Questions about Inductors, Transformers, & Fuzz Impedance!

[tatou]

I was just skimming the new MBP offerings and studying the VFE Fuzz Duo schematic.

This circuit includes an inductor in series with the input, which reminds me of the transformer in front of the FolkUrban variant of the Bazz Fuss, which in turn is nicked from this AMZ article on Guitar Pickup Simulation.

Still learning EE basics, so a few questions:

• Does the inductor in the Fuzz Duo serve the same purpose as the FolkUrban/AMZ transformer (and is a transformer really just two inductors)?
• That is, does it adjust input impedance to help the fuzz function well after buffered effects without losing tone?
• If so, why is an inductor better at raising input impedance for this use case than a resistor?
• If not, what does the inductor do?
• What about the two inductors to ground off the Q1-Q2 emitters?
• How does one select the value of an inductor/transformer for this purpose?

I've got an experimental "fuzzstortion" on the breadboard right now and wondering if adding an inductor or transformer would help it play well with other effects. I don't have either of these in the parts stash, so wondering if it's worth a Mouser order to play around with...

Thanks!

[madbean]

Those are great questions which I asked myself when I started working on the project.

As far as I can tell the inductor at the input serves to reduce high frequency noise and perhaps some added benefit of further isolating the circuit like you mentioned. It does seem to respond really well to loading IOW when the guitar volume is rolled down - esp. with the GE transistor.

On the emitters I am less sure. At first I thought maybe it helped with temperature stabilization but there wouldn't be a need for that on Q1. Since Q1 on a FF is usually connected directly to ground perhaps the answer is the same - the very low resistance of the inductor is about the same as connecting the emitters to ground but has some side benefit (the reactance of the inductor, maybe? I dunno.)

I haven't quite put it all together so maybe someone else can enlighten us.

I am also still perplexed by my low Q2 voltages I recorded in the doc. It might be I just have a very leaky/bad AC127 for that first stage transistor. But, it is definitely the right reading. I think I'm going to get a couple more NPN GE when I make my next smallbear order and see what happens. It sounds like a well balanced fuzz IRL but some parts of the circuit are, err, fuzzleling.