Ring Modulator with Low pass Filter and Filter Modulation

I have done some work to improve the basic Ring Modulator schematic of the previous post  to make it much cooler. I have added a 5 pole variable low pass filter with voltage controlled low frequency modulation. You can easily separate the sum and difference products at the output. With this you can get some incredible sounding low frequency drones and other effects. It also produces some very nice analog synth sounds. I am working on a layout of the prototype and may end up optimizing some values here and there. The breadboard version works well but there is a little modulation leakage at the high end. Hopefully a well grounded layout will solve this.

The design uses a TS922 op amp because it has great specs and is cheap  but others will work. I do not recommend the TL072 because the headroom is so bad at 9V.

The Demo Video shows me fiddling with the controls on the breadboard prototype and just noodling some random lines. It conveys just a few of the different sounds you can generate.

Schematic:

Demo Video:

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3 thoughts on “Ring Modulator with Low pass Filter and Filter Modulation

  1. Hi Rring! congratulations on the great design. I’m very excited about trying it myself. Do you know of any substitutes for the H11F1M optocoupler? Could a 4N28 or 4N35 be used instead?

    • Those opto-couplers are bipolar transistors on the output and may be able to be used but you would have to test it. In this application, the opto-coupler is acting like an analog switch. So you may just be able to use an analog switch – like a 4066 . Using a bipolar collector to emitter as an analog switch has not worked well for me when I have tried it.

      • ah! I didn’t realize you were using the square wave from the modulator. (Thought the optocoupler coulpler could be able to handle other waveforms).

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