CA-9 Ring Modulator as a 9700 Series Module

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CA-9 Ring Modulator as a 9700 Series Module

Post by PAiA-Scott »

A year ago I purchased a 9700 basic setup (i.e. 9700 MIDI-CV, 9720 VCP, 9730VCF, and 9710 VCA.) I have just started to expand the setup with other modules.

One thing that I always wanted and is part of my intended upgrade is a ring modulator. I have decided to use the CA-9 as a base.

I will keep everyone informed as to how it goes, but before I get much further into it, does anyone have any suggestions to make it easier to integrate into the 9700 series. The obvious things such as knobs, and 1/8 inch jacks, as well as replacing the slide switch with the 9700 style toggle switches are so obvious that I made those purchases even before starting the kit. But there are still the other less obvious ones. For instance I get the feeling that the CA-9 is intended to work primarily with guitar level signals which appear to average about -10dB to -20 dB while the 9700 seems to run a bit hot at about +5dB to +10dB. Furthermore are there any issues involved in tying the CA-9 into the unregulated +/- 18 volt 9770-u.

In general, is there anything that I should be aware of that I am not even thinking about?


David Courtney

Hello David.

A similar function is available by connecting multiple VCO waves through the Triple VCA/Modulator. Connect one wave to the VCA A input and the other wave to the VCA A Modulation input. This provides a balanced modulator effect which a ring modulator provides, and the CA-9 project mimics. It's extra harmonics added to the input signal for a 'de-tuned' short wave radio sort of sound good for complex tones or robot-like voices.

To use a CA-9 project in a FR-7 chassis powered by the 9770U, you'll need to drill holes to mount the printed-circuit-board to a FRB panel and for the controls, switch (sub'ing a toggle switch for the slide switch), and connectors. Then, for adapting it to the +and- 18v supplies, add a couple of 9.1v zener diodes in parallel with the Cs 7 and 9 power supply input filter capacitors (the banded cathode ends to match the plus poles of these electrolytic capacitors).

Use the 330k resistor for R12 as suggested for line-level use, and either attenuate the waves input to the CA-9 by running through VCA L and/or VCA R and using the L+R output (half of the maximum input to L or R, but also variable by the Pan setting), or, substitute a lower valued resistor for R17 (a 47k makes IC1A work with 0.5x gain).
Scott Lee