[sdiy] Op Amp Buffer stability

[Justin Owen]

-----Original Message-----
From:  [jhaible at debitel.net]
Subject: Re: [sdiy] Op Amp Buffer stability

> Most amplifiers have a range of capacitance where they are unstable / osillating. So you can either stay below that
> critical capacitance, or go above it. For instance, a specific unity gain opamp buffer may be stabe with 10pF on
> its output and with 10uF, too - but not with 500pF.

Thanks Juergen,

You were right - it was oscillation at the output of the buffer op-amp. Locking down some resistor values and replacing temporary pots with fixed resistors seems to have sorted the problem.

For the record - the power supply and the divider were already decoupled and there was never a problem there - which is why I wasn't sure what was going on with this one op amp.

Also - the buffer was feeding VCC/2 to the non-inverting input of 3 or 4 other op amps - but the outputs of all those were just fine.

Sorted now - many thanks.

Justin