Maestro FZ-1S Super Fuzz - Filter / tone question

[andy-h-h]

Hello - first post...   have built a few toys recently and have just finished soldering up a Maestro Super Fuzz FZ-1S, and it sounds pretty cool.  I can understand very basic high / low pass filters, and I'm curious to know what is going on in this pedal.  What is going on with this filter - what is this kind of filter circuit called? 

Sorry if this is covered elsewhere

[Mark Hammer]

Parts of it look like a sort of highpass, but I have to wonder if it is drawn (and redrawn) accurately.  There have been a number of errors in Maestro factory schems.  Not a LOT, but things that would throw someone off if they were attempting to clone from the original factory schem, and could not spot the illogic.

I was given an original FZ-1S board, rehoused it, and it sounded great.  A nice range of different sounds.  I'd comment on the sonic effect of the switch, but it seems to be missing at the moment.  I think I loaned it out to a guy down the street.  Now that I'm retired, I'm re-organizing all my space and gear, so I may well run into it, before I start harassing the guy.

[Plexi]

It remains me, in some way, to the high-pass stage w/fixed 'value' from the Big Muff tonestack, as Mark says

[Steve.mg]

Hey, I was wondering about Q5 and Q6... Never seen transistors wired up "that" way! Not sure they'd 'do' much (?) 

Steve                   

[andy-h-h]

Think Q5 and Q6 are acting as diodes in this configuration - why not just use diodes?  I don't know...

[PRR]

> why not just use diodes?

I think at some times and places, reject transistors were cheaper than diodes.

There's also the "10 transistor radio!" which had 6 actual transistors, a dud transistor for the detector diode, another for bias, and a few dud-duds soldered on to up the transistor count. (Later an FTC rules discouraged such shenanigans.) I don't remember seeing this on guitar gear however.

[PRR]

The R-C network *appears* to put a heavy cut on bass/mids, and a sharp rise on highs.

That would probably be ear-bleed after a diode-clipper, so I too wonder about a typo.

[andy-h-h]

It most definitely cuts bass pretty hard.   I was wondering if it was some kind of 2nd order filter or pre emphasis circuit. 

[andy-h-h]

I tried another forum (electrical engineering) and the answer I received there was that without the capacitors this is a t-pad attenuator.  The capacitors / resistor part provides pre emphasis or top boost. 

I think this is two stages of top boost based at around 1k with attenuation.

[PRR]

Yes, I think it approaches 2nd order.

[andy-h-h]

I tried it on a breadboard running pink noise through the circuit and measuring the results on a spectrum analyser, and tested each stage of the filter  -  I'm pretty sure it is a 2nd order high pass filter with quite a high rolloff point (about 1k).

[PRR]

It hits 5.7dB/Oct.... simple filters don't get to 6dB/Oct until way way down/up the curve.

[andy-h-h]

Thanks - what did you use to produce that simulation?