[Arny Krueger]

"Eeyore" wrote in
message
Arny Krueger wrote:

"Eeyore" wrote:
Arny Krueger wrote:

For one thing, modern output transistors have Ft up in
the megahertz range. Back in the 70s people were still
struggling with output devices with Ft in the KHz
range.

Has no influence on the change in transconductance of
output devices with load current.

But it does have something to do with the shape of such
transients as show up when you there is some crossover
distortion.

Not directly. The open-loop bandwidth of the amplifier
(which can be higher with modern high fT devices) does
that. The larger bandwidth means more NFB can be applied
at the higher audio frequencies which in turn reduces the
level of the high harmonic order THD products.

You COULD build an indifferent amplifier design with high
fT devices and not get that benefit you see.


But thanks for bringing up the issue of change in
transconductance of the output devices, particularly at
low current levels. That's another issue that modern
devices sometimes do better at.

I doubt that it'll be much different. It's the basic
device physics you see. You can reduce the impact by
cleverer design though.


Stop talking irrelevant nonsense.

Lighten up, Graham. So seem to forget about all the
truely weird nonsense that we see on Usenet. How long
has it been since you were on AAPLS?

I expect better from you.

You're getting it. Most of AAPLS stop thinking about the time you say
transconductance., if not well before.

How many amplifiers have YOU designed btw ?

More than I'd care to admit here. The experience made me
a believer in commercial amps. :-(

It's like what Scott said in a recent post - relying on people who do
something better than you.

My amp designs in the mid 80s (???) got to the point where there I was kinda
stopped at 0.03% THD at full power at 20 KHz, and less than that at all
frequencies and power levels below that with excellent stability into just
about any load. I wanted better, if I was going to bother building any of
them up into a finished component. The DH 200 did better than that, and if
my amp couldn't whip a DH 200, why bother?

You're aware that I've designed a fair number of
successful commercial designs I believe.

Yes, but you seem to be very worried about things that just don't happen
with the modern SS amps I've tested, even fairly rugged cheap locomotives
like the QSC USA series.