Re: Interpreting Square Wave Traces



Iain Churches wrote:

"Ian Iveson" <IanIveson.home@xxxxxxxxxxxxxxxx> wrote in message
news:AXLUh.47817$ne6.7862@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
Iain Churches wrote

...
This is a subject that is covered only sketchily in textbooks,
and a common problem faced by many who try to build
a push pull amp with more than a modicum of NFB.

I know of several people who have given up on a
project because they did not know what to do to
tame the beast. My own experience, gained by
purely empirical methods, is that severely
limiting the open-loop bandwidth is a good approach.

Iain,

I still don't think there is such a thing as a square wave...especially
now that storage scopes are cheap.

Please elaborate:-)

Anyway, I would like to pick your brains on another matter almost entirely
unrelated, while you're down in this quiet corner, to avoid a new thread.

When musicians are being recorded, who do they think they are playing to?

Their accountants?

When recording a big band or jazz orchestra, the
saxophones traditionally sit in the front row (they
are regarded as the children of the ensenble) This
is really the worst place they can sit, with the brass
blowing from behind into their mics.

Few musicians like to work with acoustic screens,
so a better studio layout would be to have the trumpets
and trombones at the front and the saxes behind them
in the middle. It is difficult for people to get used to
something different to the standard layout. One saxophone
player said: "I need to see the conductor, to be close to
him" I asked him to persevere. He took his seat centre
and rear, the red light went on, the drummer counted
them in "Two bars for nothing", and the band started
to play, a title that they knew well. Most (including the
tenor player than needed to see the conductor) had
their eyes shut.

PPS One objective of design should be to reduce as far as possible the
need for restriction of open-loop bandwidth.

Yes I have noticed that. Strange that many 60s built amps have quite
a wide open loop bandwidth, and with the exception of a CR across
the anode load of the first stage, and a CR across Rfb, they have no
other step networks, but still exhibit a good margin of stability. Maybe
OPTs were better made in those days?

Iain


Ian says "One objective of design should be to reduce as far as possible
the
need for restriction of open-loop bandwidth."

There is never a need to reduce the open loop BW but the Miller effects
and shunt and series leakage L
will give open loop reductions and phase shift whether you like it or
not.
Hence there is need of reducing open loop gain, and without
drastically reducing the phase shift where oscillations would occur
without such OLG reductions.
Hence the step networks to reeduce gain, but not to increase phase shift
or to reduce bandwidth.

I find Nearly old old amps made in the 60s or before
DO NOT have unconditional stablity, DO NOT have marvellous OPTs, or
anything else special about them
as all were subject to budget constraints and greedy business owners.
Many old bangers oscillated without a load, and had poor margins of
stability
with capacitor loads.

The generally poor standards of gear made in the 50s and 60s is now
being
carefully reproduced in much gear made now.
People are lazy, and they just do not understand anything much anymore.

Patrick Turner.
.

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