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|previous: Mark Hammer I'll see if I can pop the lid off a... -- 10/31/1997 2:03 PM||View Thread|
|11/19/1997 9:43 AM|
|Mark Hammer||Re: Super Feedbacker|
Somebody sent me a scan of the BOSS schematic for the Feedbacker (sorry, I forgot to write your name down before I came to work. Is it David Rusk? Thanks anyways; I'll get the name right next posting).
As suggested by others, the DF-2 *does* use a a primitive pitch-extractor, feeding a phase-locked loop (a 4046), whose output goes to a flip-flop. The output of the flipflop is nicely low-pass filtered, and a pan control adjusts how much of the two overtones gets shunted to ground.
The overtones get fed to a standard back-to-back diode pair clipping circuit (following an adjustable gain stage a-la-MXR Dist+) in tandem with the normal signal, then through a Big Muff-style tone control (pan between single-pole HP and LP filters) and then off to the master output volume.
The switching scheme applies an envelope voltage to the collectors of a pair of transistors taking the overtone feed from the flip-flops whenever the footswitch is held down. A simple RC rise-fall time setup brings the overtones in and out smoothly, effectively gating them out of circuit when the switch is released.
Reasonable areas for mods include:
- taking out some of the LP filtering in the overtone section to make it "ruder"
- tweaking the pitch extractor filtering or component matching to get accurate pitch extraction
- playing with the 4046 PLL to get a different series of overtones
- tweaking the cap values in the tone section to get a broader palette.
I'll see if I can do a quick cleanup of the scan over the next few days and turn it into a compact 1-bit GIF for those interested. Right now its in two large JPEG's.
|Adam Frankowski > I'll see if I can do a quick clea... -- 11/19/1997 2:01 PM|