The Oakley RM-4014 Ring Modulator
This is a vintage ring modulator design with bags of character. It is based on the classic
ARP4014 sub-module which was used on the ARP2500 modular and ARP2600 semi-modular
synthesisers. The design has a fully discrete core but uses two op-amps for input and output
amplification.
A ring modulator has two main inputs, usually called X and Y, and one output. The output
voltage is the product of the two input voltages. In other words it multiplies the two input
signals together to produce a new and different sounding output. If you have two sine wave
input signals then the output will have both the sum and difference frequencies. For example,
if X is a 440Hz sine wave and Y a 40Hz, you would get a 480Hz and a 400Hz sine wave from
the output. However, this is only really true in a perfect ring modulator, and this ring
modulator is not that. Each input has its own differing non-linearities or imperfections. This
greatly adds to the character of the resultant output.
The Oakley Ring Modulator features three rotary control pots. Each input has its own
attenuator, and there's also a offset control for the Y input. In conjunction with the Y
attenuator, this third pot effectively acts as a wet-dry control for the X input. But because of
the non-linearities inherent in the design it also acts in more subtle ways.
You can also use the Oakley Ring Mod as a standard VCA. Just use the Y input as your CV
input and X will be shaped accordingly. Each input can be either direct coupled (DC) or high
pass filtered (AC). The former allows DC and low frequency signals to be processed. While
the latter provides a DC block to process only alternating frequencies. The standard panel
design makes both types of input available with each having its own socket. You can use both
inputs on each of the X and Y inputs at the same time. Input signals will be summed together
so you can also use the RM-4014 as a simple audio mixer.
This is the prototype issue 1 RM-4014 Ring Modulator module behind a natural finish 1U wide MOTM
format Schaeffer panel.
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