Rackmounted remote wah

[bond]

Hey all,
Setting up my interface box for my rack, and thought I'd throw a remote wah circuit inside it,
I've patched together what I found in the anderson article and on RG's site, and made up a little remote wah schematic with the average mods on it:

http://img99.imageshack.us/img99/534/wahcircuitsz5.png

Are there any changes that should be made? (perhaps regarding switching the relay, I know they can make a very audible pop)

As I've got a crybaby shell, have most of the components on hand, and think I'll grab a fasel inductor off ebay, I'd like to iron out any errors before etching it..

cheers
bondy

[petemoore]

  Wah pot in a case and wah circuit in the rack...
  That means long way for signal from rack to treadle encased pot, back to Rack?
  And would tend possibly toward putting the Wah last in pedal chain?
  It looks like the 'cut-splice' marks by the wah pot are where...somehow [by use of jack?] the remote pot gets connected into the wah circuit.
  There are less 'surgey-noise' ways to do the switching than using relay, someone who's wired remote [4066 ?] can tell you more.
     

[Andre]

How about using a servo motor as used in model plains, boats and cars to rotate the wah pot in the rack.
The servo motor itself can be controlled by the pot in the wah shell.
You would need some extra electronics as the servo motor is controlled by a pulsewidth modulated 50hz squarewave.

André

[bond]

If you look at the schematic I've posted, the pot is optically isolated from the circuit, meaning the signal doesn't leave the rack ....

I guess the circuit is pretty much finished, I'm just paranoid about making a circuit board and finding I placed a wrong link or something ....

[DiamondDog]

If you look at the schematic I've posted, the pot is optically isolated from the circuit, meaning the signal doesn't leave the rack ....

I guess the circuit is pretty much finished, I'm just paranoid about making a circuit board and finding I placed a wrong link or something ....

Just looking quickly-

1M resistors across your cap selection switch would be a good idea to reduce popping. You might also like to include some resistors in series with the trim pots so you can't zero your resistance eg Q have 33K resistor + 50K trim pot.

I built a similar setup in a rig based on RGs pffootsw.pdf (40106/4013). All my fx are racked and left on, and taken out of circuit by this. Relays haven't presented a problem. As I am happy with the stability and longevity of the system, I'm also slowly redoing my stomps to suit- after all, I don't need switches or leds in the box any more!

The main differences between your setup and mine are the switch- I've built my treadle into the board, and use the switch from the above circuit. I also used a buffer on output, turning the trim pot into an external pot + resistors for some level adjustment. I also put a little trim pot in for led brightness adjustment in the LED/LDR combo, but I tend to overdo these things.

Hope that this is some help.

[bond]

cheers for the tips,
I'll definitely stick a trim in next to the led, and possibly a couple of trims elsewhere,
However don't think I'll bother with a larger resistor across the cap range switcher, I don't think I'll be fiddling with it to much ...

[trixdropd]

oops..wrong thread...

[R.G.]

Just to confuse things  () I've also made this work with a two uCs. The remote one reads the pot position from its A->D converter and sends that down the wires by its serial link. The back-home-in-the-rack uC receives the serial data indicating position, then sets the local pot one of several ways.

These can be:
- a digital pot; some of these are good, but you have to work hard to keep them from causing "zipper noise" because the resistor changes in discrete steps Take small steps and do something to "dither" the steps so they're at irregular intervals
- servo'ed LDR; uC puts out a voltage by PWM or other A-D method, then an analog circuit uses the voltage to servo a dual LDR so the slave/wah operating side follows the controlled side. Sounds like a pain, but works pretty well.
- PWM'd resistor
- switched-capacitor pot; both of these have to be watched because of sampling-time issues to avoid aliasing.
- mechanical servo/stepper motor; the uC drives a motor to turn a physical analog pot