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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

Re: Super Feedbacker

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.

11/19/1997 9:43 AM

Mark Hammer
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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.

Replies:

Adam Frankowski > I'll see if I can do a quick clea... -- 11/19/1997 2:01 PM