"Foxy Jailbait" - FX-17 Wah Clone for a Standard Shell

[Earthscum]

Thanks, first of all, to Jimi Photon for the suggestion to "clone" this pedal. Secondly, Thanks a TON, Paul Marossy, for the schem.

Here's where you can find info about the original FX-17, courtesy of Paul: http://www.diyguitarist.com/DIYStompboxes/FX-17.htm (at the bottom is a link for the schem, but I should have all the parts for this posted up here).

What I've done so far is brain work and probing, poking, and prodding.
What I've been able to do is get the CV working from a pot, in trade for the PCB footprint that the CD4007 took up. Win-win! 100k Linear pot, no tapers to mess with (it messes with the CV).
I've also eliminated the DOD switching in lieu of a DPDT. This takes out another CD4007, 4 resistors, and a cap.

And, finally, a mod to go to LP or BP.

[Ronan]

Nice work. Would it be possible to also eliminate the J113 switching circuit and use true bypass? The buffer could be hard-wired to the VCA and VCF and a SPDT toggle switch could be used to select the output for wah or vol mode (and another SPDT for LP/BP). I'm hoping to breadboard the wah part tomorrow with an LM13700. I love this sound clip of an original, about 1:30 onwards.
http://www.youtube.com/watch?v=IashsPtlsL0

Just wondering if the control voltage derived from the pot couldn't be put through a lower parts count circuit to give the required result? I'm not a designer by any means, but could trimpots be used either side of the variable 100K pot to limit the range, and simply eliminate the LM358 circuit, driving the 1N914 and D2 green LED straight from the transistor buffer circuit?

[Earthscum]

Yeah, you can true bypass it like any old Ibanez or Boss (or DOD). But, why? Ya want a TB wah pedal, a Crybaby would be much easier to deal with. Seems to me kinda like spending half an hour combing your hair just to plaster a beanie over it. Case Against True Bypass

Also, the 358 provides a bit of protection for the OTA's, buffering the wah pot (and getting rid of the scratchiness). Basically what you are asking if can be done is "Can I make Escebedo's Sallon Key Filter". Sure, go for it... lits of threads here about it.  It's similar to how you essemtially have a Dist+ if you take out the buffers and tonestack from a DS-1 circuit.

Tech info:

This provides 5V CV output in any mode, on or off. In VOL mode, it doesn't switch on or off...it's a straight volume. In Wah mode, it switches the wah on or off.

Tuning this is a bit weird. Trimpot P2 controls how wide the sweep is, and Trimpot P1 centers the sweep. If you take measurement with a DMM at the 5V CV out, you can adjust these. I used a scope, but essentially you can do this with a DMM. I started with P2 full resistance, center the wah, and adjust P1 to 2.5V, then rock all the way down and make sure it's at 0V and moves up from there. Took me a couple times going back and forth, but once it's set, you're good.

[Ronan]

Basically what you are asking if can be done is "Can I make Escebedo's Sallon Key Filter". Sure, go for it... lits of threads here about it. 

Splendid idea! Thanks, I'll do that.

[Earthscum]

Actually, since it's completely relevant, there's another thread going on about the MS-20 filter: http://www.diystompboxes.com/smfforum/index.php?topic=97062.0

And a link from that thread to Tim Stinchcombe's analysis of the Korg, MS-10, and MS-20 and various topologies based around the Korg filters: http://www.timstinchcombe.co.uk/index.php?pge=korg

Since all I have at the moment is a SMD LM13700 (mis-order), I was pondering using the CV portion to drive other filters and what not. The other half of the 358 could be set up as a buffered voltage reference, and it could easily be a stand-alone unit that you could use as a daughter board and build build off of.