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Still tinkering with my VCA based effect mixer. I control multiple DACs (MCP4922) which send control voltages to the VCAs (AS2164). Until now I've just fed the DACs a reference voltage of 3.3V to create a CV span of 0-3.3V. Any gain I need is added afterwards by an op amp. Easy but not great regarding attenuation and noise. So to use the full range of the AS2164 VCA i need a CV span from -0.66 to 3.3V

I've read a lot about using an op amp to scale and offset, but still a bit puzzled. I could really need an actual example that is close to what I need.

I have +-9V bipolar source to drive my opamps and VCAs And I have a +5V source to drive my digital board.

My thought is to feed the DAC a 5V reference which will give me 0-5V DAC output. So how do i get from 0-5V to -0.66 - 3.3V?

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    \$\begingroup\$ Why didn't you choose a DAC that can be an actual VCA in its own right? They are called multiplying DACs and although not as common as regular DACs they would make life simpler I expect. \$\endgroup\$
    – Andy aka
    Commented Feb 26 at 9:20

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You have an input range of 5 V, and an output range of 3.96 V so you would need to have a gain of 0.792. That will get you 0 to 3.96 V, then you need an offset of -0.66 V, that will get you -0.66V to 3.3 V. The offset will need to be scaled by the gain as well. It can get a bit tricky when you're subtracting because the inverting and non-inverting inputs will have different gains. Luckily there's a document from TI that tells you how to go about the whole process, follow the instructions and you should end up with what you want. You'll need to have a stable reference voltage to derive the offset voltage from.

Designing Gain and Offset in 30 Seconds

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