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What are the advantages to a Class A amp & what are the trade offs?

I've never had a class a amp but am considering one now. So what am I getting myself into?
128x128artemus_5
bdp24's avatar
bdp24
9,788 posts
 

There is one maker of a well-regarded tube power amp (I’ll allow he and it to remain anonymous, so as to not appear to be "pushing" them) who offers the amp in both Class-A/B form, and in pure Class-A. Both versions share the same circuit architecture, power supply, tube compliment, etc, differing only in the biasing required to create each version.

The A/B version produces 100w into 4 and 8 ohms, the A version 40w. So why would anyone go with the 40w version? The designer claims (and there’s no reason to doubt him, at least in my mind) the Class-A version produces 1/10th the distortion of the A/B version. How audible is a tenfold decrease in measured distortion? I can’t answer that question.

artemus_5's avatar
artemus_5 OP
1,927 posts
 
@bdp24 
I learned long ago that the low powered amps sound better to me. I've had amps for 35wpc to 250 wpc. The 35wpc sounds best in my system. Unless one is pushing an 84db speaker load, high wattage is not needed. Even then, the low power may work. The amp I am considering is 40wpc and has pushed the 84db speakers
bigkidz
3,381 posts
 

I recently built a Class A 35wpc power amp based on the First Watt design.  The Class A was much better but I also use the best parts available and point-to-point wiring.  I also recently upgraded a few Counterpoint hybrid power amps with bipolar transistors with Class A output and the difference was much better. It added more clarity, depth, dimension and faster dynamics. You have to try them out for yourself as always.  I agree with the posts above mine.


Happy Listening.

koestner
667 posts
 
Class A amps are like driving your car around with the gas pedal floored, and controlling your speed with the brakes. It is a rather inefficient method.
8th-note
407 posts
 
The class of the amp is only one criteria on which to make a buying decision. I have a mid 90's Krell KSA 300S that I dearly love but the Class A feature has its downsides. It weighs 185 lbs. and it runs so hot when I play it loud that I can't touch it. But it puts out 1200 watts at 2 ohms and it sounds gorgeous. It's a perfect match for my speakers (Mirage M3si) which are very low sensitivity (I routinely drive the amp into the highest bias level). This amp is a technology statement and there are very few new amps which can match it's performance, at least for under $50k. I am willing to live with the downsides of this amp because I admire the design philosophy and it sounds very good to me. It's kind of like owning a vintage Porsche that isn't very practical but it's just so fun to drive.

The Canary is a very different animal than the Krell but If the M70 flicks your Bic go for it but understand that the Class A feature is only one aspect of the amp.
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