Silicon Fuzz Face - OSCILLATION

[Barracuda]

So, I have followed the Fuzz Face Silicon Circuit, and compared it to a few others, like Madbeans Hipster pedal and the like. Heres the one I used...


I started this on breadboard with 2n4401s, but I had tried 2n2222s and have now swapped to 2n5088s, with no noticeable difference..
I have now soldered this on perfboard, but I'm getting oscillation - "dolphin noises" no matter what I do. I have tried caps between Base and Collector on both transistors at the same time with no luck. I have tried resistors between transistors to weaken the gain with no luck, and swapped a couple collector resistors, even when I back off the fuzz knob, it still oscillates. This leads me to believe it is not the circuit thats the problem, but possibly a component or something of the sort.

Here are the voltages I'm getting (I know that Q2's collector is biased way off, but should that be causing oscillation??)

Q1
E  =  0
B  =  0.53
C  =  1.62

Q2
E  =  1
B  =  1.6
C  =  1.8

(These were on breadboard with the 2n4401s, but even on perfboard with 2n5088s, they are very similar)

https://www.dropbox.com/s/ia0cvgnjj7z3w44/20170107_195948.jpg?dl=0



Check this audio sample out, you can hear me back off my guitar volume, and then the fuzz knob soon after...
https://www.dropbox.com/s/b0k9465pf14yc5u/Oscillation.mp3?dl=0

This is on perfboard, so I don't think I can blame the breadboard or anything around that as its making exactly the same noise as it did on breadboard. I used the 2n5088s, they were from China on ebay but I'm not sure how much that would affect anything? Theres no volume pot if that changes anything, but I tried a 100k on the breadboard just to see if it helped, it did not. Also the ceramic 10nf capacitor is TINY, could this be a result of it not being able to take the voltage/current? I'm not sure on the power rating of it.

If it isn't the transistors, all I can think to blame are my ceramic caps which I don't entirely trust, or my jacks, which are meant to be stereo, but don't look like any other stereo jacks I've seen. But I can't imagine them causing oscillation? this has been bothering me for months, thought it would have been a more common occurrence, but if it isn't, then surely I have something bad? I don't like blaming equipment, but I've shown you what I've done and if everything looks as though its in order, what is there left to blame?

[Ralfg]

Could it be a grounding problem? Or some solder that is connecting something that shouldn't? Do you have some pictures? Maybe you can turn this into a cool "feature"

[midwayfair]

what are you powering it with, and if it's a wall wart, did you add power filtering (see the Hipster for reference)?

[Aleph Null]

1) Try a different power source (A battery is always the cleanest).
2) Check for unintentional grounding.
3) Test and/or replace the transistors. Dolphin calls = bad transistor in my experience. I think this is most likely, but I mentioned the other two steps first because they won't cost you any money.

[Barracuda]

I think its bad transistors, I got all of mine from the same supplier in china on ebay, so maybe thats why they all oscillate... I am powering it with a battery at the minute just to eliminate the fact there could be mains hum. I know I've wired right because its making exactly the same sound on perfboard as it did on breadboard! The things currently connected to ground --

In/Out jacks (ground lug)
Q1 Emitter
Bypass cap
Negative battery
1st lug of potentiometer (3rd lug connected to Q2)

[midwayfair]

Thanks for adding the sound sample. Does the frequency of the oscillation change when you change your guitar knob's settings? Does it go away if you turn the guitar down all the way? Does it change with the location of the fuzz control?

Have you tried fixing the bias on the collector of Q2? It's way lower than it should be, and especially low given that if you used the traditional values that your modern higher gain silicon transistors, which have higher HFE than old ones, should bias much closer to 6V. This could indicate that you have a wrong connection or pinout, some wrong resistors, or something else.

I'm not exactly sure what kind of "bad" a transistor would have to go to create that noise, but you should systematically eliminate other issues.

[Barracuda]

Hi Midwayfair, I've seen a few posts you've made before about FF's and they were very helpful, so thanks for that because they were all things I considered when making/testing this one.

I've heard all nightmare stories about oscillation on breadboard so that's why I've perfboarded this one after it oscillated on breadboard, just to eliminate the fact it could've been caused from building on breadboard. I eliminated a few other factors like using mains and basically everything I can think of. I did have a potentiometer on the bias and even at 4.5 it was making the same noise. I've made this circuit on breadboard multiple times with the same result, even with the bias right (this was a while ago). It seems I get oscillation no matter what circuit I build, even when I've built gated type fuzzes they still have some oscillation going on in the background. I double checked the pinout, its all correct. One transistor won't oscillate on its own, but two will.

Yes, if you listen to the sample, you'll hear me roll my volume down at about 0:14, and then soon after fiddle the fuzz pot. I double, infact, triple checked the resistors when I was breadboarding it, and even fiddled with a couple values like the feedback resistor. I'll either get little to no gain/fuzz or I'll get oscillation. I've tried caps between both q1's and q2's collectors and bases, at the same time too, they just cut some high end off, but not the oscillation.

I've ordered some new transistors which should be here in 2-3 days, AC128K's (dont know the hfe, woops), and some BC108's with a 10nf cap that I KNOW will take the voltage of the circuit (100V cap), whereas these ceramic caps were very tiny and I don't know if they could take the voltage, but then wouldn't it just not pass signal through? Something that might be interesting is when I've swapped the output cap to 100nf and the oscillation got deeper, but I know that the capacitor was 63V. If there's anything I can try before the new parts come I'll try it! But if I get the same problem, obviously there's something very wrong. Can wiring jacks up wrong cause this? I have stereo jacks, but not like any I've seen anywhere else, they pass signal through consistently though.

Thanks for the replies!

[Ralfg]

Are you grounding your jacks?

[Barracuda]

Yes, I might try and change the ground lug wiring though as the layout is confusing on these jacks, they're different from all the diagrams/images I've found

[Barracuda]

So I tried swapping the ground lug wiring and got just squealing with no guitar coming through.. So obviously that can't be it. Would it make a difference if i was using the right or left input?

[Ralfg]

Just thinking through your last post, with the change to the oscillation tone by swapping a cap. Do you have an audio probe? Check the circuit to see where the oscillation starts.

[Barracuda]

Hey Ralf, I don't have an audio probe unfortunately I have tried using these transistors on their own, and they work, but never when I've had more than one on a circuit, that's when I get oscillation. I've tried a few different fuzzes with them and had the same result.

[midwayfair]

I want to see the layout you used, and pictures of the perfboard and your off-board wiring. Your breadboard looks fine.

Audio probing a fuzz face isn't necessarily super useful. You can check the base and collector of Q1, otherwise what you hear is what you get.

Hfe is not really important to this problem. High HFE is more likely to oscillate, but not this noise. It's usually just a high pitch, and it's actually likely to be from the power source, which is why a 22pF cap is sufficient. (In cases where it's not the power source, it might be some bleed between the input and output connections on the footswitch, but you have to have extraordinarily high levels of gain for that.)

The caps you used SHOULD have their voltage rating on them. Ceramic might drift, but even very tiny ceramic caps are likely to be well above a 9V rating.

A breadboard is worse for picking up interference, but they typically suffer from higher capacitance (which just as often as not means that a breadboarded circuit is LESS likely to oscillate). I had a look at your breadboard, though, and you aren't using any parallel tracks, so I would be extremely skeptical that your breadboard is causing positive feedback.

Here's what I'd do on the breadboard:

1) Ground the input (you can just alligator clip the input jack tip to its sleeve). This will kill any input to the circuit and guarantee that you are not producing positive feedback from the input. If you are still getting squealing, your problem lies in the circuit.

2) Move the 100K feedback resistor from the emitter of Q2 to the collector of Q1. This will likely misbias the effect but that's okay. We're just trying to remove a possible source of undesirable feedback. You can also change it so that it's the 100K to ground and add a 220K (or whatever) going from the base to +9V. This fundamentally changes the effect, but again, we're trying to eliminate feedback throughout the entire system.

3) Flip the transistors, just in case you did get some mismarked transistors and they're the opposite pinout.

That's all I can think of that you can do before the other transistors come in.

[Barracuda]

The perfboard is laid out terrible, as I really just did wack it together as I went along. But I know its not done wrong/any different to the breadboard, cause the noises are identical to when it was on breadboard. When I tested if it was a ground lug wired wrong, I swapped the ground wire to another lug and got no guitar signal coming through, but still a squealing noise, I don't know if that means anything...

I did also flip the transistors when it was on breadboard, I think I can remember it just having little to no gain, and swapped transistors a few times (2n2222 and 2n4401) but I will try this again aswell as the other ideas.

[mjg]

I've done really similar builds to your layout - only difference is I used a 0.1uF cap instead of 0.01uF, and I use 2n3904 transistors.   I'm not convinced that difference will be making the dolphin noises though...

Here's the schematic I have used with success, if you want to compare:  http://www.muzique.com/schem/fuzzface3.gif