Effects:

VCA Amplitude Modulation V1

Updated: 091126

This project was created to explore using the SSI2164 Quad VCA as a tremolo. Sound Semiconductor has helpful reference designs as a good starting point. I used the 9V power supply and 4-1 mixer examples in this design: ssi2164datasheet.pdf

After I had those built, I wanted to explore running the same signal in parallel into the mixer, then modulating all of the VCA’s with a separate LFO. This worked better than I expected - musical phase/distortion or clean tremolo if you want it - in either case a musical device that is fun to play with.

I have the CV reference voltage on a separate pot - this is helpful in order to clean the effect up or force it to distort. With this being V1, I will design/build/test the PCB. Once that is complete, I will explore the software side, then update the design with what changes I want to make.

Spread controls the phase relationship for the LFOs. Minimum = locked in phase Max = all phase shifted 90 degrees (I need to double check the terminology here). When I get ready to get back into the software side, I want to be able to have the spread to also be modulated, or not locked in (which is the effect I did first that was awesome), and have 4 different speeds that are offset from 0.03Hz-0.1Hz ish. More on this when I get to the software side.

I could see wanting to add the following (that are not currently included as an option):

  • Multiple Wave Forms to drive the CVs

  • Separate waveform for each LFO

  • More feature rich “Mode” (more on this once I get the first boards in)

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