keithr wrote:
>
> "Trevor Wilson" <trevor@[EMAIL PROTECTED]
> wrote in message
> news:67k7ilF2onhd7U1@[EMAIL PROTECTED]
> >
> >> Good transistor amps function perfectly well with wider tolerances
than
> >> you say because of the abundance of
> >> local and other NFB.
> >
> > **"Good" is your term. not mine. I happen to feel that amplifiers
which
> > use lots of Golbal NFB are not "good". They are average.
> >
> > Trevor Wilson
>
> Speaking as one who has never seen, heard, or even smelled an ME amp
perhaps
> you can clear something up for me. As I understand it the ME is made up
of
> several modules in the signal path. Each of these modules has it's own
> feedback loop. Assuming that the module and it's feedback path are
correctly
> designed and thus pass an undistorted signal to the next downstream
module,
> why does this require such tight tolerancing in the output stage? I do
> assume that the ouput stage module has it's own feedback loop and is
being
> fed an undistorted signal. After all, even with global feedback, I know
of
> no design that takes the feedback loop back to the input of the pre-amp
so
> it is not entirely global even in that case.
>
> Keith
You have invited an utter bull**** artist, ie, Trevor Wilson, to spew
all over you.
Good luck.
Water restrictions prevent me using a hose to clean you up after Trevor
does his bull****ing and spewing.
Note that whatever he says isn't referenced in any way to a schematic of
an ME amp
which you are able to inspect.
It is all sales talk and self agrandisement.
Trevor has never designed or built an amp in the last 30 years.
I seriously doubt Trevor Wilson has ever read a book about amplifier
design in his life.
Your questions require a very well detailed long answer with a schematic
reference,
and this is what you will NEVER GET from a dumb **** like Wilson.
But lemme say that it is supposed by somebody somewhere that well
matched output
transistors assist in getting low crossover distortion switching
artifacts
and low macro artifacts from disimilar hfe and gm on each side of the PP
circuit
where a complementary Ziclai pair of NPN and PNP transistors are used.
The Sziclai output arrangement in ME amp output stage is difficult to
describe in words,
but there is a ****rt and trouser load of NFB involved. A schematic is
need to get the picture.
Where output transistors have been paralleled on each side of the PP
circuit
in groups of NPN and groups of PNP types, matching reduces open loop
distortions
if differences between all NPN and between all paralleled PNP are
minimised.
But for full benefits, differences in hfe and gm of PNP AND NPN must
also be considered.
The huge amount of NFB reduces the device differences enormously.
see
http://en.wikipedia.org/wiki/Sziklai_pair
Many amps have PNP and NPN devices in an output stage, and the match
between them is
often very poor indeed, like having an EL34 and a 6L6 in a PP tube amp.
Most ppl wouldn't notice any difference though as the resulting increase
in THD
is marginal only if they are biased at the same idle current.
Its extremely easy to build an emitter follower complementary pair
output stage using NPN and PNP
devices and find that distortion WITHOUT ANY OTHER LOOP OR GLOBAL NFB
becomes inaudible.
This is because the follower connection is an application of about
30 to 40 dB of local series voltage NFB, and the open loop operation of
the same transistors in common
emitter mode, ie, with load in the collector circuit would generate
perhaps 10% THD at clip, and maybe 2% crossover artifacts at low 2 watt
levels,
so when 40dB of follower FB is applied, the 2% becomes 0.02%.
The ME design using Sziclai has a lot of NFB.
It is somewhat similar in principle to
http://www.ampslab.com/c200cfp.htm
In adhering to a 30 year old design Peter Stein lacks any flexability
or fluency in ability to design something different.
The Sziclai isn't especially wonderful, just another of many ways to
hook
up a bunch of transistors.
Matching helps minimise distortions, but only very slightly.
Trevor would have to move mountains to prove otherwise.
see also
http://pirun.ku.ac.th/~fscinrn/Nuclear%20Instrument/node97.html
NEVER BUY ME AMPLIFIERS. THERE ARE NO SERVICE MANUALS.
Patrick Turner.
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