Steiner-Parker VCF simulated

I spent Friday night at my internet-less grandparents, but I still got some work done on simulating some schematics I already had laying around.

I saw this schematic for a filter inspired by the one from the Steiner-Parker Synthacon, and was taken by both its simplicity and its unique design. I haven’t really done a lot of analysis of it, other than that it uses a string of eight diodes as voltage-dependent-resistors to vary the cutoff frequency.

Unlike many multimode filters, each mode has its own input but the filter has a single output. Most filter modules you regularly see have a shared input for each mode, but with separate outputs. This one looks the most similar to a filter topology I’ve seen in school, the SAB or single-amplifier-biquad, but I haven’t really given it an in-depth look.

Anyway, the schematic can be found here. Props to Ken Stone for his work. I might buy some of his PCBs sometime.

I made a crappy sawtooth oscillator (perhaps a post on that later) and then loaded Ken’s schematic into LTSpice, then fed the oscillator output into the filter’s low-pass input. I set up a piece-wise-linear voltage source to drive the oscillator with an eight-step sequence and summed three slow triangle-wave voltage sources to drive the filter’s cutoff. I hard-set the resonance to max–in my simulation this didn’t cause oscillation as Ken’s website noted. *shrug*


Here’s the 64 seconds of synth-filter sound that I coaxed LTSpice into dumping out:

This filter’s squelchy goodness is really remarkable. When I ever get around to buying some CGS PCBs these will definitely be on the list.


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One Response to “Steiner-Parker VCF simulated”

  1. thecuriousbum Says:

    60s-70s SciFi!

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