Volume pedals, resistor-to-ground wahs and optocouplers: feeling really stupid

[David]

I don't get the amount of bench time I used to.  Simple stuff seems to be stretching out into YEARS.  Not to mention I'm further hampered by my lack of knowledge and experience...
Anyway, I have a perfectly serviceable volume pedal on my pedalboard.  But that's not enough.  I also want a wah, and I only want one pedal to fulfill both functions.  I have been doing a lot of research on this, and I am not satisfied with what I have come up with.

Where I am:
                        I believe I can implement a quite-functional volume pedal using a noninverting op-amp booster with a gain of 4 or so feeding a voltage divider consisting of a 1K or so resistor in series with the resistor half of an optocoupler connected to ground.  The volume pedal's output would be the point between the resistors.  The idea is the pot in the pedal is set up as a voltage divider between +9V and ground and rigged so the LED portion of the optocoupler gets dim as the pedal is rocked from heel-down to toe-down.  This increases the resistance of the optocoupler, pushes the voltage divider away from ground and toward the booster output.  The gain is to overcome the signal loss imposed by the small resistor needed to implement the voltage divider.

What I need to find out:
                          I want to also have a switchable setup between the volume pedal implementation described and a resistance-to-ground wah, like a twin-T circuit (the Coloursound inductorless comes to mind).  I would also like to implement the resisor part of this circuit with an optocoupler as well.  I know what the pedal does to a Vox-type inductor-based wah.  Can anyone tell me what the "average" response of a twin-T type is?  Do they usually go treble-y or bass-y as the pedal goes from heel down to toe down?  I need to know so I can figure out whether the behavior of my volume pedal would make the twin-T do what I want, which is to go from bassy to treble-y as I rock from heel down to toe down.

What I need to do:
                           If having the resistance of an optocoupler increase as the pedal goes from heel down to toe down does not make a twin-T type wah go from bassy to trebly, then how can I add a module to the circuit that I can feed a varying DC voltage that goes down as the pedal moves, but will make an LED go from dark to bright?  I tried to do this with an inverting op-amp buffer, but it behaved as if the LED was connected directly to the pot.  I would still also need the proper behavior for the volume pedal part of the circuit.

Note:  I envisioned switching this like a standard pedal, where a 3PDT switch selects the input, the output and which LED indicator to light.

[petemoore]

 For consideration:
  Buffer/split the input, feeding the wah always on side and a sidechain.
   A 3PDT should work if you put the 3 wah lugs on the 3 poles, one side connects wah as it was, the other side a boost or whatever [one or the other controlled by the switched pot]. A schematic helps to eliminate uneeded words like should.
  A simpler or less 'lug needy' switch wiring might also be possible, allowing a simpler switch or LED indicator.
 

[David]

I don't get the amount of bench time I used to.  Simple stuff seems to be stretching out into YEARS.  Not to mention I'm further hampered by my lack of knowledge and experience...
Anyway, I have a perfectly serviceable volume pedal on my pedalboard.  But that's not enough.  I also want a wah, and I only want one pedal to fulfill both functions.  I have been doing a lot of research on this, and I am not satisfied with what I have come up with.

Where I am:
                        I believe I can implement a quite-functional volume pedal using a noninverting op-amp booster with a gain of 4 or so feeding a voltage divider consisting of a 1K or so resistor in series with the resistor half of an optocoupler connected to ground.  The volume pedal's output would be the point between the resistors.  The idea is the pot in the pedal is set up as a voltage divider between +9V and ground and rigged so the LED portion of the optocoupler gets dim as the pedal is rocked from heel-down to toe-down.  This increases the resistance of the optocoupler, pushes the voltage divider away from ground and toward the booster output.  The gain is to overcome the signal loss imposed by the small resistor needed to implement the voltage divider.

What I need to find out:
                          I want to also have a switchable setup between the volume pedal implementation described and a resistance-to-ground wah, like a twin-T circuit (the Coloursound inductorless comes to mind).  I would also like to implement the resisor part of this circuit with an optocoupler as well.  I know what the pedal does to a Vox-type inductor-based wah.  Can anyone tell me what the "average" response of a twin-T type is?  Do they usually go treble-y or bass-y as the pedal goes from heel down to toe down?  I need to know so I can figure out whether the behavior of my volume pedal would make the twin-T do what I want, which is to go from bassy to treble-y as I rock from heel down to toe down.

What I need to do:
                           If having the resistance of an optocoupler increase as the pedal goes from heel down to toe down does not make a twin-T type wah go from bassy to trebly, then how can I add a module to the circuit that I can feed a varying DC voltage that goes down as the pedal moves, but will make an LED go from dark to bright?  I tried to do this with an inverting op-amp buffer, but it behaved as if the LED was connected directly to the pot.  I would still also need the proper behavior for the volume pedal part of the circuit.

Note:  I envisioned switching this like a standard pedal, where a 3PDT switch selects the input, the output and which LED indicator to light.

I see I did my usual STERLING job of explaining myself.  OK.  I stated the part about the volume pedal to indicate that the design parameter, if you will, was that the desired behavior was to make the desired action happen as the pedal went from heel-down to toe-down -- ergo, volume would increase or wah would go toward trebly.  Of course, the wah would also have to go bassy as the pedal moved from toe-down to heel-down, but I hope that would be understood.  I only brought up the switching to indicate that I wanted to switch between volume and wah modes and use only the one pedal.  The way I planned to implement it was to make the LED in an optocoupler go dark as I moved the pedal from heel-down to toe-down to increase volume as I tried to explain above.  I would hope I could implement that without too much trouble.

Where I really blew it seems to be the stuff about the wah.  The first thing I'm trying to find out is, on a resistor-to-ground wah (for example the Coloursound inductorless), does increasing the resistance to ground make the wah go trebly or bassy?  If that makes it go trebly, this is the same behavior as I expect in the volume pedal.  If, however, increasing resistance makes the wah go bassy, then I need a way to make the LED part of the optocoupler go brighter as the input voltage decreases.  I thought about using the PNP portion of the 3-pole Rock'n'Control, but I couldn't tell if it could just be pulled out and function on its own.

And yes, I could try these out on my own,  and ultimately will.  With limited bench time, I would like to limit the number of bunny trails I have to follow, if you know what I mean.

[petemoore]

  The only thing LDR's have failed to do for me [that mattered] is to go really low ohmage, two in parallel LDR's = reducing the R value down nearly another 1/2 of what the 'low reader LDR' would read in lit condition.
   They can go really high R value anyway, or use two in series and make it a meg+ high R value.
   A parallel, fixed stop resistor [across the LDR] can be used to set a on limit the Max-Dark resistance..
   The rockin' control [iirc] is a ''photocells-circuit = volume pot replacement''. Volume pot is basically the same thing as a wah pot, sometimes a different taper.
   

[David]

The schematic for the Morley PWV from the late 90s would indicate that the resistance of the volume LDR increases as the pedal moves from heel down to toe down.  This is connected directly to ground.  It has to be a simple rheostat with increasing resistance to increase volume.  Assuming the shade mechanism for the wah LDR moves in the same direction, the wah LDR could be expected to increase in resistance also.

I will breadboard the PWV and find out.