Why won't my fuzz oscillate?

[colossus]

This is not my first pedal. I've done probably 15 builds at this point, and the majority from schematic --> vero. But this is a silly, probably insanely basic problem that is bothering me. I just built a bazz fuss for the fuck of it and I'm trying to add momentary oscillation (which I have done w/o a problem before with another bazz fuss) via the most basic feeding of the output back into the input. AND it's not working! It just cuts the signal entirely. Please tell me what horribly stupid thing I'm not doing correct right now.

Lead from output tip to input tip just cuts the signal. With a pot in between, it attentuates the cut and gives me some of the effect.

[culturejam]

If you connect the input cable to the output cable, you just shorted the whole circuit and basically made a bypass route.

I would try taking the output of the bazz (before the volume pot) and feeding it back directly to the transistor's base pin. This will put the feedback point *after* the input cap.

The bazz is harder to do oscillation with because it has so few parts and only one amplifier stage.

[colossus]

Tried that and no dice. I swear I got one of these circuits to oscillate fine without fail before.

[culturejam]

Maybe you need more resistance in the feedback loop.

[colossus]

I'll keep playing. Thanks man!

[crochambeau]

Bear in mind that if the over all circuit inverts polarity between input and output, feeding it back upon itself will work *against* oscillation.

[culturejam]

Bear in mind that if the over all circuit inverts polarity between input and output, feeding it back upon itself will work *against* oscillation.

Great point.

Bazz Fuzz is a single common emitter amplifier, which does invert phase on the output.

[KaosCill8r]

I'm not sure but would the Bazz Fuss oscillate by lifting the ground from the circuit? I tried this method on a Meathead curcuit and it worked well. Never built a Bazz Fuss so I don't know if it will. Worth a try and it's a lot simpler than a feedback loop.

[skullservant]

Bazz Fuss circuits are super hard to get to have decent oscillation. If you put two in a row though, it is easier

[colossus]

Bazz Fuss circuits are super hard to get to have decent oscillation. If you put two in a row though, it is easier

Yeah...that makes sense, as I've had no problems getting a buzz box to oscillate.

Can someone explain the matter of inverting phase on the output? I get why that will work against oscillation, but what makes something invert phase, i.e., how can you tell?

[culturejam]

For transistors, a common emitter amplifer (output comes from the collector), the output is 180 degrees out of phase with the input. For a common collector amplifer, also called "emitter follower", or more commonly know as a buffer, the output is in phase with the input.

A great example of this in action is the basic Univibe phase stage. There is an LDR (light-dependent resistor) that is going from high resistance to low resistance (driven by a bulb, which is modulated by the LFO). When the resistance of the LDR is low, the output of the transistor is coming from both emitter and collector, so the signal is partially in phase with the input. When the resistance of the LDR is high, output is only coming the collector, which is totally out of phase with the input. So as the LFO sweeps, the audio goes from being somewhat in phase to totally out of phase, and that's what gives you the vibe sound. If you have some dry signal mixed in at the output, you hear phaser sounds. With no dry for reference, our ears perceive the phase shift as a very very short delay, and as you modulate delay time you get.....pitch bend!