Several respected synthesists have spoken in hushed tones about how the Moog CP3 mixer is the “secret sauce” (when added in with the Moog oscillator, VCA, and A Certain Filter) that gives Moog modular systems their huge sound. As a result, some have cloned this otherwise simple circuit in a variety of modular formats.

In this video I spend some time with a Eurorack STG Soundlabs .mix CP3 clone, an oscilloscope with frequency spectrum display, and a few different waveforms to figure out exactly what’s going, with tips on how you can apply its particular overdrive characteristics to your own patches to fatten or fizz up their sound (headphones or speakers with good bass are recommended):

 

If you don’t have time to watch the video or aren’t in a place where you can listen to it, here’s the summary:

  • The + output has more harmonic distortion on it than the – output, adding a second harmonic even when not being overdriven.
  • Distortion can start as early as 12:00 on the input dials with a +/–8v oscillator signal. (By the way, the CP3 clips the final signal to +/–6v.)
  • When the + output just starts to clip, the peak of the waveform is pulled up to +6v in the shape of a spike, adding high-end fizz to the sound. This is particularly apparent in harmonically pure waveforms such as sine waves.
  • With the inputs turned up all the way into deep overdrive, the final waveform is heavily clipped. Sawtooth waves get their fundamental harmonic strengthened, adding bass to their sound. Sine waves take on a trapezoidal shape. Square waves…remain square.
  • The CP3 utilizes an old-fashioned “passive” mix bus design, which means there’s crosstalk between the input channels. As a result, turning up one input can appear to reduce the level of the other inputs – the output cannot exceed any one input’s maximum level. At best, this provides auto-leveling of your inputs; at worst, it can yield a sound some have described as phase cancellation.

If you’re trying to reverse-engineer the sequencer patch I used at the end of the video (shown below), here’s some clues:

CP3 video ending sequence patch

For these videos and my upcoming course, I color-code my patch cables in the following way:

  • yellow = audio signals
  • white = 1v/octave pitch control voltages
  • blue = other control voltages and modulations
  • red = gates & triggers
  • green = master sync pulses

As I hinted above, the CP3 does not do much for square waves, but it does wonders for sawtooths. I created a pair of mellow sawtooths (sawteeth?) tuned to octaves using the Doepfer A-113 Subharmonic Generator, and a fizzier sawtooth using the Mutable Instruments Braids VCO set to “CSAW “(it’s supposedly CS-80-like waveform) with Timbre set near 12:00.

The cutoff of the Doepfer A-106-5 SEM filter set to low-pass mode (why the SEM? because I wanted to show you could get That Sound even with an un-Moog-like filter) is driven both by the sequencer and a short AD envelope from the MI Streams.

(No, there is no VCA in this patch; with a brisk sequence of eighth notes that never decayed to silence, there was no need for one – the fast filter envelope with a low initial cutoff was enough.)

I used the internal clock of the Pittsburgh MIDI 3 to sync the RYO VC Sequencer, and also to add as a trigger for the MI Streams. The sequencer goes to the Expert Sleepers Disting in quantizer mode, then to a Manhattan Analog CVP to add a touch of glide. That then goes to the Malekko Performance Buffered Mult to drive the two VCOs and the filter cutoff.

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