Re: Class D! OT but interesting
- From: Patrick Turner <info@xxxxxxxxxxxxxxxxxx>
- Date: Wed, 13 Feb 2008 13:26:28 GMT
Engineer wrote:
Hi, Vacuumlanders.
I just read this in IEEE Specturm magazine.
http://www.spectrum.ieee.org/feb08/5953
It's about a Belgium chap, Bruno Putzeys, who designs state-of-the art
Class-D amplifiers - that's solid state switchers for the uninitiated.
I have long recognized that a solid state unit can be a better "short,
thick wire with gain" delivering "any" current at "any" voltage at
"any" frequency into "any" speaker load at "zero" distortion (OK, some
hyperbolae here!) than a tube amplifier. However, I've always felt
that the epitome of the solid-state power stage was the big linear P-P
MOSFET. Thus, I've never liked Class-D audio. But I may have to revise
my prejudices!
There are two short reference to tube audio in the article. One
states that the Bruno's latest Class-D amplfier has "30,000 times less
distortion than some (sic) tube amplifiers". OK, that "some" hides a
lot... An 50C5 O/P stage in an "AA5" AC/DC radio receiver may have
10% THD at at 2 watts (or less)... Unfair reference, any decent tube
amp can beat 0.1% easily. Hmmm, I'd settle for 30,000 times less than
10%, or 0.00033% THD. Indeed, the figure given is 0.0003% at 20 KHz
at "full power" - the latter not defined but presumable at least 20
watts/ch, likely more.
So, read and enjoy. I'll stick to tubes for the fun, the "hands-
on" (anything can be fixed), the rosy glow and the overall vintage
aura. Oh, and for serious listening? (That's classical piano for me.)
A 40 lb, over 100 wpc linear S/S stereo unit and a pair of Ditton
442's... don't shoot! <g>
Cheers,
Roger
Ci Audio also makes little 100W mono amps in 6 inch sided cubes with no
HS, because they
are 95% efficient.
Chi uses toroidal PT and linear PS and the circuit module that accepts
the digital or analog inputs
is the size of a matchbox, and is un-repairable if it goes wrong.
I compared the sound of the Ci Audio to other SS generic amps and
couldn't hear any differences
so most folks will accept "digital" amps without knowing WTF is in the
box because as long
as it works to amplify their MP3, its all OK.
This will make all class AB analog SS amps into dinosaurs soon and
do wonders for lowering greenhouse gas emmisions.
Tubes will remain, and be used by a small minority of outlaws and
rebels,
but compensated for by the huge overall greenhouse reduction by dumping
all those hundreds of old Krells,
Gryphons, and other humumgous SS amps, and millions of generic AB
cheapies.
Someone did digital pulse width modulation with tubes for a power amp
once.....
The OPT does not have to be so big and heavy.
The PWM technique was used first with tubes I think for FM detection in
the 1950s....
Patrick Turner.
.
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- Class D! OT but interesting
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