First foray into Class A amp -- recommendations

Mtrot, Hi, I own the 700cx modded, There is a huge substantial difference between this and the 300cx you are looking at, if my amp was not modded, there would still be a big difference, for one, the 300cx is the bottom of the cx line, and the 700cx is the top of the stereo line, which esentially is mono blocks in one chassis, where the 400cx and 300cx is not!, hope this helps, Happy listening.

If you have cold winters, than KSA200 is able to provide heat to the whole room.

@Zd, fair enough. I certainly wasn't criticizing Class A power as my Vitus runs in pure class A up to 25 watts true rms and can be manually switched to class A/B mode which delivers 100 watts true rms and is great for home theater duties. In Kl.A mode the Vitus can change to Kl.A/B mode at very high volume levels or under extreme load, but does so instantly without switching. That is what I meant by pure Kl.A. The Krell fanbois endlessly claim that their amps are pure Kl.A, when in fact they use a sliding bias scheme as confirmed by John Atkinson. Only a few pure class A amps have been built, including the Threshold T800 but they were prone to failure.

What I meant is, most customers want the marketing bs and claim they do not. Amps like Boulder and Rowland market Class A amps which in reality are highly biased class A/B amps. Vitus do not change the bias based on input signal amplitude – that has nothing to do with real kl. A. It's just a marketing gimmick. What Vitus's research has shown is that when the transistors they use has a core temperature of about 70degrees C then the music becomes REAL Liquid – listenable for hours – not the usual competitor “bleeding” ears after 30min. Some call it dynamics, “air” in the high freq – I call it a headache.

Moreover a lot of manufacturers routinely quote peak power figures, or don't quote "true RMS" power just to impress people. Vitus quote their power figures in "true RMS" which is a correct, but less impressive spec. Also, Vitus is using in-house designed UI-core transformers which are much more efficient than typical toroids used by most manufacturers and loses max 1.5v tested. That is another reason why specs on paper mean very little.

If you really want to discover Class A amps, the Krell KSA amps might not be optimal. They're very good amps IMO and I owned a KSA 50s for many years, however these were sliding bias designs that went to A/B operation when necessary. That's not a bad thing per se, but its not an ideal choice if you're looking for a pure Class A amp. OTOH.......

A pair of used Clayton M100s would be worth considering if a pair pops up. The last ones I recall seeing on Audiogon went for $3k ish - some time ago - so they should be near your price point. Their small, deep chassis might make it easier for you to accommodate mono amps, too. The Clayton amps were real Class A monsters and could roast meat as well as handle tough speaker loads. IIRC, the M100 was the smallest mono amp Clayton sold and put out 100+ watts in Class A.

I'm not sure how much benefit Class A amps provide into any given speaker, but this one will allow you to find out.

 

I ended up buying a Krell FPB 400cx and the sound has been great.  I have had it plugged into a regular 15 amp outlet and I'm about to have a couple of dedicated 20 amp lines run, just to make sure it has enough "juice".