?

Nope, merely that there is information of which you were not aware that is contrary to your belief.

[B Tremblay]

It would be great if you could share that information with the forum...

[shredgd]

I'm using two BC108B with about 300 and 320 of gain.

The squeal occurs when both fuzz and vol pots are set to max or nearly.
(To be exact, considering max=5 o'clock,
I have to turn the fuzz pot to 4 o'clock to make the noise disappear when the vol pot is set to max
I have to turn the vol pot to 2 o'clock to make it disappear when the fuzz pot is set to max)

The squeal, when it occurs, is there if I don't play anything (when I play there's no noise, but it comes again as the notes decay) and even if I stop the strings.
It disappears when I close my guitar volume pot, though (then I might catch some RF, but that is a normal fuzz face "feature", isn't it?)

I made the layout myself, and the circuit sits together with a rangemaster and a mosfet booster... Yes, three pedals in a box, each engaged via a DPDT toggle switch (wired exactly as you would wire a DPDT stomp switch for true bypass and input grounded when the effect is off), with a "master" stompswitch to "engage the box", whatever effect is on (I previously decide it via the toggle switches).
Therefore, there's quite a bit of wires in it, some of which run along the box from the stomp switch at one extreme to the jacks and the toggle switches at the other extreme. I tried to move them and the squeal does vary a bit, but it doesn't disappear.
[now I have another question, too: why does noise (another one) appear if you touch the wires (even if they are isolated ) with your fingers? I thought that, at most, your body should act like mass!]
The input and output jacks are at the front of the box, which is quite big though, so the tips of the jacks are as distant as in a Boss pedal, not that close to each other.

The fact that even merely the layout of the circuit might be the problem is...  SCARING!!

Giulio

[ErikMiller]

It would be great if you could share that information with the forum...

?

I've never built a silicon FF (and I've built dozens) either on perfboard or printed circuit board that squealed when the knobs were dimed.

I also never heard such behavior described as common knowledge until Ammscray did so.

Of the silicon FF build pages I've read, none warn the builder not to turn the knobs all the way up lest they squeal, none of the reviews I've read mention this phenomenon. Is it really universal or even common? Dallas-Arbiter, Crest, et al put out a fuzzbox that you can't dime the knobs on without it squealing?

As for how to make it not happen, I can only suggest moving the components and wires around and seeing what happens.

Shredgd, what value and type of capacitor are you using at the output?

[Ammscray]

Not true?? What does that mean?? I'm lying?? :?

Nope, merely that there is information of which you were not aware that is contrary to your belief.

I'll tell you what mr master builder, I was playing original silicon fuzz faces before you knew what an input jack was, and building them along the way for just as long...the problem that Shredgd is speaking of when the controls are cranked is characteristic of the silicon version because of the high gain, and it's not new news at all...I suggest that you've never built one right, or probably never used authentic NOS transistors...or maybe you're just another wiseguy newcomer, or all three, whatever :roll:

[Ammscray]

I'm using two BC108B with about 300 and 320 of gain.

The squeal occurs when both fuzz and vol pots are set to max or nearly.
(To be exact, considering max=5 o'clock,
I have to turn the fuzz pot to 4 o'clock to make the noise disappear when the vol pot is set to max
I have to turn the vol pot to 2 o'clock to make it disappear when the fuzz pot is set to max)

The squeal, when it occurs, is there if I don't play anything (when I play there's no noise, but it comes again as the notes decay) and even if I stop the strings.
It disappears when I close my guitar volume pot, though (then I might catch some RF, but that is a normal fuzz face "feature", isn't it?)

I made the layout myself, and the circuit sits together with a rangemaster and a mosfet booster... Yes, three pedals in a box, each engaged via a DPDT toggle switch (wired exactly as you would wire a DPDT stomp switch for true bypass and input grounded when the effect is off), with a "master" stompswitch to "engage the box", whatever effect is on (I previously decide it via the toggle switches).
Therefore, there's quite a bit of wires in it, some of which run along the box from the stomp switch at one extreme to the jacks and the toggle switches at the other extreme. I tried to move them and the squeal does vary a bit, but it doesn't disappear.
[now I have another question, too: why does noise (another one) appear if you touch the wires (even if they are isolated ) with your fingers? I thought that, at most, your body should act like mass!]
The input and output jacks are at the front of the box, which is quite big though, so the tips of the jacks are as distant as in a Boss pedal, not that close to each other.

The fact that even merely the layout of the circuit might be the problem is...  SCARING!!

Giulio

Ciao Shredgd, it's possible you're having some problems because of excessive wires and the fact that you've got all 3 pedals in one box...but ALL silicon fuzz faces do what you've described...original issue, crest audio, whatever, if they don't squeal when the controls are dimed, then there's something wrong the the unit...most people use the silicon FF with either the volume down and the fuzz all the way up, or vice-versa...

The only real way to tell if something else is happening however, would be to isolate just the FF circuit in a box by itself...you MUST keep the wires very short and I would suggest shielded cable (at one end only)...also make sure the metal cases of the two transistors aren't touching each other...Buona Fortuna!

[Kleber AG]

B Tremblay wrote:

It would be great if you could share that information with the forum...  

Erik, I think that what B Tremblay asked is about what you have been telling us in more than one thread that you have a solution or a PCB layout that could cure the squeals issues on silicon Fuzzes, and it really would be great if could share that info with us instead of just been reffering to...

I mean no offense at all, I just really hate any discussions that sometimes gets a little "nasty", in fact I may just shut up, I almost can't write in english...
But, PEACE guys, let's have fun, "share" ours thoughts what may really be what this forum is about...

Regards
Kleber AG

[Luke]

Hi guys,
Please dont get upset. I for one have recieved great advice from both of you, and I sincerely respect both of your abilities as stompbox builders.
I dont have any input on the squeeling on the ff- you both know alot more about these sort of things than me- unfortuanetly, I am generally an advice seeker around here (as opposed to an advice giver)- so I really hope I dont sound out of line, but you are both great contributors here- lets all be friends- we are all into the same sort of stuff (stompboxes) and its such a great site to hang out with likeminded people.
Lets get back to building some serious pedals, eh boys?
Take care,
Cheers,
Luke

[Stuart]

For the record, my original silicon FFs don't oscillate when both controls are turned up, neither has any of the clones I've built.

[petemoore]

Now I HAve noticed that when I put numerous ckts [especially high gain ones] together in the same box [Rangemaster you say...both the Rmaster and the FF are known as great antenna/reciever/amplifiers], I've definitely noticed noise/oscillation/etc problems.
  I would second the recommend of isolating and shielding the FF...I never really had incurable problems much with FF Oxcillation [doesn't say much cause maybe I get lucky], still I think' High Gain Si FF's [and I have tried a 'few'] can be made non osclillatory with just decent layout and fairly short in/out wires.
 Of course, rarely [if ever] do I find both knobs all the way up.
 1rst on my list of possibale culprits is the 3 in a box thing...I have a LPB!/FT70 both sharing a house, and they don't oscillate, but there is 'some' noise...
 I pin the signal lines to ground planes [grounded sides or bottom of metal box] and keep em short...by considering such when planning the box layout.

[Gearbuilder]

Hi, again
If there's anybody here yet
I said on a last post that some BC with metal can or high gain are bad for FF,too much noise.
  Try other trannys on sockets ;you will see the difference
 Feedback squealing occurs often  when there's too much gain or a mistake in the layout or a bad grounding(use shield wire for the input)
One day when i'm repairing  a Marshall high amplifier ,the same squeal appeared when i touched the red wire away from the chassis;i put it close to the chassis and feedback disappeared.
Try to take back your PCB from the box and short all the wires ,

It make me laught,people here are cool ,we can give solutions with peace .
       
Bruno

[Dai H.]

I thought the squealing (unless you turned down the "Fuzz" control) w/the Si FF was normal. Well, at least w/the one I built. The purported "'70" pedal circuit didn't seem to do it though.

[B Tremblay]

Erik, I think that what B Tremblay asked is about what you have been telling us in more than one thread that you have a solution or a PCB layout that could cure the squeals issues on silicon Fuzzes, and it really would be great if could share that info with us instead of just been reffering to...

That's exactly what I was attempting to say.  I apologize for being vague.  I'd be very interested in an oscillation-proof layout.