In article ,
Patrick Turner wrote:
On Jun 26, 2:25*am, John Byrns wrote:
Now the obvious question is, why bother with this extra complexity when we
could
simply directly move one of the 3 poles to a very low frequency, as would
probably be part of the normal pole staggering process anyway? *I will
leave
that for others to comment on as I have not personally mucked about in my
workshop with amplifiers that have 3 LF poles. *I suspect that one reason
may
have to do with LF overload when using a Bean Counter approved OPT.
Its not always convenient to move poles down, and often it merely
moves the oscillaton F lower. It can be exasperating to find that even
if you increase coupling caps from say 0.22uF to 2.2uF, the trace on
the CRO still slowly rises and falls because Fo has just gone lower.
Hi Patrick,
The phrasing of your comment suggests that you are speaking of moving all the
poles down, in which case as you say "Fo has just gone lower". What I was
considering was moving just one pole down in frequency. This leads directly to
the question of how you choose your pole frequencies? You have explained how
your LF shelving network improves LF stability, although with the risk of
pushing the input stage closer to overload, what you haven't explained, at least
that I remember, is how you choose your pole frequencies, especially in an
amplifier with 3 poles like we are discussing?
--
Regards,
John Byrns
Surf my web pages at,
http://fmamradios.com/