CA3140

[Grant Richter]

>
>Why is the 3140 not suitable for the 1k load? It's 
>going to enter an input somewhere with a 100k input 
>impedance right?

The 1K standard output resistor has a number of functions:

1. It provides output current limiting when the tip of the patchcord
touches the module faceplate (ground).
2. It protects the output (to some extent) from things going back INTO
the op-amp output, like static discharges.
3. It allows you to use a simple multiple jack as a mixer for signals,
not a true summer but an averager, good enough for jazz.

The CA3140 won't drive a 1K load under all circumstances, the
output stage is an active current source, and some combinations
of voltages produce base clipping. If you really want to use it
as an output, use a 2K instead. Remember that Bernie Hutchins
is a real methodical guy, his interest is in seeing regularity in his
designs, hence buffer the output to 1K instead of just using a 2K.

Buchla output buffers have the negative feedback tap coming AFTER
the output resistor. This still provides current limiting, but because the
resistor is inside the feedback loop, it eliminates the voltage drop.
Actually more correct as far as getting perfect voltage outputs, but
it doesn't allow you to use trick 3 above.