how could you get that boo-wah sound from a momentary switch?

[mikemaddux]

I know that this isn't anything new, speedy west used one of these mounted on his steel guitar back in the 50's....

How would I wire a "boowah" sound from a momentary switch?

This is the sound from a wah pedal, or from turning your tone control all the way down then all the way back up immediately.

Fender and a few different companies put left to right controls on some of their volume pedals to give you this "boowah" sound.

My question is:  If I were to wire a momentary switch, would I wire it to a cap? what size?

the idea is when you press the switch the highs are cut, and it comes back when the switch is off. 

What really trips me up is how do I get it to "ramp" up and down?

[GibsonGM]

Sounds like a filter to me, man.  Coming off the switch you'd have a resistor with a cap to ground, the output coming from where they meet (LPF).   Playing with values will determine your cutoff frequency (Fco), or how "bassy" the filter acts as it dumps the highs to ground.   The formula for that is Fco=1/2piRC....reduces to 1/6.28*RinOhms*CinFarads.  The number you get represents the -3dB point, or where the signal is 1/2 as loud as the input.

The same formula is used for high pass filtering, BTW.

As far as moving that frequency around like the old-style wahs, you'd need to alter the value of resistance.  Doing this on a momentary switch doesn't seem very easy to me.

[Paul Perry (Frostwave)]

The only way I can see to actually move the filter freq over a period using a momentary switch, is to use the switch to charge/discharge a cap through a resistor & use the rising/falling voltage on the cap to control a voltage controlled filter.

Easiest way to adapt an existing circuit, would be to have a wah type circuit with a LDR as the wah resistor.
Then arrange the switch & resistor & cap to give the varying voltage & feed the controlling voltage to  a buffer and then use the buffered voltage to control a LED which in turn controls the LDR (vactrol). Some experimenting to get the setup tweaked right - but the theory is straightforward.

If I was doing it myself, I'd be using a voltage controlled filter based around the LM13700, but that's just me..

[RickL]

Try building a Morley Pic-A-Wah using a momentary switch in place of the metal pick. A switch will perform exactly the same function as the pick, grounding a point in the circuit to trigger the filter. This is essentially Paul's idea.

Look for an earlier post by me for a review of the circuit.

[mikemaddux]

Thanks guys, Im gonna try to get the wah circuit built soon to get the right sounds.

But I built it tonight, with a momentary switch connecting to a cap and a LDR. 

I step on the pedal and the cap cuts the treble.
No ramp but ill work on that. 

I put a on/off switch in that connects to a flashing LED that gives me a tremolo effect, and another on/off switch that turns on a non-flashing LED with a momentary switch connected so I can boost the output of the treble-bled signal. 

Nice....