What could I expect to hear from a Class A amp?

For further and deeper understanding of Class A design and operation visit http://passlabs.com/articles.htm There you can find several articles dealing with Class A and other amplification devices. Well worth the time to visit and read the articles from the man that for all practical purposes responsible for and defined high end in the mid 70s to today.

Nelson Pass when he was at Threshold clearly defined and manufactured some of the worlds best Class A amps and preamps. In 1991 he left Threshold and started Pass Labs and the in the years since these products have further pushed the envelope of Class A design. In my opinion no one does it better than Nelson Pass.

Over the course of 50 years in this hobby have heard or owned or near owned damn near all the high end amplifiers produced. Such as Levinson, Threshold, Krell, Classe, Coda and many others to numerous to menetion here. But when it comes to Class A ampd I have always gravitated back to the Nelson Pass Threshold and Pass Labs units. At present I do not have a Pass unit in the system. Moving shortly to the X350.5 in a few months. Now running a PS Audio HCA 2 Class D amp. Very happy with it, but no where near the level of the X350.5 While it is not a pure class A amp such as the Aleph series, it delivers the signature I want, with less heat and drain on the power bill.

As far as Levinson and Krell go I have never kept any of them longer than 3 months. Impressive at first, but in the long run just have not pleased my ear.

As far as tubes go, when I got into this hobby that was all there was and mono to boot. So from 1957 to 1977 was in the tube camp until the Threshold gear came out. Dumped the tube gear in 1977 and haven't looked back. Twenty years of fiddling with tube gear was entirely enough for me. And that was during a time when you could buy new good tubes made in U.S. or great tubes from Europe. I have heard the Russian and Chinese tubes, to me pure junk as opposed to what we had in the tube era.

One of the great Class A/AB amplifiers I have heard recently was the Musical Design D150B signature unit. Now thats one Class A/AB amps I could live with nicely and totally recommend.

Class D amp have miles to go, to even be remotley considered in the realm of pure Class A amps. Even with the attendent penalities of Class A operation of high cost, high heat, heavy chassis, the need to be powered 24/7, additional usage of power to your monthly bill. Even with that all against Class A amplifiers, once you hear and become accustom to the signature of Class A, there is no turning back.

I myself at the moment using a Class D amp in the PS Audio HCA 2 which I would never compare to a properly made Class A amp. While close, it is no cigar. No doubt that Class D will evolve in years to come, but not just yet. I have listen to the Rowland, Channel Island, Nu Force as well as the PS Audio I have here. The only Class D amp that comes close enough to warrant a close examination is the Rowland.

The rest are nothing more or less than contenders at this point in time.

Class A amps should run 24/7 for maximum thermal efficiency. By turning them on and off shortens the operational life considerably due to convection. In a way its like a light bulb turn on and leave it on it will damn near last forever as opposed to the constant on/off cycle.

One of the reasons for listener fatique is due in part to the on/off cycle. Run it for a solid week of 24 hour operation and you will hear the difference and the difference you paid for a Class A amp.

In fact I run my all my amps regardless of Class of operation 24/7. They just sound better by being continually on. Many of the newer amps have a standby feature which allows to the unit to stay on, but at a less power consumption.

Obviously say a Class A amp running at 60 WRMS per channel, if its pure Class A it is drawing 300 Watts at the wall. Something to consider in regards to your monthly power bill.

There are trade offs in using Pure Class A amps, but over the years I have found, for me it is well worth the penalties that come with Class A operation.

Coda makes some very good Class A amps in pure Class A and biased Class A. Recently heard the Coda S5.5 a real stunner. Also if you can find the Coda 12.0 it is a heavy contender in Class A amps.

Most of the Coda staff is former Threshold staffers, that formed their own company. So the Pass legacy is clearly evident in their product line.