"flipper" wrote in message
...
On Thu, 29 May 2008 09:56:14 +1000, "Trevor Wilson"
wrote:
"flipper" wrote in message
. ..
On Thu, 29 May 2008 09:01:52 +1000, "Trevor Wilson"
wrote:
"Ian Thompson-Bell" wrote in message
...
wrote:
"In a word: YES...
"The answer is rooted in the harmonic content that the device can
pass
or generate..."
Continued: http://easyurl.net/TubesTubes
There is a lot missing from this article. First, it is triodes alone
that
generate pleasing 2nd harmonic distortion. Pentodes generate odd
harmonics
just as much as transistors do.
**So much nonsense, so little time to correct it. Why this myth
continues
to
be perpetrated is a complete mystery. The TOPOLOGY dictates what type
of
harmonics are generated, not the devices.
Well, you're half right. They both dictate the harmonics.
**I am 100% correct.
No, you're not.
Topology is the factor.
It's one factor.
**It is, by far, the major factor. It swamps any influences by the output
devices. Take away global NFB, for instance, and differences between devices
is more readily apparent.
Not the devices.
B.S.
**Keep dissagreeing all you wish. You'll still be wrong.
Of course,
various devices DO contribute different distortion amounts.
And different harmonic distributions as well.
**All of which is swamped by topology differences.
For instance:
* At low bias currents, pentodes add large amounts of distortion.
* At low bias current, triodes add smaller amounts of distortion.
* At low bias currents, MOSFETs add very large amounts of distortion.
* At low bias currents, BJTs add smaller amounts of distortion.
Push pull eliminates even order
distortion products. Valve or solid state.
But does nothing for the odd orders, which are dictated by the
devices.
**Sure. ALL amplifiying devices add odd order distortion.
Yes, but with different distributions.
**All of which is swamped by different topologies.
At moderate bias
currents, the approximate order is (from best to worst):
BJTs
Triodes
Pentodes
MOSFETs
At high bias currents, the order shifts somewhat to:
BJTs
MOSFETs
Triodes
Pentodes
Except for BJTs being the worst of the lot under all conditions that's
not too terribly screwed up.
**Wrong. Modern BJTs are, by far, the most linear output devices available.
Look at the Hfe vs. Ic curve of this device:
http://www.datasheetcatalog.org/data...shiba/3228.pdf
A VERY linear (low distortion) device over a very wide range of currents.
It's PNP complement is similarly low distortion.
It is the TOPOLOGY which dominates the issue of distortion production,
however.
Wrong.
**Don't be silly. Compare SE to PP. Compare zero global NFB to high global
NFB topologies.
Depending on the amount of feedback employed, the devices used
makes little difference.
Also wrong.
**Here's where I get to say: PROVE IT.
--
Trevor Wilson
www.rageaudio.com.au