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Class A Power Amp Degredation

Dear Forum Members,

I've read in several places that because class A amplifiers run hard all the time and most people don't cut them off, they wear our faster. Plus, because they remain on all the time they burn much more electricity and generate lots of heat, some more than others, at least that's what I'm told. I wonder what happens if I have to go away for a day or two?

I can't afford to purchase a brand new class A amp so I wonder if I should even consider the purchase of a used Mark Levinson, Pass Labs or other class A amp? The only amplifier I know of that can be switched between class A and A/B is the Plnius. I am told that this amp only run very hot when it's running in class A.

Here are my questions:

1. What should I look for in a used amplifier?
2. Do class A amps wear out faster than other amps?
3. Are there amplifiers that can match the musicality, sound staging, bass and sweet sounds of a class A amp? In other words are there any class A/B amps that have all of the quailities of the class A amps?
4. If I do decide to buy a class A amp how far back in years should I venture? Right now I am considering the Mark Levinson 27 or 27.5 or Pass Labs X150/250 and X150.5 and X250.5 amplifiers. It's been suggested that the Mark Levinson is more musical????? I just want to get the best amplifier to run my audio system.

I will be driving Magnapan 1.6 speakers which does require a fair amount of amps/power to drive them. Also I mostly listen to classical music, large/small scale choral works, contemporary and gospel music and all modern jazz. I love the human voice. I also love a huge sound stage with lots of depth perspective.

Any assistance and suggestions you can provide will be very welcomed. Thank you so much for taking of your time to respond to this plea for help.
rbwinterlink
atmasphere's avatar
atmasphere
7,068 posts
 
Elevick, a class A amplifier, by definition, is class A at full output. If not, it is called class AB. There is no exception to this definition- the amplifier is class A if the output device does not go into cutoff at full power.

It is true that class A amplifiers last just as long as any other type of amp. They do run hotter- trading efficiency for improved sound quality. Class A operation is the most desirable mode of operation if the best sound quality is your goal. All other classes of operation trade off greater power output (and less heat) for less sound quality. Unfortunately it is not so simple to say that all class A amps sound better than all other amps; that would only be true if that class A amplifier had all the other most desirable design attributes and was properly executed. What is the best of the other design attributes is controversial, but the class of operation is not.
viridian's avatar
viridian
4,184 posts
 
The first thing that cuts the life of an electronic circit is running the individual compents beyond their rated range, and the second is heat. Then again, a class A amp with adequite heat sinks and good ventilation can run cooler than a class A/AB amp with less adequite heat sinking.

Interestingly, none of the amps that you mention are class A amps, all are class A/AB, so more research is in order on your part.

In the end, you are buying sound quality, not circuit topology, so this should be your primary criteria.
guidocorona
4,114 posts
 
Rbwinterlink, in general it is best to turn off your system if you leave home for a few days regardless of the class of operation of your amp. . . besides power consumption concerns for all class A amps and many class A/B amps, there is the issue of inclement weather which can cause power outages, spikes, and worse.

Pure class A amps are -- as far as I know -- always furnaces. . . . as they draw current at the same peak value regardless of what they are doing. . . whatever is not used for making music goes up in heat.

Things become more murky with class A/B devices. Some are veritable furnaces like the Pass X.5 series and my old Rowland 7M monoblocks. . . others run as cool as cucumbers like the Theta Citadel monos -- one of the sweetest amps I have ever heard.

Then there are switching amps -- mostly class D -- that most often run very cool to the touch and have operating efficiency ranging from 85% to 98% depending on manufacturers and models. In most cases these amps have output properties (high damping factor of 500 to 1000) that make them particularly suitable for driving low impedance speakers like Magnepan 3.6. I listen almost exclusively to classical music and my amp is a class D Rowland 312, which runs cool even in the sweltering summers of Austin. . . I couldn't be happier about its sweetness and its power to deliver staging, imaging, detail, and nuance.

Besides power draw from all class A and some class A/B amps, I would not be terribly concerned about the inherent musicality of any class of operation. You will find musically satisfying amplifiers in class A, A/B, and D alike, and at least as many that will put your teeth on edge -- no matter what their class may be.

Guido
warrenh's avatar
warrenh
2,286 posts
 
regarding Pass Labs amps: given that I have 101dB speakers, am I correct in my thinking that their very pricey (but extraordinary from what I've read) Xa series would sound the same as their other models in the class A mode? At 101db, I can go to serious dbl levels in the 15 watt range, but would love to have that extra wpc, for those rarely needed ear bleed, moving picture frame levels, given that my speakers can handle 300 watts. Anyone?

warren
atmasphere's avatar
atmasphere
7,068 posts
 
Hi Warren, The Zu Definition is available in a 30-ohm version. All the reports I have is that this version of the speaker is really something to hear, and it can be easily driven by smaller tube amplifiers, which will sound a lot better driving 30 ohms than they will 3.3 ohms.

If you are set on going solid state, I would consider one of the First Watt amplifiers, rather than something that makes 300 watts. The First Watt amps need more efficient speakers, but they also sound better- and will be very happy with a 30 ohm load, should you decide to go in that direction.
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