Brian Tuley

The core of this module is based on the NE570 Compandor IC. There are 16 pins on the dip. Each side of the ic will serve as a single VCO. I will use a second ic to get a total of 4 independent VCAs.

Schematic which I used to build from.

Initial breadboard of a single VCA. I have debugged it and everything meets expectation. Performance meets expectation. I have added a resistor across the signal input so that the module is completely silent at CV=0 volts. Next, I will scale this design up from a single vca, to a quad vca full module.

Here I have implemented the quad VCA's. I'm using both sides of the the chip. There is a VCA on each side of each IC.

The leads are short, but everything fits just barely. Of course I could have ordered a Thomas Henry PCB for $20.00, but I get a little more satisfaction when I build a module from the ground on up. It takes a lot more time, but it's a fun challenge.

Plenty of cable ties are always useful. I'm getting a little better at laying out my components on the board.

Alternate view.

Side view. Note the 2" standoffs. These are a good length to clear any jacks or pots which are beneath the board.

Testing the unit against the full modular system. Note the HexInverter Postman EG that I'm testing against. It's a good unit to test against, as the output gain is a higher than my other EG's. I will calibrate my design to optimize performance to complement the Postman EG. I plan to often make use them in conjunction with one another.

The module works great and it will serve me well in years to come! It is especially useful with the Hexinverter Postman Envelope Generator that I use. The postman is a basic utility envelope x 4, and this vca is a basic utility VCA x 4. The Postman envelope generator features simply attack and decay envelopes, and this VCA is not exactly precise. In testing, this VCA responds very well to Attack and Release CV control, but it falls short in the Decay and certainly the Sustain area of performance. But that's OK. I have a Synthesizers.com VCA for precision and the Mattson Quad VCA which offers four more VCAs for the delicate synthesis. For drums or standard synthesis, this module is more than enough.

I have re-purposed the front panel that I was using for the Mattson VCM that I built in 2014. All that was needed was to remove the Mattson PCB and make sure my DIY perfboard would fit on the standoffs upon completion. I used some lighter fluid and a cotton swab to wipe away the cascaded switching jack stencil that no longer holds true. I also needed to add two additional output jacks, as the VCM only had two outputs. 1 for non-inverting and a 2nd output for inverting.