Should I buy a Class A Amp.

Most Pass Labs amps are also high biased A/B amps, and yes if you were to play a piece of music that was very mellow like slow blues, some Class A/B amps may stay in Class A. But maybe with a full blown orchestra that same amp may go into class B.
Also an A/B amp may stay in Class A  if the speakers impedance stays at say 8ohms, but if that same speaker dips to 1,2,,3 or 4ohms somewhere in it's impedance curve then that same amp may go into class b.

Cheers George      

All high bias Class A/B I think except for an early massive Gryphon which was suppose to be pure class A to clipping into 8ohms.

You just have to look at the old huge ML25 monoblocks which were 25w pure class A only into 8ohms. The heat factor goes up exponentially the more watts there are, because the rail volts have be to increased.

So for two amps, one 20w class A that’s all.
And the other 100watts class A/B still with only 20w of Class A bias, this amp will be 4 x hotter. Even though their both only 20w Class A.
This is why I had to water cool the amp I made 4 posts back because I wanted 150w and Class A all the way.
Cheers George

The 300 series ML’s are high biased class A/B, B after the bias runs out, they are not pure Class A.
Looking at the heatsinks I say about 20-30w Class A bias max, as Stereophile also said they weren’t too hot to touch, even after 1 hour pre-conditioning at 1/3rd power.
If they were pure Class A they’d be the size of a very large coffee table with heatsinks big enough to warm the whole neighborhood.

Stereophile full power tests on the No.334 are at 1% THD!!!.
8ohm = 139.9w
4ohm = 243w
2ohm = 430w

Bottom of the page measurement chart
http://www.stereophile.com/content/mark-levinson-no334-power-amplifier-measurements-page-3#toJJo0Xxp6m0aqe4.97

Cheers George

After 20 years of use even though all metal parts were aluminium, electrolysis started, it started to get corrosion, it was getting dangerous, so I rebuilt it into a normal big amp with big heat sinks hi bias first 30w Class A  and sold it.

Cheers George

inna2,067 posts07-19-2016 7:39amWhy would class A operation make an amp slower? Is it inherent in the design? I don’t understand these things.
Another question is is the full class A amp a simpler design that just has to be executed well to make sense?

Class A done right will not be slower, some say this, but it’s just poor design eg: power supply not being up to constant draw on it etc.

And no, a proper designed Class A is more complex, re heat power supply etc.

OK a bit of why I love Class A so much.
I built a pure class A 150w back in the 70’s a three man lift (best amp I or anyone ever heard nothing came close to it) so easy to listen to, huge dynamics, massive sound stage, pinpoint image with depth. But the dynamics were not in a forced way that shot out from the individual drivers, but in whole envelopling way, that washed over you, with it’s bigness and dynamics

But this amp had a 2 x 5kva transformers with 220,000uf capcitance per channel, 18 per channel for memory Hirel EB203 ED204 tranistors, and the big one the whole heatsink was water cooled with it’s own small radiator, variable speed radiator fan and silent water pump to keep the output transistors heat stable,

This amp drove a mates double stacked quad ESL57’s with Decca Kelly ribbons from 10khz up, two x 24" Hartley woofers mounted in the back brick wall, using the next room as the speaker box. The sound was sublime.

The sources were Linn LP12 Black Widow arm and a Stax electrostatic cartridge, that need to be tuned in with it’s own tube supply and scope that took 1/2hr but only stayed in tune for around 1hr before needing to be re-tuned again because humidity changes. We fed that into the amp via my first MkI Lightspeed passive pre.

If you can find them the Mark Levinson ML2 monoblocks are massive but only put out 25w pure class A
They will drive any nasty speaker load, but the speaker has to be reasonably high in efficiency, eg > say 88dB
 


Cheers George

inna2,069 posts07-19-2016 11:09amGeorge, thank you.
Would you some people mind writing in normal English?

Sorry inna, that was more for the techs here, who want to know why I’m in favour of well designed Class A amps

BTW: I noticed my link to the Mark Levinson ML2  25w Class A mono block beasts didn’t take here it is.
http://www.highendclassics.com/brands/marklevinsonml2-2

Cheers George

Is Class A the best design? Look at it this way: no preamplifier designer would ever build anything other than Class A.

This statement says it all, if a preamp was a/b it wouldn’t sound very good, all decent preamps are class A.

It’s the same for Class A amps even more so, but you have to cop the negatives, heat, powersupply ability, size, weight, and power consumption.
All these negatives have nothing to do with poor sound quality, if fact it’s the opposite, Class A done "right" is superior to any a/b, b, d, h etc etc

Cheers George

donplatt

Hi, although I like Krells very much there were only two that were real Class A the other were either "high" biased into Class A or sliding (plataue) bias types.
These two Krell that were real Class A were the ones that were fan forced cooled (no heatsinks on the outside) and were the KSA-50 and KSA-100 which may have come as monoblock form as well.

http://www.stereophile.com/solidpoweramps/985krell/#wCIDLgktMRqomRuM.97

http://img.canuckaudiomart.com/uploads/large/853586-krell-ksa-100-mk2-completely-rebuilt.jpg

Cheers George 

Once you've lived with a "good" pure Class A solid state amp it's hard to go back even to a highly biased Class A a/b amp.
The sound just seems to envelop you from speakers with an ease, without being drawn to them, that the sound is coming from elsewhere in the sound stage rather than emanating from them.

Cheers George