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
Option 1 : non-inverting adder.
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