Rambler, Penny Pedals Fingerprint etc

[jishnudg]

http://revolutiondeux.blogspot.com/2012/01/penny-pedals-fingerprint.html
http://www.deviever.com/fx/tim/


Just wanted to understand the theory behind these circuits. Both use LM386 audio amplifier chips, but the way the diodes are producing octave tones seem to be different. The Fingerprint connects the diode between the output and input with a pot in between. Tim's design has a schottky between the inverting and the non-inverting input.
So how do these circuits work, electronically I mean? Am just trying to understand the nuts and bolts of the 386 chip....also, are there any other designs that use the 386 in unconventional, innovative ways?
Thanks,
J.

[jymaze]

In my opinion it has everything to do with the diodes and not much to do with any particular functional attribute of the LM386. Functionally, it could just be any opamp there (may need some tweaking, but same function). I guess the LM386 is chosen because of its power handling which comes in handy when driving diodes to ground without current  limiting resistor.

[jishnudg]

Hmm...that makes sense...but what exactly is the diode doing there and is there any way to configure it to act optimally..?..I'm just guessing that the diode is working similar to how the feedback diode works in the ROG Bazz Fuss  (http://www.diystompboxes.com/smfforum/index.php?topic=80293.0) in producing the fuzz and octave up tones.

[slacker]

The Rambler uses the diodes to split the input into its positive and negative parts. The positive part of the wave goes into into the non inverting input so comes out the same way up, the negative part goes into the inverting input so comes out inverted, so it's the same way up as the positive part, so the output is a rectified version of the input  at twice the input frequency.

The footprint feeds back some of the output signal to the input, the diode blocks the negative part of the output, which as it's inverting is the positive part of the input. I guess at certain settings this will sound a bit like an octave up.