PCB/PANEL - OTAVCA dual linear VCA (4HP)
4 in stock.
THIS IS A PCB/PANEL SET - you will need to source appropriate components to complete the build. It is assumed you know how to read a BOM and a schematic and troubleshoot any potential issues
The BOM, schematic and calibration notes can be found here: https://github.com/yorkmodular/otavca
The LM13700 is one of those chips that has been knocking around for years, minding its own business, despite the fact that it is a mind-bogglingly useful and versatile piece of silicon. Granted, it can be a bit of a pain to work with, but it's still useful nonetheless.
This is a dual VCA, each channel of which uses one of the transconductance amplifiers on the 13700. Other than the addition of a couple of linear current sources for CV control this isn't massively different from the circuit you'll find in the datasheet. It works best with signals in the +/-5V range, although it's relatively unbothered by particularly hot CVs from envelope generators.
Is it perfect? No - far from it; depending on your envelope generator there may be a bit of CV bleedthrough, but then if you want ultra-high fidelity then you're probably better off with the THAT2180, which has a unit cost about 10x that of the LM13700 ... that being said, they work well enough that I actually keep a couple in my own system.
Personally, I find that the LM13700 gives a bit of warmth to a sound, but that could just be me ...
On a technical note, the CV LEDs are driven through the on-board buffers on the LM13700, so require a fairly high voltage to illuminate, so if the CV level is particularly low you may not see any illumination - I've yet to decide whether or not future runs of the board will incorporate the LEDs; the current run will. In addition, both channels are set up so that unity gain occurs at 5V - you can modify this via the GAIN trimmers if you like, but having a couple of attenuators handy may be a good idea depending on what your CV levels are.