Ring Modulator Module for Modular Synthesizers

Ring modulation takes two signals (called "carrier" and "modulator") and produces the sums and differences of the frequencies on the carrier and modulator signals at the output. Ring modulation in music is one of those audio frequency shaping effects that charms advanced musicians more, immediately after the filter, someone could claim.

A ring modulator opens a whole lot of sonic capabilities to a synthesizer, and can give satisfactions especially if you are hunting for sci-fi and special effects. This makes it a nice tool to add to our noise making arsenal.

In this instructable I will show you how to realize a simple-but-effective ring modulator module built around a single chip: the Analog Devices AD633.

I will share with you Gerber files of both main board and panel board (face plate) so that you can have them manufactured at the best price around and speed up the realization of the whole module consistently.

Let's go then!

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The circuit adopted for this module is built around a single chip: a four quadrant, analog multiplier called AD633.

Although not as cheap as the datasheet would like to imply, this IC stimulated the imagination of a whole lot of tinkerers at the point that a lot of different circuits where proposed online in the past.

The one here is very similar to the one firstly proposed by Roman Sowa in the first years of 2000 (LINK), and then used by a whole lot of people with minor to no modifications. Take a look at Roman's Blog: you will find other circuits and modules he developed to take inspiration from.

Back to the Ring Modulator, the barebone circuit is very simple and uses a minimum amount of components: some resistor, a couple of capacitors and a quad op-amp (TL074)... and obviously the AD633.

The operation principle can be described as follows: buffered modulator and carrier signals enter the "magic" integrated circuit. Part of the buffered modulator signal is halved in intensity and passed downstream the AD633, then blended with the modulated signal via a potentiometer. This potentiometer controls the amount of "dry" signal with respect to the "wet" signal. The derived wet/dry signal is then passed to the last stage of an op-amp for a fixed amplification (X2 gain).

Upstream the circuit there are two capacitors for AC/DC coupling. They come of essential use if your carrier signal is not AC (it should be) and leave to the musician the choice on the modulator signal coupling.

The module I have layed down provide two 1/4" jacks connectors where to feed carrier and modulator signals, with control over intensity via two potentiometers in voltage divider configuration.

The relative intensity of dry (modulator) and wet (amplitude modulated carrier) signals can be tuned via the dedicated WET/DRY potentiometer.

The PCB board is intended to be mounted perpendicular to the face plate aluminum board.

Gerber files of both PCB's are stored HERE (Github). You can have them manufactured HERE (JLCPCB, affiliated).

Disclaimer: I often confuse carrier and modulator. It makes more sense to me to think at the first as the main signal source and the other to the modulating wave, but looks like it's not the case. My prototipe (the one pictured in this instructable) was reversed. Even if it's only a matter of labelling, this issue is fixed in the shared files.

Please notice that face plate holes are dimensioned for 1/4" jack connectors, not eurorack standard 1/8" connectors. You can eventually download blank faceplate files at THIS link (Github). Included are boards source files (.brd) so that you can laydown appropriately dimensioned holes and silkscreens where you prefer, as a function of your module idea.

Here is the bill of materials:

Resistors and Potentiometers

• 1x 10K ohm potentiometer
• 2x 100K ohm potentiometer
• 1x 1K ohm resistor
• 2x 1M ohm resistor
• 2x 6.2K ohm resistor
• 2x 15K ohm resistor
• 2x 30K ohm resistor

Capacitors

• 4x 100nF ceramic capactors
• 2x 4.7uF electrolitic capacitor
• 2x 10uF electrolitic capacitor

Diodes and IC's

• 1x TL072 Op-Amp
• 1x Ad633 analog multiplier
• 1x 1N4004 diode

Others

• 1x IDC connector (IDC)
• 3x 1/4" jack connector
• 2x SPDT (Single Pole, Double Throw) ON-ON switch

Ring Modulator main PCB and aluminum front plate pictured in this Instructables were sponsored by JLCPCB, a high-tech manufacturer specializing in the production of high-reliable and cost-effective PCBs.

Their customer service is very good and PCBs a great value for the money!

Without their contribution this module would likely not have been realized so many thanks!