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

[Harry Bissell]

more...
----- Original Message -----
2) Output: http://www.sdiy.org/juz/euro_output_01.pdf


hmmm this could take years to go through. Better to make a file of each individual schematic instead of many on one page so its really clear which
one we are referring to.

In general, your first two schematics with the 1K resistors at the output don't make a lot of sense. That feedback configuration is used to compensate
for the voltage drop in the series output resistor, and you have two of them, spoiling that effect. I would throw those out of consideration.

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

same answer as last post...

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

here its 1K and 100 ohm right ? One resistor is protecting the zeners from an externally applied voltage at the output, the other is protecting against
the opamp trying to drive above 10V output. I'd make them both 500 ohms if this is what you intended. There are better ways to limit an output to 10V if that is what you want. Zeners in the feedback of the opamp is one way. That could use just one resistor in series with the opamp output to protect
the opamp output. If you tried to drive a voltage into the output, the opamp would drive to keep the voltage within the 10V range set by the zeners.

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

I'd put the cap after the series resistor at the opamp output (so the opamp does not see the capacitive load directly) and add a 1M resistor
to ground at the jack end, to prevent thumps as you plug in.

You might want to search some of the stompbox forums to see how they handle capacitors, They are almost always on a single supply and have to
deal with both ends of the cap as a rule... (or they blow a lot of speakers :^)

More next post...

H^) harry



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

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-- 
Harry Bissell & Nora Abdullah 4eva