ETI Hyper-Fuzz

[PRR]

> published in Practical Electronics

It can be found on https://worldradiohistory.com/Practical_Electronics.htm
https://worldradiohistory.com/UK/Practical-Electronics/80s/Practical-Electronics-1988-07.pdf
but the schematic does not come out well.

[Mark Hammer]

Thanks for the link, Paul.  This may be legible enough for many here.

[ElectricDruid]

What a delight to hear from the source!

+1 agree. A pleasure to meet you, Chris. Where did they get Charles from?!? It makes you feel better if you think people are actually paying attention. Doesn't look like that was the case at ETI very much. Oh, by the way, which one's Pink?!?

[iainpunk]

Im contesting Antonis, as i believe it is a buffered gain stage.
R1, R2, R3, C2 and Q1 form a stable constant current source, creating a high gain gain stage with Q3. Q2 acts as a buffer, not a Sziklai, as it has a tap point in between them where there shouldn't/can't be one for a proper Sziklai operation.

Its basically a diode ladder wave folder pushed by that gain stage.
This isn't a 'full fold' wave folder tho, its more of a wrinkly clipping threshold, instead of a 'true' fold. I have build this type of topology on my breadboard a long while ago, and compared to some of the other wave folder based circuits i built, this one is super milquetoast (which is probably a good thing for 99% of guitar players)

Cheers

ummmmm.... i'm usually wrong, BUT

a "buffer" cannot be a "gain stage" as a "buffer" is a "unity gain amplifier" unity gain being slightly BELOW actual unity gain, innit?

negative dB's are dB's nonetheless. a voltage divider is also a gain stage, however counterintuitive it might sound.

but what i meant with that was a gain stage with a buffer tacked on to its output to improve current drive.

cheers,
Iain

[Chris Dancer]

Wow that's amazing Chris! It's really great to hear the backstory on this! It's in my queue to build some time soon!

There are some things I'm still contemplating. The bias voltage is not mid point of power supply?

I'm also still trying to wrap my head around the input stage.

The bias voltage is offset from mid-point to get the maximum swing out of the LM358 before hard clipping, because its output doesn't swing rail-to-rail.
Q1 is a current source, Q3 is a common-emitter amplifier, and Q2 is a buffer. Switching from 'through' to 'effect' changes the gain of the input stage from ~1 to something higher, controlled by RV1. I can't remember why I didn't just bypass the whole circuit for the through setting, the reason is lost in the mists of time

[Chris Dancer]

Where did they get Charles from?!?

I assume they confused me with the handsome, sophisticated actor Charles Dance. Easily done.

[Ben N]

Where did they get Charles from?!?

I assume they confused me with the handsome, sophisticated actor Charles Dance. Easily done.

Tywin Lannister?