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

[Justin Owen]

Now everybody's back - I hope nobody minds me giving this a bump...

I'd really appreciate it if you could spare a moment to have quick look over these PDFs to see if you can answer any of the questions below. Most of them are dead basic - but fiddly enough that they need an answer from someone who knows (or at least someone who has an opinion...).

Hopefully your answers will be helpful to more people than just me.

1) Input: http://www.sdiy.org/juz/euro_input_01.pdf

Q: My understanding is the 100R at the socket protects the Zeners from a short when plugging a jack into the socket - is 100R big enough and if not - should I also adjust the impedance setting resistor down accordingly?

Q: Input impedance is set to 100K on the non-inverting config via a 100K to ground. This should be to ground right? Not in series with the input?

Q: On the non-inverting input - is the 100R/100K combo redundant? Can I just use a 100K at the input to look after the zeners and set the input impedance?...

Q:...and if Yes to the above - were would the AC coupling cap go? Between Input and 100K (formerly 100R) or between Zeners and inverting input?



2) Output: http://www.sdiy.org/juz/euro_output_01.pdf

Q: The 100R on the output is to protect the Zeners, again - is 100R big enough?

Q: Again, on the inverting config can the 100R/100K combo be combined into a single 100K at the input?

Q: Again, if yes, where does this put the AC coupling cap?



3) Summing: http://www.sdiy.org/juz/euro_summing_01.pdf

Q: Is there a case for a buffer before the attenuation Pot? If I'm protecting my I/O from unknowns - is it odd to assume that suddenly that input will be prepped to 1K impedance no matter what?



Thanks heaps.

Justin