Dual Decay Envelope & VCA


The front of every ski has a form of a curve similar to a decay envelope. The Skis module has two channels, A and B, and each of them consists of a decay envelope with knob control and a VCA. There is a TRIGGER input to trigger the envelope, a buffered envelope output, which is normalized to the CV input of the VCA. Then there is SIGNAL IN and OUT of the VCA.

Use Skis to Generate Drum Sounds with Adjustable Decay

A typical application of Skis is to take two signals (noises, for example) and generate drum sounds with adjustable DECAY from them with a TRIGGER signal. However, you can also use the two VCAs and two DECAY envelopes independently.

There is also a CRUNCH switch, which activates a special mosfet lo-fi VCA circuit inspired by the designs of Standa Filip. This adds a slight crunchy character, which changes with the decay of the envelope.


  • dual decay envelope with adjustable decay time (trigger input, CV output)
  • dual VCA (signal IN, signal OUT, CV IN is normalized to CV output of decay envelope)
  • crunch feature inspired by circuits of Standa Filip
  • jumpers for changing the decay envelope to release envelope (VCA is on full while there is a gate signal and than it decays)
  • jumpers for enabling the decay knob to completely mute the decay envelope
  • jumpers for selecting weird filtering of the output signal (also inspired by Standa Filip)
  • front panel from aluminium or oak wood with custom knobs
  • handmade locally by Bastl Instruments in Brno, Czech Republic

Technical details

  • 5 HP
  • current: +12: <30mA, -12: <20mA
  • 35mm deep (skiff friendly)
  • PTC fuse and diode protected 10 pin power connector
  • pdf user manual download

DIY kit

You can build your own Skis with our DIY kit. Go through the complete assembly guide below and make sure that you understand all the steps.