# Unipolar to Bipolar CV

I want to offset a unipolar CV output to a bipolar CV. Specifically, I want to take the Pitch CV Out of a Minibrute, which is 0 to 10V and offset it to -5 to +5. This is something I would like to make into a circuit. Would this just basically be making an attenuverter? I surprisingly don’t have much experience with them.

You may want to look at MidiALF CV output section here – it translates 0-5V DAC_CVn output to 0 +10V or -5 +5V short circuit protected CV output depending on the CVn_OFF level signal (0 or +5V).

Your case does not require x 2 voltage scaling, so you’ll need to recalculate input and feedback resistors however since selecting identical resistors is much easier, just use a voltage divider to get Midibrute’s CV down to 0 + 5V

No attenuation should be involved: you want the signal to keep the 1V/Oct scale. If the signal jumps by 1V on the minibrute side, it should jump by 1V exactly on the output. So the gain should be exactly 1.0000

All resistors equal, 100k, 0.1% appreciated.

V1 is the output from the Brute ; V2 is -5V. You can generate -5V with a divider form 12V (silly) or with a 5V LM4040 mounted backwards (C6 on the last page of the Anushri schematics adjust the 470ohm resistor depending on your current consumption).

Option 2 : two stages of inverting.

If you have more signals to add (transposition CV input?), it might be easier to just use the common inverting summer ; and then another stage to invert it back.

Think of it as a standard summing circuit, you just sum you CV and -5V.
R1 and R2 “isolate” the Inputs from each other, R2 and R4 are a Voltage Divider that determine the Gain, 100k is a perfect and common value, but this will work with pretty much any decent value you have at hand if its great enough.

Getting the -5V is the hardest part, as pichenettes points out you should not rely on the -12V Rail and a Pot, thats bad habit and only acceptable for CVs, by no means for Pitch CVs. Any fluctuation on the rails would influence your CV.

Thanks for the details! Think I have a couple of those 4040s laying around. I’ll breadboard it hopefully later today. I knew you guys would stear me right. Highfives

Add some decoupling caps at the rails….

Well that goes without saying of course