Ring modulator from 2 VCAs?

[spasticteapot]

From what I understand, it should be possible to build a ring modulator using two VCAs and a clever use of diode. The carrier frequency would be fed into the inputs of both VCAs, with the outputs wired in parallel, but with opposite polarity on the input. By using "ideal diodes", the positive half of the audio input signal would be sent to the amplitude modulation of the first VCA, and the negative half to the second VCA.

If I understand ring modulators correctly, the net result should be roughly the same - the phase and amplitude of the carrier frequency would be modulated by the input frequency. Would this work? CA3080Es are a lot cheaper than AD633s.

[soggybag]

I think you can build a Ring Mod from one 3080 and a couple op-amps. Use two op-amps for an oscillator. Oscillator is connected to the pin that controls level of the output (I forget what it's called). I could post a couple schematics.

[PRR]

There's 2-quadrant VCAs and 4-quadrant VCAs.

4-quadrant operation is shown in Fig 1 of the MC1495 datasheet. Link

2-quadrant won't go through zero and invert, which is fine for things like volume controls which must stop at zero.

You are correct that two 2-quadrant VCAs with (possibly) a perfect diode re-combiner make a 4-quad VCA which can be applied as a "true" ring modulator.

But imperfections (between VCAs or in diodes) will give a MAJOR glitch in the sound at small levels. "Ideal" diode schemes lessen the glitch, but don't remove it.

For musical effects you don't need a highly precise (multiplier quality) 4-quad VCA, but you do want no-glitch sound. So I would stick with the various 4-quad multipliers, such as the venerable MC1495, even the cheezy ones like four plain diodes in a ring between transformers. And AFAIK, 30+ years of designers have pretty well mined the bottom of this bucket.

And a simple 2-quad multiplier (CA3080, 6BE6, Fender bias tremolo) gives an audible effect not quite like a ring modulator, but equally useful for most "effects" purposes, and so much easier.

[spasticteapot]

I suppose your right.

I found a place that sells AD633s at a reasonable price, so maybe I'll try giving one of the traditional schematics a shot.

[Lurco]

page 11 figure 6.  http://www.national.com/ds/LM/LM13700.pdf

[StephenGiles]

Find out how Jeff Beck achieves the effect with just his fingers!