I've just finished the first proto of my new module - a quad VCA based on the SSM2164 IC 8). The 2164 incorporates four high quality VCA channels with logarithmic response and is one of the few highly integrated synth-related ICs which is still in full production (by Analog Devices).
The logarithmic response is kind of unusual for a synth VCA and not very suitable for modular synths (because most envelope generators already output exponential CVs - some reading: http://www.synthmuse...ne/linexpo.html). But for use as a (final) VCA e.g. of a Midibox SID, the log response is perfect - the CV generated by routing an envelope without tweaking the curve parameters to an AOUT channel is linear so the ssm2164 will give the same change in dB for the same relative value change over the full range.
While not as obviously exciting as a VCF, a VCA is a very useful addition - e.g. it serves as a noise gate for 6581 lovers like me, adds the possibility for true velocity sensitivity. Another great effect in conjunction with a VCF like my SSM2044 module: if you set the VCF to full oscillation with max keytracking, you can use it as a fourth (sine wave) oscillator. Sound demos to follow in the next days
The module is 50x80 mm in size, parts cost is about 10-15 Euros (for four channels! )