ARP Axxe: Voltage-Controlled LFO Speed

Analog Multiplier Method

A better way to do voltage-controlled LFO speed was pointed out to me by synth designer Skot Wiedmann...use an AD633 analog multiplier chip to control the amount of current flowing through the LFO circuit. I already had built the analog multiplier board for 5 AD633s, and adapting one of its slots for this pupose was pretty easy.

The LFOs square wave output voltage is multiplied by the Continuum's Y voltage and added to the voltage at the output of the speed control pot. The resulting voltage is sent to the 390K resistor and controls the amount and polarity of current flowing to/from the capacitor.

When the Continuum's "Y" output is 0 volts, the output sends only the voltage from the wiper of the speed control pot, just as in the original circuit.



(This schematic doesn't show the Fast LFO Mod)

The response of this circuit is nearly instantaneous; much faster than the photocell version. It allows rapid transitions between modulation frequencies.

Hear it: (coming soon!)