1631 Ring Modulator

AM1631 Artwork

Introduction In August 2020 I bought a set of Behringer System 55 modules, as my first journey into Moog modular. My plan is to recreate the Klaus Schulze IIIP synthesizer and Dual Sequencer setup that Klaus bought on 22nd December 1975, and used successfully for many years.

Whilst the Behringer modules cover most of the Moog modules I need, there are a few additional modules and changes I have made. One of the biggest gaps is a Ring Modulator.

AMSynths 1631 Ring Modulator This is a replica of the module that Bob Moog built for Keith Emerson sometime in the 1970’s, which was based on the circuits in the Bode Frequency Shifter.

The original Bode circuit has two multipliers, one based on the UA796 and the other based on the MC1494. The UA796 is possibly the first dedicated modulator chip manufactured from 1973 by Fairchild Semiconductor. Ring modulation became a popular effect in the 1970’s and it was championed by ARP in their synths rather than by Moog. Roland picked up on the idea in both the System 700 and 100M modular synths. Klaus will have used his ARP 2600 for ring modulation sounds, and then perhaps the PPG 300 which has a rather nice Dual Analog Multiplier.

I have designed a UA796 based circuit taking inspiration from the Bode frequency shifter and the Roland 700 Modular. I have a small number of UA796 chips in stock and the circuit also uses a LM301 Op Amp, both are in vintage TO can format.

The circuit is sufficiently simple to fit two Ring Modulators on a small 8HP wide PCB and it includes a modulation level pot and a green front panel LED which indicates the output level.

I put together a prototype in October 2020 and with a few modifications it worked very well.

Outcomes The AMSynths prototype PCB was tested in October and it works well, with some minor corrections which resulted in a revision of the MAIN PCB. An initial set of panels were ordered but needed corrections.

Copyright AMSynths 2019