ACL – Variable Sync VCO

Audiophile Circuits League Variable Sync VCO
Width 16 HP
The ACL Variable Sync VCO is a precise, excellent sounding VCO, providing five simultaneous waveforms, a VC variable-sync feature, deep linear FM and more, and all with precise tracking and low temperature drift. There are any number of treasured components in our modular system, and it’s a thankless task to rank them, but anything that generates audio deserves a place at the head table. Out of respect for this honoured status, we’ve tried to do some particularly cool things with our Variable Sync VCO, and push it to some uncommon extremes.
First thing’s first though: These oscillators sound great, with exactly the kind of classic raw vintage synthesiser tone you’d wish for. The sound is derived from one ramp core oscillator, with several waveshaper subcircuits, allowing saw, inverted saw, triangle, sine, and rectangle. And since we only like randomness and unexpected results on our terms, exclusively at times of our choosing, consistent tuning is the name of the game.
There’s more to life than tone and tuning accuracy, so additionally, when synced to another VCO, the degree of synchronisation (i.e. soft-sync, hard-sync) can be set manually by knob, or by an external CV. In other words, this lets you morph between soft- to hard-sync. Which is pretty nice. There are many fun results to be had here. For example, you can modulate the Sync Threshold to create a variety of effects, such as ‘pulse trains’ or crazily stuttered waves, for a weird, bizarre, and wonderful world of sci-fi sound. Used in conjunction with frequency modulation, this can introduce fascinating harmonics to otherwise harmonic-free sine waves.
Plus, we don’t want to show off, but the linear FM modulation amount is quite huge for this type of VCO. And the input for linear frequency modulation is AC coupled (enabling very high modulation amounts with minimal drift off the center pitch) and configured like differentiator.
If all this is going over your head, it essentially means minimal detuning is introduced. The VCO features low, middle, and high modes, which, together with the 10 turn precision Tune pot, results in a very convenient on-the-fly ay of tuning the module. The frequency can be modulated exponentially from two CV inputs.
There is so much more to say about the Variable Sync VCO, and we invite you to check out the PDF manual for more details, but VCOs should be judged as much on their sound as their features, so we also urge you to listen to some of the audio demos to hear it in action.