Looking for help to Mod Anderton's quadrafuzz

[Ben N]

You may be deaf; I seem to be senile. Forgot all about that, even though I commented on the thread. Sadly, the links all seem to be dead.

[armdnrdy]

I've decided to bread board Mark Hammer's "cut down" version of the Quadrafuzz that includes the filter (dual 100K pot) after each frequency band. I plan to try a few different ideas while the circuit is on the bread board.

One of the ideas is replacing the switches that Mark Anderton refers to in the PAiA PDF as "resonance controls" with pots.

The frequency bands see the switches removed and the 10K resistor (Mid 2) being replaced by a 10K pot. A 5K pot will replace the 4.7K resistor in the Mid 1 and LO bands.

When the "resonance" pot is counter clockwise it bypasses the resistance as if the original switch was open. When the pot is clockwise, the resistance is introduced as if the switch was closed.

The original HI frequency band is set up a bit differently. The original switch, switches a capacitor (C10 .047µf) in and out.
I thought to add a "mix" control using a 100K pot to "mix" the capacitor in and out but, I'm not sure what effect the added resistance will have. Maybe move the pot between C9 and C10??? Any suggestions?



Quadrafuzz original:

[maoriente]

Hi Mark,
Funny how things come back around. I remember asking you questions on this back in '97 on another message board.

I recall you also had suggested lowering the cap if/when increasing the resistors as you suggest. Was the idea to keep the 7.2khz frequency cutoff?

For instance, with 150k, should the cap be lowered to 150pf? (7.0khz)

And with 220k, cap reduced to 100pf? (7.2khz)

I have always been of the view that, as forward-thinking as the overall design was, applying the same gain to frequency-bands thathave different intrinsic amplitude levels was a little short-sighted.  Consider making R39 a little larger in value than R40, and R38 a little larger than R39; e.g., R40=100k, R39=150k, R38=200k

[Mark Hammer]

97?  Wow!  Must have been on Ampage, before the Effects sub-forum mutated into this forum, and Ampage mutated into MEF.

Yeah, I guess my working assumption must have been that Craig had picked the corner frequency for a good reason, and that if one was going to alter the gain via the feedback resistor, that one should try to maintain the corner frequency by adjusting the feedback cap.

Of course, that all assumes there is also the adjustable 2-pole lowpass filter in place.  If there IS no treble-cut control of any sort, then maybe 7.2khz is not such a great corner frequency to aim for.

In fact, now that you've got me thinking about it, maybe each of the remaining three clipping channels ought to have a different corner frequency, to complement the specific passband.  For instance, if the low band used a 100k feedback resistor, then try a 1500pf feedback cap for a (1060hz rolloff).  For a midband using a 150k feedback resistor, a 680pf cap would give a rolloff around 1560hz.  And for a high band using a 220k feedback resistor, a 220pf cap would give a rolloff around 3300hz.

Those may sound low, but note that these are 6db/oct rolloffs, so they still allow higher-frequency content through...just not as much of it.

[maoriente]

Thanks Mark

It was Ampage, can't believe it's been 17 years! You also hooked me up back then with a few old Craig Anderton articles such as the Hyperflange and Voltage Controlled Delay. I still have one SAD4096 left, hopefully I'll put it to use in a delay someday soon.

I did make a stock quadrafuzz back in '97, wasn't crazy about it, don't remember why, but I never did box it up, plus the board was huge.

I'll socket those parts and give both suggestions a try.

Mike