DOD FX13 Gonkulator

The DOD FX13 "Gonkulator" is a MC1496 multiplier IC based ring modulator pedal.

This type of effect usually includes an internal sine wave generator to produce the classic "ring mod" sounds.

I'm always curious how the sine wave is generated, as it is not easy to generate a good sine wave.

The Gonkulator goes with a 2 op amp triangle wave generator (not shown) that is further processed by the above circuit snippet into a pseudo-sine wave.

Amazingly, the frequency of the internal oscillator is fixed! That may explain the lack of interest in this pedal. A sweepable oscillator is a must have feature for ring modulator effects.

I am curious if the wave shaping circuit above functions over a wide range, or if the R and C values were especially chosen for the fixed frequency. For voltage controlled sine wave generator, a function generator IC is typically used, which is practical, but somewhat boring, and those chips are expensive. (ICL8038 and XR2206 both produce sine waves and are found in "ring modulator" guitar effects.)