Adding Reverse Sweep Switch to MP Snow White Autowah?

[ItsGiusto]

Hey all. I'd like to build a Mad Professor Snow White Autowah clone:
http://tagboardeffects.blogspot.com/2013/04/mad-professor-snow-white-autowah.html
http://4.bp.blogspot.com/--dV3lzyt4Zw/T_xAYx1DuYI/AAAAAAAABuw/gfMLjzLKOV0/s1600/mpswaw.gif

I would like to add a "reverse sweep" switch to it, similar to the Mutron III's drive switch:
http://www.6v6power.ru/inf/Wah_AutoWah/MU-TRON%20III%20Auto-Wah.jpg

The problem is, I don't understand enough of the MPSW's funtionality, or the Mutron's to know how to do that. I have a feeling it would have to change something in the A2:A and A2:B area of the MP's schematic, but that's really just a guess. Does anyone know how I might include this mod in my build? Any suggestions on how to implement this functionality? Is it possible to do?

[duck_arse]

please don't quote me on this, but ..... if you removed A1:A from its current Vbias buffer function [and re/connect Vbias points], and wired it as an inverting amplifier (with a gain of -1) and then connected its input to the pin 7 of IC1, broke that connection and replaced it with the A1:A output, it would be the rectifier/sweep output inverted. it will sound different, would need to be tuned, but it seems plausible.

[edit :] don't ever " me, I looked again at the circuit tonight, and it is a little stranger than the usual rectifier setup. just ignore wot I rote.

[Mark Hammer]

Like I always do, I will mention here that getting a satisfying downward sweep is not simply a matter of electronically flipping things.  The start and end points of the sweep need to be adjusted from their defaults when sweeping upward.

Remember that the string itself "sweeps" from the moment you pick/pluck it.  It loses higher-frequency energy quickly, and settles down to mostly fundamental.  Sweeping "up" needs to be quick so that there is still harmonic content to emphasize by the time the filter gets there.  Sweeping "down" needs to be a bit slower so that you get to hear the dissipation of the natural harmonic content before the filter removes it.  So, it's not just the start and end points of upward vs downward sweeps, but also the speed at which those sweeps take place.  It could be added, but the stock SW does not include an Attack control.

[ItsGiusto]

Cool, thanks! Sounds more complicated than I hoped it was - maybe I'll forego the reverse switch for now. Maybe I'll try to build an actual Mutron III at some point in the future, once I get past my aversion to LDR builds.

[chemosis]

what about a lowpass mod like the dod 25fx has?? would it be the same mod for the swaw as the fx25???