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How could 100 Watt class a has more head room than a 300 Watt amp Class AB

Put aside which brand or make.
I put two amps into a test, both highend amp came from the same manufacturer.
Both double down the power with half of the impedance load, and THD is about the same.
Regardless of the size and cost difference, from a pure science perspective.
300 watt in theory should provide more headroom and sound ease when it reaches 100db, but the reverse is the true, the class A 100 watt seems to provide more headroom.
I have tried to use another set of speakers which is much easier to drive and it reaches the same conclusion.
Can someone explain why?
Quality or quantity of watt, how do we determined?
samnetw

Showing 4 responses by georgehifi

georgehifi's avatar
georgehifi
10,312 posts
 
From the Stereophile XA60 review it'll do 130 watts into 8 ohms and keep going up as the impedance is lowered.

130W into 8 ohms 
210W into 4 ohms
330W into 2 ohms

It's no wattage doubler as you can see from the Stereophile tests, but it at least it keeps going up, some like many Class-D's just s**t themselves into 2ohms, and can't get much above the 8ohm watts.

Cheers George 
georgehifi's avatar
georgehifi
10,312 posts
 
A Class A single ended amp gets rid of whatever crossover distortion might exist in push pull circuits so there’s that, and when exposed to this phenomena the listener is rendered a better person almost instantly.
+1 for that, and that’s any class-a not just SE.
Ever listen to a pair of old ML-2’s in good working condition through good ESL’s with maybe dynamic bass like Monoliths, MAJESTIC!!!!!! So long as you don’t want party levels.
This amp keeps doubling down to 1ohm, I’ve seen it do it on the bench.
Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 

Take this into account, at normal moderate listen levels, a pair of Mark Levinson ML2 (BJT) monoblocks are only 25w @ 8ohms, but they will out perform things like a Perreaux 3150 300w @ 8ohm (Mosfet) into hard to drive speakers, because the ML can deliver more current into that harder load, where the Perraux will start to compress.

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 
How could 100 Watt class a has more head room than a 300 Watt amp Class AB

If one were a Mosfet output and the other a BJT (bi-polar) and both were well engineered push/pull and driving into a heavy load, such as the Wilson Alexia which has an EPDR (equivalent peak dissipation resistance) of just .9ohm!!!! at 65hz.
Then the 100w BJT amp would drive it better than the 300w Mosfet.
As the 100w BJT "could" in effect give out 800w into that .9ohm load where the Mosfet would probably go down to less than it’s rated 8ohm 300w output.
Cheers George
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