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Old 06-24-2011, 09:05 AM
Dan Dan is offline
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Join Date: Jun 2011
Location: Czech Republic
Posts: 5
Smile MPA as WAH or AUDIO pot

Hi, i have made MPA module for controlling 100k Wah pot in Cry Baby.
It makes "- some sort of artifact from the "steps" in the digital pots- ".
It makes the wah unusable.
The Mpa pot replaces the wah pot, I must say, no kind of shielding helps to remove digital artifacts.
It is probably dependent on the use in the audio circuit, in Dunlop's Cry Baby the MPA cannot be used.

It can be resolved by using optocouplers. Schematics in attached picture.
I found Silonex NSL-32SR2 to be well suited, as they are quite fast and have low current response to make it possible to use direct with MPA.

Using one OC :
it is implementation of "wah pedal retrofit from Anderton" . 5k6 resistor is here to prevent wiper current higher than 1mA in MPAs wiper position near to "5V" pot output. Wiring with MPA is in Fig.1.
It has sharp change of value in middle position of pedal. It is due to nonlinearity of OC. See fig.3.
Someone can like it.

I am personally using two OCs. See Fig.2
Two MPAs pots go together (the same controller), wired opposite make from two OCs one pot. It does not matter, whether 10,50 or 100k MPA, it is only voltage divider for OCs.
P1 pots can be used to modify OCs behaviour, P2 pots make resulting output resistance and can slightly affect middle position of "wiper".

This new pot is not linear but usable. It is the way how to make pot with higher resistance then MPAs 100k. (In this case may be better NSR3)

The new pot can make wah sound different , as it can change LC circuit in wah pedal. Some mods can be useful to make wah sounding to your taste.
Good mods explanation is here :
and here :

Negatives :
The speed of OC is not very high, the "speedy tremolo sounds" are not possible. For usual tempo tapping is it OK.
I will try Silonex NSL-32SR3, as they should be faster with higher resistance.

Finally I have the midi wah pedal.

By the way, the customer support of Highly liquid is :


Last edited by Dan; 10-10-2011 at 01:54 PM.
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Old 07-03-2011, 06:34 AM
Dan Dan is offline
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Join Date: Jun 2011
Location: Czech Republic
Posts: 5
Default Silonex NSL-32SR3

I have now tried Silonex NSL-32SR3 and they are faster and with higher resistance. It needs more tweaking with supply current to have a good result. Finally I decreased the value of "sweet cap 10n" to 1/2 in the wah circuit.
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Old 08-29-2011, 07:02 AM
alsercol alsercol is offline
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Join Date: May 2011
Posts: 11

Sorry, but I can't see the schematic. Would you post a more resolution image? Thanks!
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Old 09-05-2011, 08:57 AM
Dan Dan is offline
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Join Date: Jun 2011
Location: Czech Republic
Posts: 5
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Or this.. Must watch, what I have sent
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