CV level shifter & attenuator

[NorthernLightX]

Hi all,

 

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 :rofl: )

 

I have found this schematic on the MFOS website: http://www.musicfromouterspace.com/analogsynth_new/HOT_TIPS/PDF/DCCoupledLevelShifter_assembly.pdf

 

I've come up with the following scenario:

- 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.

 

 

 

[Shuriken]

Maybe this topic helps

[NorthernLightX]

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.

[NorthernLightX]

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 :thumbsup:. 

[NorthernLightX]

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.

[Shuriken]

What is wrong with the TLV274?

[NorthernLightX]

What is wrong with the TLV274?

 

Reichelt doesn't carry it :whistle:

 

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)

Edited January 7, 2013 by NorthernLightX