Pooh Bear said:

To illustrate that a tube produces distortion, all you need to do is to look at the
transfer characteristic. No tube has a truly linear 'curve' .... ahem - hence they
are called curves it seems - lol.

Ahem........let's put some nuances into this picture.
Look at the "curves"of a BJT, a JFET, a MOSFET, a triode and a
pentode.
ALL of them are non-linear.
Tubes are somewhat quadratic, BJTs have an exponential curve.

The best part is that triodes have the most linear and long Ia/-Vg
curve of all devices.
Besides, no one is so naive to use a bare device, there's always some
feedback involved, be it locally or globally.

The fun part is that tubes with little LOCAL feedback don't
necessarily need global feedback to rely on for relatively
distortion-free transfer of audio signals.
Transistors, and especially BJTs, do need heavy doses of it to just
function as proper amplifiers .

As you probably know, the use of SS and GNFB can add distortions that
have little or no relation to the input signal. The spectrum of the
distortion alters.
Of course, local feedback in SS stages (e.g. emitter degeneration in
differential amplifiers) may solve most of these problems, but the
mostly very high common mode signal may still pose problems.
HF interference is another subject. FTZ and NP0 don't solve this
altogether. EMC is a serious problem ( and business) these days.

This is something I rarely see in consumer audio applications however.

Then there's something like "thermal distortion", variable junction
capacitances etc.

Of course, this is a very simple approach of a subject where one could
fill thousands of MBs with and still not be complete.

May I refer you to the work of Matti Otala, Artur Seibt, Jean Hiraga,
Kaneda-san and Peter Garde for instance? A very interesting read,
note.

If you're in for an in-depth discussion of these matters, wait until
Sunday, then I'll have an entire day to discuss this and related
subjects.

I'd be delighted to do so.
Just let me know, and I'll start a separate thread with this subject
here in RAO. Maybe RATech too, as there are some sharp minds wandering
around there as well.

--
Sander deWaal
"SOA of a KT88? Sufficient."

"Sander deWaal" wrote in message


Pooh Bear said:

To illustrate that a tube produces distortion, all you need to do is
to look at the transfer characteristic. No tube has a truly linear
'curve' .... ahem - hence they are called curves it seems - lol.

Ahem........let's put some nuances into this picture.
Look at the "curves"of a BJT, a JFET, a MOSFET, a triode and a
pentode.

ALL of them are non-linear.

It's a matter of degree, right?

Tubes are somewhat quadratic, BJTs have an exponential curve.

Last time I looked the plate curves of a triode, tetrode and pentode were
way different from each other. How can they all be quadratic?

The best part is that triodes have the most linear and long Ia/-Vg
curve of all devices.

If that's true why does tubed equipment have so much more distortion than
SS, as a rule?

Besides, no one is so naive to use a bare device, there's always some
feedback involved, be it locally or globally.

OK, so there's nothing necessarily wrong with inverse feedback, right?

The fun part is that tubes with little LOCAL feedback don't
necessarily need global feedback to rely on for relatively
distortion-free transfer of audio signals.

How does that fit with the fact that just about every tubed high fidelity
preamp and amplifier has global feedback. I've seen shematic diagrams for WE
amps going back to the 1930s, and they had global feedback as well.

Transistors, and especially BJTs, do need heavy doses of it to just
function as proper amplifiers .

Nope. They do well with local feedback, as well.

As you probably know, the use of SS and GNFB can add distortions that
have little or no relation to the input signal. The spectrum of the
distortion alters.

SS equipment as a rule has an order or two less distortion than comparable
tubed equipment. Therefore, the spectrum of the distortion is irrelevant
since there is so much less of it.

Of course, local feedback in SS stages (e.g. emitter degeneration in
differential amplifiers) may solve most of these problems, but the
mostly very high common mode signal may still pose problems.

Please define common mode signal in this context.

HF interference is another subject. FTZ and NP0 don't solve this
altogether. EMC is a serious problem ( and business) these days.

Certainly not a problem for SS that hasn't been abundantly solved, many
times.

This is something I rarely see in consumer audio applications however.

Then there's something like "thermal distortion", variable junction
capacitances etc.

If that's true why does tubed equipment have so much more distortion than
SS, as a rule?

And if capacitances in transistors are such a problem, why is it that
microwave signal-handeling equipment is typically SS.

Of course, this is a very simple approach of a subject where one could
fill thousands of MBs with and still not be complete.

If tubes are so superiorwhy does tubed equipment have so much more noise and
distortion than SS, as a rule?

May I refer you to the work of Matti Otala, Artur Seibt, Jean Hiraga,
Kaneda-san and Peter Garde for instance? A very interesting read,
note.

I'll bet I've read more of them than you have, Sander by far. I have the
complete archive of the AES on my hard drive.