Four Quadrant Wave Multiplier / Ring Modulator with Distortion Feedback (Part 1)

This has to be the one of the simplest and most useful modules I've built for my eurorack. The name makes it sound really complicated and I guess it could be if you built it from scratch but I'm using these Analog Devices AD633 chips that do it all for you.

Basic Operation

It simply multiplies two signals together and the '4 quadrants' come from the fact that it has both inverting and non inverting inputs for each channel. Therefore you get (X1 - X2) * (Y1 - Y2).  

This chip also has additional summing input (Z). You can mix another signal into the output of the multiplier or you can feed it back into its self. Always a crowd pleaser. 

So What Does it Really Do?

Like I said before this is really good utility module. It can do a lot of things depending on how you wire it. For example:

• Voltage Controlled Amplifier
• Tremelo
• Ring Modulator
• Wave Doubler (in Theory .. harder in practice)
• Voltage Controlled Mixer (kinda.. this is a stretch)

Here is my basic circuit diagram. If you just want a basic Wave Multiplier then do this. You need a resistor, the AD633 and some switched jacks. The switched jacks ensure that 0 volts is going into the inputs if no signal is plugged in.

I wanted a little more interesting sound so I built this distortion feedback circuit that can be enabled with a DPDT switch. This overdrives the amplifier and provides clipping with the diodes.

Below is how the EuroRack Power header is to be wired.









This whole project can be built in a few hours for less than 50 USD. Here is the parts list:

   6 - S6/BB Mono Switched 3.5mm Jack Panel Mount Solder Tag (Euro Rack Sized)
   1 - AD633
   1 - Circuit Board - 2200 Holes - 160 x 115mm
   1 - Switch DPDT
   4 - Diodes
   1 - 10 Pin EuroRack Power Header

Here it is in operation

I first start using the Maths as a Envelope Generator and use the circuit as a VCA. Later on I increase the speed and it transitions from tremolo to ring modulation. Then you can use another LFO to subtract signals from each other to create beating frequencies. There is also some switching of the feedback switch to add gain and clipping (distortion). Enjoy and let me know what you think.

Next post will show more details on the build of the project.