[sdiy-interim] Trivial OTA summing quiz!

[JH.]

>> I'm sure there are are 20 other elegant solutions, but you only gave a
>> choice between 3 or 4. :)
>
>Not with the amount of components given in this particular application! :-)
>With more components then yes.

Fair enough. Or mabe not?

Just as a possibly interesting excercise, try the following:

Omit the opamp completely.

Take a single resistor of 470 Ohm.

Feed the CV at one end of the resistor, and the OTA outputs at the other 
end.
The OTA end of the resistor is your mixer output.

(Draw it on a piece of paper.)

The "circuit" (single resistor) does exactly what you want, except that
(a) you don't have signal inversion for the CV now, and
(b) you have an output impedance of 470 Ohm.

Dependig of your application, (a) may or may not be a problem.
And regarding (b), you often add a 470 Ohm resistor in series to an opamp 
output anyway, to prevent it from oscillating on capacitive loads.
(And well, compared to A ... D, you still have an opamp left for inversion 
and / or buffering.)

JH. 


_____________________________________________________________________
This is the interim list for synth-diy at dropmix.xs4all.nl.
To post, synth-diy at vermine.org
To unsubscribe, http://vermine.org/cgi-bin/mailman/listinfo/synth-diy