I’m building the alfa4 VCAs using the AS3360 dual VCA chip. I initially planned to use two chips to give me 4 VCAs, but realised I could use the velocity out of the MIDI-CV module to make things more interesting, so decided on 4 chips to give me 4 dual VCAs.
I redesigned my panel accordingly and set to work designing the circuit.
It’s “heavily” inspired by the Kassutronics Dual VCA, though I have made some changes. There’s only one audio input and the switch on the output jack of the first VCA feeds into the second. I also added a fixed voltage to the switch on the velocity input jack, so the velocity attenuator opens up the second VCA if there’s nothing plugged in there. There are separate outputs for pre- and post- velocity, with only the post-velocity signal being sent to the mixer if no jack is plugged into that output. I also added an LED to indicate the output signal.
I made up a stripboard layout for the circuit – I’m actually quite happy with this one, which is a first!
I also put together a schematic for the mixer section – this was my first go with KiCad, so apologies if these are suboptimal!
I made up a layout for the mixer as well, which I’ll add to a board along with the power, which will use the same power bus as my other quadules.
I went ahead and built all of the circuits. I was pretty confident with the design, so I didn’t feel the need to test one out before just going for it!
I printed out my panel design and used it as a guide to drill the panel by hand, then labelled it up.
I also tested out the sandwich construction to make sure everything fit together properly and fit in the case, which it does.
I tested all the circuits and they’re all working fine – there was an issue on my first test with a cold joint on one of the CV inputs, but I found and fixed that and everything works perfectly now.
Just waiting for some more B100K pots to arrive from China, then I can finish this off…