Superfuzz Pots

[DiscoVlad]

Just a quick question:

I'm currently in the middle of laying out a Superfuzz based on this schematic:

http://www.univox.org/pics/schematics/superfuzz.gif

The balance (volume?) and expander (gain?) pots are shown as Linear taper, I'm presuming because they were originally sliders. Is this correct? Or should one or both be audio taper?

[hairyandy]

Just a quick question:

I'm currently in the middle of laying out a Superfuzz based on this schematic:

http://www.univox.org/pics/schematics/superfuzz.gif

The balance (volume?) and expander (gain?) pots are shown as Linear taper, I'm presuming because they were originally sliders. Is this correct? Or should one or both be audio taper?

Actually they were originally pots not sliders in the Univox Superfuzz.  I don't know though if the volume should be audio taper or not.  Usually the volume pot in most circuits functions best as an audio taper.

andy

[SonicVI]

They are both linear.  I recently built one from the same layout and the knobs don't work like traditional gain and volume controls, they sortof both control volume and gain. I'm still figuring how they work together, but I'm pretty sure they don't need to be audio taper.

[DiscoVlad]

Actually they were originally pots not sliders in the Univox Superfuzz.

Learn something every day, thanks

They are both linear.  I recently built one from the same layout and the knobs don't work like traditional gain and volume controls, they sortof both control volume and gain. I'm still figuring how they work together, but I'm pretty sure they don't need to be audio taper.

Cool, that's all I need to know... Something to look forward to when it's done.

[DiscoVlad]

I managed to get the board for this built a few weeks ago, and promptly plugged it in whereupon I was treated to the blissful sound of fuzz reminiscent of an amplified jar of angry wasps nothing.

Needless to say, I was not impressed... in fact, rather annoyed as it was intended to be demoed later than evening.

Figuring it was likely to be something obvious, I put it aside... Until today...

Remembering this thread and based on my supplier having multiple datasheets for 2n2222's with different pinouts (one was CBE, the other EBC), I figured that maybe the transistors were in backwards.

This turned out to be exactly the problem.

In lieu of a guitar and amp (some of us have to work in order to finance our hobbies), I hooked it up to the signal generator (set to 100mV p-p, 1kHz sine) and scope:

This is with the "expander" (gain/octave?) pot nearly maxed, "balance" (volume?)at around 20%, and shows the octave up effect rather nicely.

More to follow later, once it's been put into a box.

For those who want to build a superfuzz like this:

Parts List:

Code Select Expand

Part Value

C3 2.2nF
C13 10nF
C2,C12 100nF
C1, C4-C11, C14, C15 10uF
C16 100uF

D1 LED
D2, D3 OA91 (any Ge)

PH1, PH2 Neutrik NMJ6HCD2
Q1-Q6 2N2222
Q7 BS250

R35 100Ω
R15, R16 470Ω
R31 1k

R6, R20 1k8
R10 3k3
R34 4k7

R8, R13, R14, R19, R25, R27, R30 10k
R29 15k
R2, R18, R22, R26 22k

R5, R9, R24 47k
R3, R4, R17, R21, R28, R32 100k
R12 150k

R11 220k
R7 470k
R1, R33 1Meg

R23 10k Trimpot
POT1, POT2 50k linear


Schematic
Some parts have been added/changed, but are only related to the power supply/indicator LEDs, so shouldn't affect how it sounds.

Board Layout

Toner Transfer (600dpi)

[R.G.]

They are both linear.  I recently built one from the same layout and the knobs don't work like traditional gain and volume controls, they sortof both control volume and gain. I'm still figuring how they work together, but I'm pretty sure they don't need to be audio taper.

The Superfuzz has several functional blocks separated by controls.

The first block, up to the expander control is a preamp. It provides a bigger guitar signal to the expander control, which lets through some percentage of the amplified signal. The third transistor is a phase splitter, produces two equal-and-opposite signals into the two bases of the fourth and fifth transistors. The fourth and fifth transistors are a full wave rectifier. They work by the transistor with the most positive-going signal on its base controlling the signal at the joined collectors. Since this happens on alternate half cycles, a similar signal appears on the collectors for each half cycle, effectively full wave rectifying the AC signal. This is similar to the FWR in the Blender, Fox Tone Machine, and Green Ringer, but done with transistors instead of diodes. Because perfectly matched transistors give the best octave effect, the 10K control was included on some but not all versions of the SuperFuzz. There have been at least five versions of this circuit in different brands. This pot really is a balance control for the two octaving transistors. Balance was an internal trimpot on some but not all models. It's function is to get the best (most?) octave effect, and it was never a front panel control until the SF was worked on by the people here, Mark Hammer being the first proponent I remember. After that , the signal is clipped by the diode pair, and routed through either the attenuator or the mid scoop, and that is fed to the "balance" control to set up how much signal goes to the last transistor gain stage.

"Expander" is indeed a gain control as in most fuzzes, as it controls the signal level to the rectifiers and clipping diodes. "Balance" is indeed a volume control, determining how much signal drives the output amplifier's fixed gain. The unnamed 10K trimpot really is a balance control. I think the idea with "balance" was that it balanced the amount of fuzz output against the dry/bypassed signal..