Moog Music Forum

Maybe this is taking analogue too far but I'd really like to be able to control both the cut-off and resonance using analog controls. I know I could plug an expression pedal into the cut-off cv, but I was wondering if anyone knew of a product that did the same thing except it is a knob instead of pedal.

Thanks for the input. I do have a Korg keyboard which has assignable midi knobs, but I was looking for straight analog. I'll keep looking.

Expression pedals are essentially just plastic or metal housings around a potentiometer.

You could just take the guts of an Expression pedal, put them in a little box, and put a Radio Shack knob on top of the pot.

Sorry - I see Dada already pointed out the Expression pedal mechanics.

The good thing about the Expression pedal is that by using the TRS plug it's drawing the voltage from the synthesizer, where if you make your own circuit you'll most likely have to supply a battery for CV.

The old Moog and Korg CV pedals required a 9V battery. New Expression pedals use a TRS plug to get around that.

I use M-Audio Keystation Pro 88 and set up all the knobs there is 24 of the on the Pro 88. It works great.

Just use an expression pedal connected to the "filter CV" input jack on the LP to control filter cutoff, and use the Filter section RAC knob to control Resonance. Voila; all-analog control.

As has been said, you can wire up a knob and potentiometer to work just like the expression pedal. You'd need a TRS plug with the sleeve contact wired to the counterclockwise leg of the potentiometer, the Ring contact wired to the clockwise leg of the pot, and the tip contact wired to the center (wiper) leg of the pot. That will create a 0 to +5V voltage divider, exactly as in the expression pedal. I recommend using a 100K Ohm linear pot.

Amos wrote:Just use an expression pedal connected to the "filter CV" input jack on the LP to control filter cutoff, and use the Filter section RAC knob to control Resonance. Voila; all-analog control.

As has been said, you can wire up a knob and potentiometer to work just like the expression pedal. You'd need a TRS plug with the sleeve contact wired to the counterclockwise leg of the potentiometer, the Ring contact wired to the clockwise leg of the pot, and the tip contact wired to the center (wiper) leg of the pot. That will create a 0 to +5V voltage divider, exactly as in the expression pedal. I recommend using a 100K Ohm linear pot.

That was exactly what I was looking for. Many thanks Amos. I don't have a lot of experience soldering, but I do think I can manage a project like this. Excellent!

Pot Mapping?

-detune-

Well, I got a 100k pot, wired it up and it works. Unfortunately, it only chages the cutoff on half of the full range. If I have the cutoff on the LP all the way down, my outboard knob will only bring the cutoff halfway up. I need to put the LP knob halfway for my outboard knob to take the cutoff up all the way, but then of course, it will only go down to halfway. Is there a different resistance pot that would cover the full range of the cutoff?

try a 50K? Also, use a voltmeter to be sure the pot output is really going from 0 to 5v.