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Hey there guys,

I've been gathering some schematics for a ring modulator build. I've settled for an AD633 multiplier, and will also try the 4xOTA oscillator that Guillaume suggested.

I've also started to think about putting a LPF after the modulated signal - yes, this is becoming increasingly similar to Randy's Revenge - and there are some VCF schematics on the LM13700 datasheet. Have you guys experimented with these? I mean, I'm already going to use 2xLM13700 for the oscillator, might as well use 3 and have a filter too.

Following this thread, and because I'm building the said LM13700 sine wave oscillator mentioned previously, has anyone got a correct spice model for it? I've been running some simulations with Ltspice with a voltage-to-current source very similar to this one (http://www.birthofasynth.com/Thomas_Hen ... t_0001.pdf; I'm using +-9v and potentiometer is +9v to ground; R21 is 1M) feeding the Iabc pin. However I'm getting disparate results with the two models. In one, it works, and reacts from 10uA to 800uA on Q2 collector; in the other one, it only oscillates from 400uA upwards on Q2 collector. I still haven't tried it on the breadboard, and I don't have an oscilloscope to test it, so I have to rely on simulators.

One other thing, regarding square waves. This may sound stupid. Multiplying two signals (guitar*carrier), if I want on-off type of modulation (like a tremolo), the square wave needs to be 0-Vpeak, right? I mean, it needs to have a DC offset of Vpeak/2. Otherwise, if it doesn't, on the negative half of the wave, it will just invert the phase of the guitar signal, right?

Found these...

Beautifull board. Here I was thinking the filter was also LM13700-based. Guess not.

Vactrol is used for the filter, I guess. It has three 'legs' on the LDR side, so probably it's controlling R1 and R2 here?

That is a beautiful interior.

DWBH wrote:Beautifull board. Here I was thinking the filter was also LM13700-based. Guess not.

Vactrol is used for the filter, I guess. It has three 'legs' on the LDR side, so probably it's controlling R1 and R2 here?
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And why would it not be LM13700 based, I can see 2 of those on the pcb

Guillaume himself said that the oscillator used 4 OTAs (thus, two LM13700).