[sdiy] Combining currents from different OTA outputs

[JH.]

>> A) Could I tie all the OTA outputs together, and run that output
>> down a resistor to ground, and then buffer it with an op amp?
>
>Not a good idea.  Look in the 2164 datasheet for "output
>compliance" ... if you don't know what this means go check H&H (2nd
>ed, page 73).

That's a limitation specific for the 2164, and not specific for summing 
output currents from OTAs.

With any OTA, you must make sure not to exceed the allowed output voltage 
swing, be it to avoid hitting the supply rails (on a 3080), or be it to 
avoid saturation of the output transistor that doesn't have a current mirror 
(on a 2164).
In *any* case, when summing two currents that can add to the double of a 
single output, cut the resistor value in half.

JH.