New filter schematic

[macdonald at evenfall.com]

Hi Michael,

I have wondered the same thing, I have noticed no ill effects from using only
one resistor though.  There may be something about shorting bias inputs to each
other?  Perhaps someone else on the list will have something to say on the
subject.

I have definitely zapped a fair number of OTAs though.  It took me a while to
learn the lesson; unplug the power before modifying the circuit on the
breadboard!  Invariably I will brush a wire or component lead carrying 12 volts
against some some other wire or pin which is connected to the bias input and
*zap*, another 93 cents down the drain.  :-)

-Chris


Michael Lloyd wrote:

> Chris (and others who could answer):
>
> I've seen some circuits using multiple "3080 type" OTAs that share a single
> current limit resistor (R12 in your design), some that use individual
> resistors per OTA and some that use no resistors at all! Is there anything
> magical going on that affects the decision of how to do it? I've read that
> the current control input was VERY unforgiving of mistakes and had a couple
> of bad experiences with shorts, killing the device. So I usually use a
> seperate resistor for each OTA current control input. Plus the extra
> resistors help in the layout from time to time. I'd appreciate anybody elses
> thoughts.
>
> Michael