ACL - Variable Sync VCO


ACL’s Variable Sync VCO is an analog oscillator with ramp-core design. The module produces five waveforms, which are emitted via individual outputs. A three-way switch allows users to roughly set the frequency range. For precise fine adjustments, there is a ten-turn potentiometer. In addition to the obligatory 1V / octave jack, the Variable Sync VCO features one linear and two exponential FM inputs with attenuators. The pulse width can be modulated as well. A voltage-controlled threshold parameter in the module’s sync channel makes it possible to blend from deactivated to soft and finally hard synchronization.
In use, the Variable Sync VCO shines with voluminous sound reminiscent of classic keyboard synthesizers. The sine waveform is exceptionally clean. Slight pulse width modulations lead to extremely fat results. Linear FM modulations sound very full and wet. The sync function can generate a wide range of harmonics structures thanks to the variable threshold.



The Variable Sync VCO generates five waveforms, which can be tapped at individual outputs. In detail, the following waves are available:

  • Saw tooth
  • Inverted saw tooth
  • Triangle
  • Sine
  • Pulse waves with variable width

The oscillator’s frequency range can be set via a three-way switch. With the lowest setting active, the circuit operates as a LFO. Via a potentiometer with ten turns, users can fine tune the VCO. Besides a 1V / octave socket, the module features one linear and two exponential FM inputs with dedicated attenuators. The pulse width can be controlled manually and via control voltages.

An important highlight of the Variable Sync VCO is its flexible sync channel. The threshold parameter allows users to comfortably blend from inactive to soft and hard synchronization. Thanks to a CV input pus attenuator / polarizer combination, this process can also be controlled via, for instance, an LFO, envelope or modulation sequencer. With the threshold potentiometer turned completely clockwise, the oscillator core will lock. It can be freed via a control voltage at the corresponding CV input. The results are interesting “pulse-train sounds”.


1v / octave input
Linear FM input
Two exponential FM inputs
Sync and PWM inputs
Sync CV input
Five waveform outputs


3U Eurorack module, 16 HP wide, 22 mm in depth
Power consumption: 40 mA at +12 V and 35 mA at -12 V

0.197 kg
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