New mini-breadboard

Chuck D. Bones

Circuit Wizard
Jubal81 & I have been messing with a servo-biased Germanium Fuzz-Face. Here's my rendition. Controls are FUZZ, BIAS, TONE & LEVEL. The trimmer sets the servo's operating point. The collector currents don't drift; the servo keeps the DC component of Q2's emitter current constant.

Thanks for the mini-breadboard, Fig!

Servo Fuzz-Face breadboard 01.jpg
 
Yass!
I've been having an absolute blast with this one this afternoon. Chuck's cooked up an epic one, guys. Buckle up.

IMG-1020.jpg
 
Wow! Yours is so neat. Did you use film for C6? You should.

This started out as an experiment to see if it could be done. It's a basic Fuzz Face with an opamp and a half a dozen R's and C's added on to stabilize the operating point.
Nah, the film is C1. I used electrolytic for C6, but I could try an MLCC for that. Only had one 2u2 film cap.
 
I just put a heat gun on the transistors. Q2's collector voltage went from 5.499V to 5.788V (about a 5% change) and then settled back to 5.483V when the servo caught up. Not a very scientific test, but the servo is doing its job.

Without the servo, Q2's collector voltage would have run away.
 
Last edited:
The 3130 has built-in output voltage regulators. Is that the feature being implemented?
 
The CA3130 is a simple CMOS opamp. I'm not sure what you mean by "built-in output voltage regulators."

In this circuit, the opamp's inputs and outputs are operated near ground. Not all opamps have that capability. The CA3130 does. The TL072 does not. The requirements for the servo opamp in this circuit is that it must have very low input bias current (FET input) and the inputs and output must be able to operate at the negative rail (ground). The CA3130 is not the only opamp that meets these requirements, but it is readily available and relatively inexpensive ($2 ea at Tayda). The CA3130 shows up in other pedal designs; some by me, some by others, like Bjorn Juhl. This is the simplest implementation of the servo control. There are ways to make the TL071 work, but it takes more parts. There are other rail-to-rail opamps out there.
 
I just put a heat gun on the transistors. Q2's collector voltage went from 5.499V to 5.788V (about a 5% change) and then settled back to 5.483V when the servo caught up. Not a very scientific test, but the servo is doing its job.

Without the servo, Q2's collector voltage would have run away.
I held Q1 up against a hot tube and put it back in and got pretty much the same result.
 
I held Q1 up against a hot tube and put it back in and got pretty much the same result.
Sorry, I should have expanded a bit more. I didn't try to get the transistor hot. It felt just a bit warmer than the air. Rushed it back to the breadboard, popped it in, and the fuzz sounded the same. Yeah, not all scientific, lol.

However, in the past, I've noticed even a 5-10 degree change in room temperature can make a dramatic difference with Ge transistor fuzzes.
 
The CA3130 is a simple CMOS opamp. I'm not sure what you mean by "built-in output voltage regulators."

In this circuit, the opamp's inputs and outputs are operated near ground. Not all opamps have that capability. The CA3130 does. The TL072 does not. The requirements for the servo opamp in this circuit is that it must have very low input bias current (FET input) and the inputs and output must be able to operate at the negative rail (ground). The CA3130 is not the only opamp that meets these requirements, but it is readily available and relatively inexpensive ($2 ea at Tayda). The CA3130 shows up in other pedal designs; some by me, some by others, like Bjorn Juhl. This is the simplest implementation of the servo control. There are ways to make the TL071 work, but it takes more parts. There are other rail-to-rail opamps out there.
Sorry, I was unclear (at best). I had read the in the datasheet that one of the suggested applications for this opamp was as a voltage regulator and I somehow that translated to built-in VRs...dunno..anyway...unless I'm hallucinating it's being used as such in this case.
 
Back
Top