[sdiy] The annual I/O impedance/protection thread! (revised)

[Justin Owen]

Based on the advice Harry B gave yesterday (thanks again Harry...), I've revised and uploaded new schems for my Eurorack Input, Output and CV Summing.

http://www.sdiy.org/juz/euro_input_02.pdf
http://www.sdiy.org/juz/euro_output_02.pdf
http://www.sdiy.org/juz/euro_summing_02.pdf

Go take a look - go pull 'em apart.

I made the following changes:
1) Added 1M to ground at socket on all I/O to stop pops and thumps
2) Moved the AC Coupling cap to become the first component in series with the socket - placed after the 1M de-thump resistor
3) Set value of Zener protection resistor according to the relationship between expected input overvoltage/current, power rating of the Zeners the resistor is meant to protect and the required input impedance
4) Added optional 1M Resistor to Ground to taylor the curve of the two CV Pots on the Summing config

I hope I got that all right...

I still have a couple of questions:

1) Non Inverting Input
Does the 1M at the input affect the Impedance?

2) Inverting Input
If the Impedance of this input is the sum of the 100R Zener protection resistor and the 100K resistor at the inverting input of the op amp? At some point, if I raise the 100R high enough to provide better protection for the Zeners - I would have to drop the 100K to compensate and to keep the impedance close to 100K?

I'd still be up for any input on this...

Thanks - much appreciated,

Justin