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Old 15th March 2002, 12:33 AM   #1
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Question Officially Class A

I just bought anX150 for my Apogee Duetta Signatures. A buddy bought a Llano Trinity 200 (200 watts/side) the same time. At an apogee site <http://audioworld.com/cgibin/sw/foru...Group&number=1> there has been an ongoing hot discussion whether the Llano is truly Class A throughout its rated power using moderate heat sinks that don't get hot. Randy White, the designer insists it is. After a phone conversation with Randy, one member came back with this to report:
Just got off the phone with Randy White. His amps run pure class A to rated power. They run cooler because the new MOSFETs he is using have a much lower impedence than usual. Even so the Amp idles at 300watts/Ch. The Trinity 200 that is. These Amps have an efficiency of 66% at full power. Not bad at all. Of course it stinks at Idle but what the hey, how many of us listen at Idle.

What say you?
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Old 15th March 2002, 01:21 AM   #2
grataku is offline grataku  United States
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me sez,
now I know why I don't hang @audioworld.com.

66% eff. is too high for class A.
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Old 15th March 2002, 01:38 AM   #3
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unless of course it uses dynamic bias.....

my guess, It aint class A @ rated output.
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Old 15th March 2002, 01:44 AM   #4
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Quote:
Originally posted by AudioFreak
unless of course it uses dynamic bias.....

my guess, It aint class A @ rated output.
This increases efficiency, but nowhere up to 60%! I agree, it's probably class A at lower output levels and AB at full output.
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Old 15th March 2002, 02:16 AM   #5
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What about Randy White's assertion that highly efficient Mosfets are largely responsible for the Class A rating?
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Old 15th March 2002, 02:34 AM   #6
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Quote:
Originally posted by Lisandro_P


This increases efficiency, but nowhere up to 60%! I agree, it's probably class A at lower output levels and AB at full output.
Well push pull can be just under 50% so i wouldnt right it off totally.

Quote:
Originally posted by muralman1
What about Randy White's assertion that highly efficient Mosfets are largely responsible for the Class A rating?
Has almost nothing 2 do with it sorry. Pure Constant Bias Class A cannot be over 50%.

I guess althought unlikely, it's also possible Randy's amp uses a tracking power supply.
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Old 15th March 2002, 04:36 AM   #7
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50% is the theoretical maximum. But i dunno, actually i never got to think how much the dynamic bias thing improves efficiency, though i'm almost sure it's not 10%.

A schematic for that amp would be nice... anyone?
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Old 15th March 2002, 04:55 AM   #8
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The lower impedance of the FETs has nothing to do with the amount of heat dissipated in a class A or class AB amplifier. It's only marginally meaningful in switching class D types.

Even if you meant "thermal" impedance. The answer is the same. Hogwash!

If dynamic biasing is used, then it is possible to achieve higher efficiency, but FET impedance is irrelevant.

Jim Hagerman
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Old 15th March 2002, 04:09 PM   #9
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You can take a look at the Trinity 200 at:

http://www.whiteaudio.com/page2.html

I will be listening to the Trinity in comparison with my Pass at my place very soon. I will post my findings.
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Old 15th March 2002, 08:33 PM   #10
grataku is offline grataku  United States
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Muralman,
don't bother. Noboby here cares.
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