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Tim Stinchcombe's Synth Stuff

 

Stepped CV Generator

This is just a labour-saving module: in order to plot frequency and phase responses of filters, I had been feeding an LFO into an A-160 clock divider, outputs of which went to the inputs of two mixers, with the levels set at binary steps with respect to each other, so that I could slowly step a voltage from 0 to about 8V in 64 steps, this being fed into a VCO, which in turn feeds the filter being looked at. This was incredibly fiddly to set-up each time, so this module does the whole thing: a slow 555-based LFO feeds two 4029 counters (which can be preset to give all outputs high, so I can easily set the full-scale value), and each output feeds a summing op amp whose input resistors are (roughly) 25kΩ, 50kΩ... to 800kΩ. A 4013 flip-flop works as a 'push on'/'push off' switch to set the whole thing running/to stop it running (schematics).

Not surprisingly it gives much more even steps than the manual way, and so produces much smoother filter plots in return. As an example, the following set of plots is from a Doepfer A-124 Wasp filter, as the input CV is varied in half-volt steps:

[Page last updated: 14 Dec 2009]