I am working hard to select the appropriate mux and op amp to use for my CV multiplexer.
As stated in previous posts, the OB6 uses a combination of TL062 and 74HCT4051, very common components. When using these (or actually TL072) on my breadboard I see tiny dips of around 30mV-50mV every time the cap is recharged.
I've tried various op amps for buffering the DAC, different buffer op amps and different mux'es. None perform significantly better than what I have now (on my Saleae scope that is).
Here is a list of what I've tried:
Muxes:
DG4051
CD4051 (worse)
DAC buffer op amps:
TLV9352
AD711
OPA2137
TLC071
CV Buffer op amps:
LT1014
TL062
The only thing I have yet to try is the 8ch DAC used by the OB6. It supposedly does not require a buffer.
This is the config I'm going for:
DAC feeding into a 2x gain TL072 op amp using two 10k resistors that feeds a CD74HCT4051 through a 470R resistor.
The CV buffer is a TL072 with a 1nF C0G cap.
