Exar SF-02 Super Fuzz [schematic]

[VitaliiBobrov]

Another Exar pedal trace, Exar SF-02 Super Fuzz. I was lucky to have a friend in Austria who helped to get this one for a reasonable price. The unit seems to be produced in 1997 or later, as the latest date on the potentiometer was '97.

Exar SF-02 Super Fuzz

PCB is standard for series 2 Exars - single-sided, visible in the light.

Exar SF-02 PCB bottom

Exar SF-02 PCB top

Before tracing, I played with the pedal, whose active EQ was hard to dial for good tones but possible. My initial thought was that it has active parametric EQ, but later it appeared that it is not

So the effect structure is the following: FET buffer, BJT gain stage, op-amp gain stage, and diodes clipping. A pretty similar arrangement for Boss DS-1, with differences in values. However, diodes seem to go through a 10uF cap which is a bit strange, but I double-checked that. Then it comes to the most exciting part of the circuit - EQ, which I haven't seen in any pedal before. After the diodes clipping signal goes through the op-amp buffer/splitter. One half is a Big Muff tone stack with a boost stage placed after; another half is a kind of an active bandpass filter; both are controlled by dual Frequency pot and share the same values. Equalize pot acts as a mixer of both halves.

I made a SPICE simulation in CircuitLab https://www.circuitlab.com/circuit/ymr6 ... uper-fuzz/ to check where I traced everything correctly, and it looks like it works. Fascinating EQ circuit good platform for mods IMO. With some modifications, I would try to use it with other fuzz/distortion circuits.

Attached is the schematic with buffered bypass switching omitted.

[WrmZ]

hi VitaliiBobrov,
thanks for schematic, in past (like 15 years ago) i tried to reverse engineer this pedal but i failed

I compared shematic with my own superfuzz and it seems that you got error with R27 and R13 (on schematic those are marked as 2k3) i got 12k there

for mods
i liked opa2604 in place of u1 tantalum 10uF C5, and germanium diodes because circuit was quite noisy with silicons as i remember
C6 -> 220nF (fat) and all electrolytic 1uF -> 10uF

I will prepare pcb for this awesome pedal

[VitaliiBobrov]

hi VitaliiBobrov,
thanks for schematic, in past (like 15 years ago) i tried to reverse engineer this pedal but i failed

I compared shematic with my own superfuzz and it seems that you got error with R27 and R13 (on schematic those are marked as 2k3) i got 12k there

sf3.jpg


for mods
i liked opa2604 in place of u1 tantalum 10uF C5, and germanium diodes because circuit was quite noisy with silicons as i remember
C6 -> 220nF (fat) and all electrolytic 1uF -> 10uF

I will prepare pcb for this awesome pedal

I've just checked it out, and you're right - for some reason I read those on the opposite side - probably thought the brown one is gold and stands for tolerance . I've uploaded an updated schematic to the first post and updated CircuitLab model as weel. Thanks!

[VitaliiBobrov]

Updated schematic version with fixed tone stack values:

exar-sf-02-schematic-v1.1.pdf

Exar SF-02 schematic

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