Wah Wah optocoupler

[spoontex]

Hi,

I want to build a new wah, because all the wah's that I have, over the time the pot scratches and honestly doesn't sweep very well. The idea is that put the circuit into a Hammond 1590BS, wich is 4mm taller.

This are the requirements:

Adjustable parameters via trimmers.
Output buffer
Volume pot ( panel )
Rotary switch ( different cap values )
Controllable sweep with panel mount pot ( static ) and via external expression pedal.

I draw the schematic and the layout.

Anybody can tell me If avoid something or I made some mistake?

Thanks.

https://i.ibb.co/7ynWM3c/schem.png

https://i.ibb.co/SJNpwKs/3d.png

https://i.ibb.co/kGFk2qc/layout.png

https://i.ibb.co/nRRmfs1/pcb.png

[anotherjim]

Do you have a schematic of the original pedal wah?
The LED in the optocoupler has a forward voltage - it will go dark before the pot sweep gets to zero.
The dark resistance of the coupler might be too high to get a good sweep from the pot.

[spoontex]

The schematic is the basic wah circuit.

Forward voltage, may be adding a electrolytic cap into the pins 1 and 3 of the pot?

[spoontex]

The NSL-32:

Silonex NSL-32, photocoupler with 4 leads. If of the LED is 40mA, der at If=20mA Ron=500 Ohm, Roff=500kOhm.

The dark resistance is too high?

[StephenGiles]

The good thing about using an opto is that you can bias the voltage however you like and therefore adjust the pedal sweep to match the pot law.

[spoontex]

Yes,

I think about that.

Maybe a 500R resistor in series with 2k trimmer?

[anotherjim]

So it's a standard CryBaby
I'm sure this has been dealt with before. Long ago.
http://www.geofex.com/Article_Folders/wahpedl/wahped.htm#ryo
So it looks like you've done the same as the Anderton remote pot mod. It should work.
You can lower the LDR dark resistance by putting a resistor in parallel with it. 1M maybe but you may not need to.

[spoontex]

Exactly,

I saw it in an old magazine, which I found online.

The voltage control with jfet looks interesting. Anybody know if this method has some time lag on the response? or anybody tried?

Thanks.

[antonis]

The voltage control with jfet looks interesting. Anybody know if this method has some time lag on the response? or anybody tried?

No time lag..
(at least, not longer than LDR response..)

[iainpunk]

Jfet CV is about 28000x faster than LDR's so i don't think its a problem (LDR's mostly stop at 500Hz, where the BF245 goes up to 14MHz)

[spoontex]

Thanks,

I will try it.