S&H

[John Speth]

Some 15 years ago I built a circuit that stored 64 voltages in 64 caps using 8 4051s for muxes and TL084s and polystyrene caps configured as S/H's.  It was driven digitally by 6 bit address and 8 bit data with a strobe signal.  When you write the data you select an output address and data value and it wrote it to a SRAM chip.  It had a counter that freely cycled through the SRAM, read each value stored and output it to a DAC, selects the addressed mux line which "loads" the cap voltage from the DAC.

The idea was that the counter simply refreshed the caps as fast as it could.  The hardest part of the circuit was the SRAM read/write arbitration.  Using modern components I'm sure I could make it simpler and more accurate.  A PIC could do almost all the logic work.

It worked real well.  The counter would refresh each cap every 10 usec so you could use really small caps and opamp input impedance was not a big deal because leakage was minimized due to the fast refresh rate.

Using something like the Peavey PC1600 and putting a MIDI front end on a design like this would be a nice "pot reduction" thing as far as CVs go.

John Speth
Object Engineering, Inc
mailto:johns at oei.com