Fuzzface switch

[angelodp]

Hi, I have recently made a fuzzface, loosely based on the Fulltone 69. Its great but the switch is dropping signal for a 1/2 second when i go to fuzz. Its fine the other way around. Any help much appreciated. 

[thetragichero]

I have the same issue with a Brian may treble booster I made forever ago: I stomp on it and it seems like it swells in. I'm wondering if I'm switching power instead of just signal (quite possible). only other thing I could think of would be a cap needing to charge up

got schematics /diagram of your switching situation?

edit: your picture just loaded

[thetragichero]

does the circuit input *need* to be grounded in bypass mode? I think that's what is causing it because at the moment you switch it on, your output goes from a bypassed signal to the output of a circuit that hasn't been passing any signal. I bet the switch pops, too, huh?

I think I am along the correct line of thinking but wait for some other guys to look at it

[JohnH]

I reckon the lower end of the R22 fuzz pot should be grounded. Here's a similar circuit:
fuzzcentral.ssguitar.com/fuzzface.php

[reTrEaD]

Hello angelodp

I agree with JohnH . Some of the other deviations from the original design are likely to be okay. But there are two which look like potential trouble. The connection of collector of Q1 to the collector of Q2. Collector of Q1 should be connected to the base of Q2 instead. Also the end of the fuzz pot should be connected to ground. Else you have no path for DC bias of Q2.

[blademaster2]

Yes, that end of the potentiometer needs to be grounded for biasing, otherwise it only biases the transistor Q2 with leakage current from the capacitor and whatever it can draw from the 100k resistor on the base of Q1.

When the potentiometer is adjusted to zero this capacitor is bypassed. It actually looks like something is still odd there, but I would need to look into it more closely to see what might be different from what I usually see. Often the single-ended 9V power is split for opamp circuits, and capacitors like these are used to AC-ground the signal while maintaining the mid-point DC level as the bias ground. With this circuit, having no op amps in a feedback configuration, the bias might be changing all the time with different adjustments and capacitors like this are needed to maintain a zero-DC-bias level for the audio signal.

And yes, it looks like the base of Q2 needs the signal from the collector of Q1 and cannot be left open.

Does that make sense to everyone out there?

[angelodp]

So sorry I had a bad schematic. It does have the recommended changes already and has the problem.

[Yogi B]

Oct 12, 2018 14:44:35 GMT -5 reTrEaD said:

Some of the other deviations from the original design are likely to be okay. But there are two which look like potential trouble. The connection of collector of Q1 to the collector of Q2. Collector of Q1 should be connected to the base of Q2 instead. Also the end of the fuzz pot should be connected to ground. Else you have no path for DC bias of Q2.

Yes the schematic was wrong, but how would've either of these things caused the described effect? Also how would it still be "great" otherwise? With Q2 wired as originally shown you'd be lucky to get any output; with the fuzz pot ungrounded it'd sound horribly miss-biased.

Oct 12, 2018 12:39:57 GMT -5 thetragichero said:

does the circuit input *need* to be grounded in bypass mode? I think that's what is causing it because at the moment you switch it on, your output goes from a bypassed signal to the output of a circuit that hasn't been passing any signal. I bet the switch pops, too, huh?

I think I am along the correct line of thinking but wait for some other guys to look at it

But it isn't grounded, and that's the problem it's connected to (B) -- the negative side of the battery -- that isn't ground.

In bypass mode the 2n2F input cap would be reverse biased, the time taken for the charge to re-orient back the correct way being the cause of the delay. Also, if you've actually used a polarised capacitor, it's now likely damaged.

---

I can see why some people like tantalum caps now: if there's an error in your circuit they're all so bursting with excitement to clue you in, that they just can't help but go pop.
... or something ...

[angelodp]

This is a PNP Germanium setup and the effect is wired correctly, but the switch is the problem. It does sound very good with all controls working, its just misses a beat when switched into Fuzz?? Perhaps the switching method needs re-working.

Thanks

Have to go out for a bit and can continue in a few hours. Appreciate the responses.

[Yogi B]

Oct 12, 2018 19:36:41 GMT -5 angelodp said:

Perhaps the switching method needs re-working.

Yup, though it would've been helpful if I'd actually suggested the fix in my previous post, wouldn't it...

For the switch wiring, (A) and (B) need swapping and the LED needs flipping.

[angelodp]

Ok just that simple. I’ll try it.

Thanks

[angelodp]

Yogi B, Bravo, Bravissimo. That did it. You are one clever fellow and so helpful. It works as it should. I will post the revised schematic and build pics shortly.

Many Thanks.

Ange