The Forbidden Resonator

If you have looked at some of my other devices (especially The Exalted Birds) it is readily apparent that flouting conventions and orthodoxies is a running theme in my work. When the lofty & exalted chief-designers of integrated circuits hand down their blueprints to the factory. These designs are usually biased to a specific application. For instance, an op-amp is a very standard chip, but there are hundreds of different op-amps; all with different advantageous attributes designed-in. One type might be designed to perform well while using very little power-supply current, while another might hog that current, but it performs perfectly at very high speeds. Whenever one attribute is emphasized, it is always at the expense of others and these ‘flaws’ sometimes yield unanticipated behaviors under particular operating conditions. Some very creative designers have exploited these accidental ‘features’ to use these chips in applications for which they were never intended. There is (at least for me) a tremendous romance to this concept. Some great examples of this practice are the ‘Swash‘ circuit by the formidable Dan Green of 4MS modules. The CMOS-abusing design of the VCF in the EDP Wasp, and even (some might argue) the outrageous & prolific exploitation of the many quirks of the LM3900 Norton-amp that Serge Tcherepnin deployed in the majority of the original Serge module designs.

I just love that kind of stuff. Using a device in a way that flouts the conventional intentions of a commercial designer has the thrill of heresy for me. The resonator circuit in this box is one such heresy. It’s circuit topology is ‘wrong’. It is not an idea that is wholly original to me (and for that reason I’m not comfortable publishing schematics) but the implementation of the exploited ‘flaw’ required a huge quantity of trial and error to find modifications that yielded it’s trick stably & reliably… and with voltage controllable parameters. Those CV parameters are always crucial to me.

The core circuit is essentially a resonator that adds and emphasizes harmonics. The frequency ‘center’ of the added harmonics is voltage controllable, and the phase of the harmonics is also moved by a control voltage. The amplitude of the input signal has a non-linear effect on the number of harmonics produced so there is a manual control for that parameter. The sound is especially rich and animated when the input signal is low frequency. This circuit is clearly a processing MODULE. But I decided to implement it in a standalone form with an onboard pulse-wave VCO and a complex smooth random generator for each voltage controllable parameter. So the device can be used as a standalone voice in performance as well as a processor.

The Resonator controls themselves are in the vertical ‘body’ of the box. The control voltage generators and VCO controls are in the horizontal deck mounted on the lid.

The box was a gift from Dave Vosh, an old friend and a very gifted synthesist. He knows about my admiration for the Bebe & Louis Barron soundtrack for ‘Forbidden Planet’ and the ‘Forbidden’ technology aspect of this heretical design was just too tempting to pass-up.