Don Pearce wrote:

Eeyore wrote:
Jim Lesurf wrote:
Rob wrote:
Jim Lesurf wrote:

FWIW it means very little to me. You seem to assume a correlation
between frequency, resistance and sound.

Not sure what you mean, I'm afraid.

That much is apparent. Doubt you know much about the concept at all, nor the
bases of stability.

Can you explain then? It has me puzzled too. And given Jim's
background I am going to tell you he knows precisely what stability
means, and how to measure and predict it.

How many amps has Jim designed that have sold in the many tens of thousands ? And
been VERY reliable.


Stability circles are the second thing you learn about on the Smith
Chart.

And there's far more than one way to make an amp stable other than simple
dominant pole compensation. Just the output stage configuration and topology ( to
take yet another aspect ) can make a VAST difference. I actually got 'caught out'
once designing a new amp where the DC beta of the output devices was more than
adequate yet the load impedance would reflect back to the last voltage driver
stage, affecting phase margin.

Result, one extra emitter follower stage added and NO load would result in phase
related instability. The voltage driver stage's load was essentially constant as
a result of the change. It's not difficult really once you get the hang of it.

Graham


--
due to the hugely increased level of spam please make the obvious adjustment to
my email address