£159.00 (£132.50 ex VAT)

Discrete JFET-based VCA (Voltage Controlled Amplifier) which can be tastefully (or violently) overdriven for saturation/distortion effects. Also includes a Zero-Crossing detector, and CV output to pass the modified CV signal to other devices


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SKU: persephone Categories: , , ,


The Expert Sleepers PERSEPHONE is a VCA (Voltage Controlled Amplifier) using a discrete JFET as the gain element. The JFET can be tastefully (or violently) overdriven for saturation/distortion effects.

Persephone also includes a Zero-Crossing detector, which can be used to restrict gain changes to zeros in the audio waveform, preventing clicks and pops that can occur with very fast envelopes, especially on lower pitched sounds. In fact, with the zero-crossing circuit engaged, you can use a simple gate as the CV input without clicks.

Audio path

  • The two audio inputs are summed (mixed), and then pass through three gain stages: the Pre stage (i.e. pre-VCA), the VCA itself, and the Post stage.
  • The purpose of the Pre stage is primarily to reduce the input level to one that the VCA can handle with reasonable linearity; likewise the main purpose of the Post stage is to boost the signal back to normal levels. Conversely, by deliberately raising the gain of the Pre stage we can deliberately operate the VCA in its non- linear (saturating) region; then the purpose of the Post stage becomes that of reducing the level so it doesn’t clip at the output.
  • The Asymmetry switch disables part of the circuit that linearises the behaviour of the VCA, resulting in positive and negative sections of the input waveform being processed quite diferently, increasing the even harmonic distortion.
  • The whole audio path is DC coupled.

CV path

  • The two CV inputs are summed, one via the attenuator, and passed to a Sample-And-Hold circuit. If the zero-cross detection is not enabled, this simply passes the CV straight through.
  • If the zero-cross detection is enabled, the CV is sampled whenever the audio signal passes through zero, and that CV value is held in between zero-crosses.
  • The CV output is the output of the S+H circuit.
  • The Bias is added to the CV from the S+H and the result is used as the controlling voltage of the VCA.


    • CV input (with attenuator)
    • CV input
    • Two audio inputs (summed)


    • CV output
    • Audio Output


Width: 8hp
Depth: 37mm
Power: 33mA @ +12v / 26mA @ -12v