[sdiy] Op Amp Buffer stability

[JH.]

If there isn't any noise that bothers you, you don't the cap on the resistor divider. But if your application is sensitive to noise, 
that cap is the first thing I'd put in.
10uF on the power supply rails are just like the 10uF at the output of an opamp buffer: They won't filter the reference / voltage 
regulator noise, but they help decoupling the loads (to some degree), and they are required to keep the regulators stable.

JH.

----- Original Message ----- 
From: "David G. Dixon" <dixon at interchange.ubc.ca>
To: "'JH.'" <jhaible at debitel.net>; "'Scott Nordlund'" <gsn10 at hotmail.com>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, September 25, 2009 1:02 AM
Subject: RE: [sdiy] Op Amp Buffer stability


> It's not an either - or.
> Putting a cap on the divider filters the reference, and goes without
> saying / should always be done.

Oops!  I guess it 'doesn't' go without saying, because I've never done it.

However, if I have a pair of 10uF electrolytics on the rails just downstream
of the power connector, do I then also have to filter the rails again at any
reference dividers?  I would have thought that one pair of big decoupling
caps on a board was enough.