Skull and Circuits ring modulator

Skull and Circuits has a maybe interesting new design:

This is a ring modulator with “added fluff”, which I guess is basically a built in oscillator / VCA to feed into the carrier and appears to account for at least 2/3 of the circuit. What interests me is the RM core which does use a diode ring, but does not use transformers. Instead op amps are used to inject the sum and difference of the inputs into the diodes and to act as a differential amplifier to get the signal out. I’d seen the idea alluded to here (I’m guessing that’s where S&C got it from) but that page doesn’t show an actual implementation.

A quick LTSpice simulation suggests this might actually be better behaved (less distortion) than the classical transformer design but don’t quote me on that. And op amps are cheaper than transformers. Not sure whether it has the same kind of bleed through tendencies the classical design has. My guess is it does. I’m putting this on my list of things to try breadboarding sometime (the core anyway, I’m not sure I’m much interested in the added fluff).

(Oh, also, that 100 nF cap in the output stage looks way too big to me. It makes a low pass filter but the RC frequency is only 1600 Hz, if I’m looking at it right.)


Added fluff is good. Fluffy strange stuff. It would be good if they sold PCB’s only as an option.