in preparation of the MB6582 with redesigned AOUT, that will be configured for +/- 5V CV signals, I am looking at some circuits to put in front of existing modules that are expecting CV signals of 0v to +10v. For extra flexibility/compatibility I’d like to have the level shifting switchable, and the input CV signal attenuatable (nice scrabble word by the way )
- the +/-5V input CV signal is fed to the upper input, this has an attenuator as well
a +5V signal can be switched on for the second input
The only thing this doesn’t yet have is protection against over voltage and negative voltage. For over voltage protection a 10V zener diode is probably the answer, but what about negative voltage? I don’t want to damage the circuit behind the level shifter.
Yes that’s helpful indeed! I need to invert the summed voltages anyway, so doing that with a rail-to-rail opamp could be an easy solution to do the inverting and the protecting in a single package.
For the supply rails I don’t have a +10V supply available but a voltage devider could be calculated for that.
After re-reading some of the info on the 2164 board it seems the module is fine with a CV voltage of 11,67. I think it will handle the 0,33V over voltage as well if the “protection” opamp is powered by 12V, so no need to create a separate 10V supply. Less parts is good .
I’m searching for a good single supply rail-to-rail opamp for the voltage follower. LM324 is a cheap choice but performance is not so good, I’ve read it can’t go all the way down to ground, so +0,3V is the lowest you can go with it. MC3403 is an alternative, but I can’t find if the performance at ground is much better. Suggestions are welcome.
Anyway, I’ve been drawing and thinking and some more drawing and I think I have a solution that does not require a rail to rail opamp. One schottky diode as a negative voltage protection is sufficient. Proposed schematic and board:
(Pad1 and Pad2 are there to accomodate different pin space potentiometers)
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