In article , mick
wrote:
On Mon, 10 Aug 2009 16:49:38 +0100, David Looser wrote:


Arggh!... Plonking a 1nF capacitor across the output of a feedback
amplifier is a pretty likely way of making it unstable


:-)
I always knew there was a reason for zero-feedback amps... ;-)

Alas, they may not actually exist except as a wish. :-)

Even individual gain devices can burst into oscillations. Indeed, I've
spent years getting circuits with just one diode to do that. :-)



Ideally there wouldn't. But what makes you think that there isn't?.
With active devices having good gain up into the hundreds of megahertz
what makes you think there isn't noise, RF pickup and self-oscillation
well above the audio band present?



A good point. It does make it rather difficult to design unconditionally
stable audio amps if your test gear can't reach those exotic heights!

Eee... when I were a lad 30MHz were *proper* RF!

Me too. But I've since spent decades working on the basis that anything
much below 30GHz is 'IF'. 8-) I recall once using a system with an IF
bandwidth of over 10GHz and thinking how many of the usual comms bands,
etc, could be fitted into that IF - if upconverted into it. :-)

BTW M$ free here also. :-)

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html