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previous: Roger What I mean is that from what I can... -- 11/17/1999 5:32 PM View Thread

Re: speaking of Super Distortion/Feedbackers

11/18/1999 10:57 AM
GFR
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Re: speaking of Super Distortion/Feedbackers
OK.  
 
To increase the depth try increasing C36 and/or decreasing R62 or R60. The LFO is mixed to the "loop error" signal at pin 9 of the 4046 PLL. You need to increase the amount of LFO that gets mixed.  
 
For a faster rate decrease C31 and C32 and/or decrease R42. That's what sets the LFO frequency.  
 
For those without the schematic:  
 
You have an input buffer that distributes the signal to 3 paths: a "fundamental detector", the "distortion" circuitry and to the JFET that does the bypass.  
 
The fundamental detector is like what you find in an OC-2 octave down pedal. An active low pass filter followed by an "adaptive schimtt trigger" with rectifiers, comparators and a flip-flop - the net result is a square wave of the same frequency as the input. This goes to pin 14 of the PLL (signal in for the phase comparator). Pin 3 (the other phase comp input) comes from the VCO output (pin 4) frequency divided by 2 with a flip-flop. This way you have two outputs: at the same frequency of the note and an octave higher. The loop eror (phase comp output) from pin 13 is mixed to an LFO at pin 9 (VCO input). The two "feedbck tones" (following the note and octave higher) go to a simple anvelope generator like that used on the Blue Box, and after that there's the "overtone" knob that blends them. This goes to an active lowpass filter and then it goes to the distortion stage.  
 
The distortion stage input receives a mix of the signal from the input buffer with the synth'ed "feedback" tones. Then there's an opamp stage and diodes to ground followed by a typical distortion passive tone control and theoutput buffer.  
 
The DIY'er could do an "add-on" feedbacker for his favourite fuzz box with relative ease.  
 
The most interesting part of the circuit IMO is the switching circuitry. I still haven't figured out all of it.  

 
Replies:
JR Seeing as you seem to know the most... -- 11/18/1999 12:59 PM