[sdiy] ...that 1K resistor on the output

[Neil Johnson]

Hi Justin,

> Last week I was asking about passive vs. buffered multiples.
>
> A few of you mentioned that you put a 1K resistor on the output of all op amps (or all outputs...) - can I ask: Is that in series i.e. between the output of the op-amp and the actual output or from the output of the op-amp to ground i.e. load?

Series.  The idea is to raise the impedance of the output so you can
not-quite-mix signals together, although its not a true mix - if you
wanted that then you'd need to use high-impedance current outputs and
low-impedance current inputs - in other words create a mix-bus.

Its only really a good idea on audio outputs.  If you have CV outputs
then the 1k resistor introduces a 1% error when driving a single 100k
input, 2% error when driving two 100k inputs in parallel (via a
passive mult), etc.

> And secondly - for AC-coupled outputs are you running op-amp > resistor > capacitor > output or op-amp > capacitor > resistor > output?

Doesn't matter, they're in series.

Cheers,
Neil
-- 
http://www.njohnson.co.uk