[sdiy] CV input circuit

[Roman]

The pots set mean values from where CV are bending up and dowm. Yes this is summing circuit.  And yes, you cound do that bias summing before opamp, not after, then inputs would have some useful impedance, depending on what resitors are used. In this circuit the input impedance is very high, you can easily have over 20Vpp power hum wave at the output of the opamps just by touching the tip of a patchcord slightly.   Why this is done that way I don't know. Is it for guitar pickup maybe?  And if you want to study opamps, you should read Analog Devices application notes, rather than look into eurorack modules schematics.   Roman  Dnia 14 maja 2018 18:27 Corey K <  coreyker at gmail.com > napisał(a):  I've been studying a few open source circuit designs for digital eurorack modules, and I've come across one that I'm having a little difficulty analyzing. It is for the 4ms spectral multiband resonator (SMR). In particular, I'm looking at circuits for the MORPHCV and SPREADCV inputs, which are on sheet 4 of the schematic (left hand side):    github.com github.com   I understand the basic parts of the circuit: the input passes through and op-amp buffer (gain=1), and the output is connected to a 5v source via a trim pot. The input to a microcontroller is clipped to an acceptable range [0, 3.3V] with two diodes.    I guess I'm having a bit of difficulty figuring out exactly what the voltage will be at the MORPHADC and SPREADADC pins. I tried to do some nodal analysis, but things weren't making sense to me.   My intuition is that this is some type of "summing circuit" (the current from the 5v source gets added to the current from the op-amp). If so, why wouldn't the designer have used a traditional op-amp summing circuit? What might be preferable about this configuration?   Thanks,  Corey    ______________________________  Synth-diy mailing list   Synth-diy at synth-diy.org  synth-diy.org synth-diy.org
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