This discrete 10HP VCA circuit from ACL is unlike any common or classical design, using an entirely different principle.
This VCA circuit enables excellent technical properties such as;
Very low harmonic distortion in the whole linear gain range
No crossover-distortion due to class-A operating mode
No overshooting and ringing due to no use of global feedback for operating point
stabilisation and linearisation, only local feedback used
Low CV-feedtrough due to a very good common-mode rejection
High „offness“, so no audio-feedtrough from the input to the output
High dynamic range, not completely used, to provide some headroom
High bandwidth, completely DC-coupled signal path.
Besides the two individual audio outputs from each VCA, there is also a mix of the output signals of VCA 1 and VCA 2 and of the signal coming from the Aux-input.
The Aux-Input adds an external audio signal to the Sum at unity gain.
For each VCA there is a manual control knob for the gain as well as a Control-CV input.
The Audio and the Control-CV input of VCA 2 is normalled (normalised) to the
corresponding input of VCA 1, so if no cable is inserted in CV or/and audio input of VCA2,
the CV and/or audio signals at the CV and/or audio input of VCA 1 will be copied to VCA 2.
It becomes very easy to create functions like VC Crossfader and VC Stereo-Panorama,
VC FX send, VC Mixer or you can just use both VCA´s individually.