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CV level shifter & attenuator


NorthernLightX
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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.

 

 

 

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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.

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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.

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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:

level_shifter.png

 

level_shifter_board.png

 

 

(Pad1 and Pad2 are there to accomodate different pin space potentiometers)

Edited by NorthernLightX
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