CLASS A AMPLIFIERS

Unsound,

You can also check out the reviews by Stereophile, such as
Martin Collums April 1997 review of the then current FPB-600.

http://stereophile.com/amplificationreviews/829/

In the Measurements segment, Martin addresses the power that
the amp can deliver into low impedances:

http://stereophile.com/amplificationreviews/829/index8.html

"I wasn't able to run my long-term continuous testing at
2 ohms, but compromised with five-second bursts-long by
peak-measurement practice (eg, 20ms). The FPB 600 could
sustain a 29.3dBW level into this load, corresponding to
3.4kWpc-an extraordinary figure."

Dr. Gregory Greenman
Physicist

Unless I missed something, everything in these aritcles suggest that the Krell's are capable of maintaining Class A operation as they double down, but, they don't actually make that claim. As for me, I believe they do. Wretched excess? I love it! I may be part of the minority here on Audiogon, but I really like the "real" Krells and thats based on what I've heard not on what I've read. Though it is pretty impressive reading.

Unsound,

The circuit topology of the Krell FPB series is Class A.

Class A amps don't automatically resort to A/B when they
are asked to output large amounts of power.

No - that is a characteristic of Class A/B amps that are
designed to maintain Class A at low levels - and then they
revert to what they really are Class A/B.

However, a true Class A like the Krells doesn't automatically
revert to A/B at high levels.

Dr. Gregory Greenman
Physicist

Moribus, thank you. That really clarifies it. Am I correct in assuming that power increases by ss amps into lower impedances is not determined by Class of operation?

What caught my eye in the Stereophile measurements was paragraph 3 where they state it's a 935 watt amp continuous, almost 30db. It doesn't put out 1870 wpc into 4 ohm or 3740 into 2 ohms continuous. "However at it's rated power of 600 wpc, which is 28 db, it would hold that rating for all loads from 8 to 2 ohms". I read about many an amp that put out 100 into 8 and 150 into 4. What if that manufacturer decided to rate it at 75 into 8, even though it put out 100? Then he could say it "doubled down" to 150 into 4. Impressive little amp then. Nobody is going to sue anybody if they buy a 75 or 600 watt amp and it puts out 100 or 935 respectively. Gee, I got more than I paid for. But it's the wordage I look at. Doubles its "rated" power is honest but to me, it is what it is, and if its "really" a say 250 watt guy, I'd be curious how close it came to 500 into 4 but most important is how it sounds into 4 or 2 ohms. Some amps start to get a little unhappy down there. If it makes someone happy to believe their amp doubles down that's fine but I don't listen to specs so my criteria is just "does it draw me in".