[sdiy] buffer opamp configuration [was: 1/8th inch questions]

[Seb Francis]

jhaible wrote:

> I've read RAP's app note now, and apparently he concentrates on _one_ method
> to increase stability: increasing noise gain, with various circuits. But
> this also
> means more noise - sometimes more noise than necessary.
> I normally use the other method, with resistor at the opamp output, and two
> feedback paths, as described in previous mails in this thread.

That's the most common method I've seen for driving capacitive loads - a cap and series resistors in parallel in the feedback loop to get a gain roll off at higher frequencies, with the output taken from the junction of the series resistors.  It would appear that this works for both inverting and non-inverting (gain<1) configurations, but *not* for unity-gain non-inverting - in this case a capacitor parallel with the feedback resistor would have no effect on the gain at higher frequencies .. it's always 1 (I think!).  Hence the alternative technique of increasing the noise gain to increase stability becomes necessary I guess.

It seems unity-gain buffers are tricky, but I can't see any other way with a multi output MIDI2CV - I don't want to add trimmers for each output.

Seb