In addition to the good suggestions others have made here's something I've
seen often.

If the load you're driving has too much capacitance you can get oscillation
on the output of most op-amps. With a LM324 type it takes only a few tens of
pF to make the output oscillate. Some op-amps can tolerate a lot more load
capacitance. To decouple the op-amp from the capacitive load simply add a
small (10 to 100 ohm) resistor in series with the output. If the series
resistance causes too much drop in the output you can move the feedback
takeoff from the output pin to the other side of the resistor. National Semi
used to have a good description of this problem and cure in the LM324
datasheet.


Paul

> I have built a volume control circuit using opamps and a digital pot.
> The opamps I am using are NE5532N. The input buffer and output driver amps
> are configured as inverting amplifiers. This is so I can add gain later if
> need. My problem is that as the circuit reaches unity i.e.
> digital pot is at
> 0. The input amp has a hi frequency osc. This is not audible nor does it
> noticabley affect the audio but should not be there. I have read somewhere
> that I should have some capacitance somewhere to stop this but
> can not find
> the reference :-((

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu