Yep, my 25W Class A monoblocks, dissipate 400W when idling, weigh 30Kg each, are about a cubic foot in volume and run so hot I can't use them in the summer.
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So I did a bit of reading on the subject. Krell claims that the FPB amps can deliver Class A power to its full rating. Due to a process called Sustained Plateau Bias II it raises and lowers the bias as demand dictates. Of course this is what Krell has to say in the owner's manual.
In practice, it does an amazing job of performing this function. A Google search on sustained plateau bias 2 brings up much interesting reading. And I found one article where the writer performed some tests on my exact amp, which makes it all the more interesting for me anyway.
http://audioinvestigations.blogspot....teau-bias.html
Some mumbo jumbo about what he measured as he pushed the amp. It seems it has about 4 levels of bias it jumps back and forth between as required. Keeping it in Class A at all times. Well all times except if it runs hot. If the amp gets too hot, it will lower the bias level and let it run into A/B to keep the temp within safe parameters. Or if it runs out of current. So, that brings up many variables. Speaker load, current demands, room temp, and the volume you are trying to achieve, and others. But, if your speakers present an easy load, and your room is cool, and you aren't trying to break the windows, it should remain in Class A pretty much all the time.
If you really want to get into some heady reading, I read most of this:
https://books.google.com/books?id=7d...s%20II&f=false
That really takes me back to my college days. Great stuff if you're having trouble sleeping. And there was a whole page on Google on the subject, if anyone was interested enough to read it all. But these modern designs allow us to have large class A amps that would have been cost and weight prohibitive in the past. Not that a $10k amp that weighs 130lbs is practical.
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My MF A1000 was supposedly class A all the way. It certainly got damn hot and had a lot of cooling fins.
My wife says I'm Class A and I'm definitely hot all the time 😊
But I might be biased 😂
That was what they said re it... 16 output transistors.. specs were
Power output : 2x 50W (Class A, 8 Ohm)
MC input : 600µV
MM input : 8mV
Line inputs : 350mV
S/N ratio : > 60dB (MC)
> 75dB (MM)
> 85dB (lines)
RIAA accuracy : ±0,7dB
THD : < 0,5% (20Hz...20Khz)
Channel separation : > 85dB
PC : 215W continuous
Dimensions : 48,3 x 12,2 x 33,5cm (A1000)
19,4 x 12,2 x 33,5cm (PSU)
Weight : 11kg (A1000)
7kg (PSU)
I would expect that these give class A into 4R, 50W, if they dissipate that much! Nice!
If an amp is specified as say 20W into 8R, class A, then it will only give 10W class A into 4R.... it may well double its power to 40W yes, but only the first 10W will now be in class A. I suspect Barry's amp is biased at probably double the class A current actually needed to give 25W. This is excellent but not cheap!! This means that when the amp is close to voltage clipping into 8R (at 25W) it is still nowhere near to coming out of class A;)
Sounded bloody marvellous and I really should have kept it
http://www.thevintageknob.org/museum...30&t=0&s=1&n=1
http://www.thevintageknob.org/museum...30&t=0&s=1&n=2
http://hifisale.narod.ru/_si/0/10714081.jpg