How Bad is Owning Class A?

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BLASTO

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Hi Guys,

I have query on owning/maintenance of class A amplifier and any special care/precaution to be taken?

I have stayed out of class A/Tube amp arena this long but looks like I have to venture into it sooner or later.

Can a class A be treated as carelessly as a class AB?

How to live with the heat?

Can they survive Indian summers without A/C?

Can they break down due to over heat?

Owners who own class A's please let me know what extra maintenance you do from your class AB days and whether it is a wise move considering all the trouble.

Thanks,
 
If the Amp is designed well, Its exactly the same as you would do with any other amplifier in terms of maintenance

The only difference is that you will need to shut it off when not using it as in a pure Class A , the draw of power is constant and what it does not use by driving the speakers, it dissipates as Heat.

Also usually Class A has an efficiency of 10-20% hence a 25W amp may pull in 250W all the time.
 
Have recently visited an FM's home in Delhi who is operating a Krell 400xi integrated SS amp. This amp spec states its circuit to be of Class A type till the outputs.

As per the FM, he admitted the amp to get pretty hot during long operations (would find it difficult to touch it on the top ... so hot) in summers, even with the AC on. In winters, it gets tolerably hot. The amp body is made of heavy gauge aluminium, which is superior to painted GI (as with most other amps) in dissipating heat.

To counter this heat issue, this gentleman has installed a 4" dia computer cooling fan inside the amp which blows out the accumulated heat within, thru the top grills. The fan comes on when the amp is put on active mode from stand-by. This heat blow-out assists in very good results with the amp running in a mild-hot zone even during summers.

Excess heat generated if not blown away definitely does 'bad' damage to certain components, like resistors. As per the FM, he had to replace close to 10 nos. of 1 to 5 ohm resistors (before going in for the fan solution), since the resistance values had all increased and started creating sound distortions.

Hope that helps.
 
Krell K400 class A ? I dont think it is a pure Class A but could be some Hybrid design with the major portion in AB or it might be biased upto a point at Class A.
its impossible to fit a 150W Class A design into the size of this krell...they fall into the pass Labs category. Even a 50 W class A would be easily 30+ KG in weight

I had a 25WClass A (Sugden) for almost 5 years and never gave Any trouble..it is still with someone and as far as i know still going great guns. a badly designed Class A is a different matter altogether.

I would think there is some other problem with the Krell...it is not supposed to run that hot,..and definitely not fail as it is doing

The Pass Labs/Old Krell KSA series /Accuphase A series etc amps are all class A and even if you buy a 10 year old one they will still run for quite a few years

here s a Krell Class A amp..even this is not a pure Class A as it is biased to usually 80% at Class A and the rest being Class B
999krellksa100s.jpg
 
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Yes, the 400xi is not Pure class A, but as per its specs (check google) a major part of the circuit is of Class A.
 
BLASTO said:
Hi Guys,

I have query on owning/maintenance of class A amplifier and any special care/precaution to be taken?

I have stayed out of class A/Tube amp arena this long but looks like I have to venture into it sooner or later.

Can a class A be treated as carelessly as a class AB?

How to live with the heat?

Can they survive Indian summers without A/C?

Can they break down due to over heat?

Owners who own class A's please let me know what extra maintenance you do from your class AB days and whether it is a wise move considering all the trouble.

Thanks,
Click to expand...

Class A amplifiers always have had a good reputation among audiophiles. Talking about audio power amplifiers, the picture is quite different. Here class B and A/B amplifiers play a dominant role, while class A is more seldom. Disadvantage of using class-A amplifiers is the fact that their efficiency ratings are so low, approx 25% .

Why?? A majority of the power that is drawn from the supply by a class-A amplifier is used up by the amplifier itself. Class A draws a lot of current at idle.
The reason why there are not many high NFB class A amps is simply that low THD-numbers can also be achieved without Class A output stages. Why running the output gleamingly hot if it does not bring any benefit?

Consider the example with the 100 W amplifier, where the output transistors alone dissipate more than 200 W. This requires large heat sinks. Using a conventional heat sink as an example, having an effective thermal resistance of 0.25 W/K, the temperature will rise with more than 50 degrees above ambient temperature. Adding the fact, heat sinks can not dissipate that heat efficiently in real life living room conditions , we already have two reasons to avoid class A drive.

Regards
Krishna
 
I had an Opportunity to listen to the Sugden A 21a Pure Class A amplifier. Its only 20 watts, but the sound is so clean and it matched beautifully with my Zingali speaker. The Sugden even put my **** Tube amplifier to shame. But the guy who gave me the A 21a for listening did not have any idea of selling it to me :mad:
Class A is the way to go if you want Clean Power and a Melow Midrange. But these amplifiers are always expensive:sad:

Cheers
 
Sugden is one of those very great names of hifi. Perhaps the design and engineering had as much to do with the resulting sound?

My Bravo Ocean tube headphone amp is class A. Even though it so tiny, it is hot enough to cook a meal on!

Next month I will buy an iFi iCan headphone amp. It seems this is class A too. I don't remember it being hot when I first saw it in the shop six months ago. I had never thought about the technology, yet is coming my way!

Of course, these are very small things, nothing like a big power amp --- although the Bravo just might produce almost as much heat :lol:.
 
ghatgepatil said:
Yes, the 400xi is not Pure class A, but as per its specs (check google) a major part of the circuit is of Class A.
Click to expand...

My understanding is that the place where Class A matters is the output stage as thats where switchover distortion is the most prevalent .. I think !.this is most probably class AB :).
I would guess the marketing spin doctors have a hand here as almost all Pre stages in an Int amp are Class A...maybe there is some changes to make this more possible..
I hope the person you listened this to has talked to Krell on this..Krells are Not supposed to fail as has been described- definitely an issue

Anyway this is a wrong Amp to compare on Class A as the real krells were those of the old. the 300x itself was considered a step down and the 400 a deviation from what krell stood for. Those KSA series are legendary.
 
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soundofmusic said:
I had an Opportunity to listen to the Sugden A 21a Pure Class A amplifier.

Cheers
Click to expand...

thats the one i sold :sad: i spoke to this gentleman in Coimbatore..had often thought of keeping it but then that would be a waste of space and a great product lying unused
 
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How bad? Very bad. You will not feel like listening to other amps, anymore:)

But, as others have pointed out, they produce lots of heat. My amp is 80 Watts of claimed Class A. I said claimed, because I don't know if it is Class A all the way. It does get very, very hot. The rack MUST have enough room on top of the amp. I leave about 9 inches from the top of the amp to the bottom of the layer above.

My older power amp was a tubed hybrid producing 60 Watts. It used to get much hotter than the current silicon 80 Watts. And it used to come on song only after operating for about an hour. The usual listening routine was to switch on the amp, play something in the background or just leave it to heat up for an hour and then get down to listening. The heat up time was one BIG reason I moved to solid state.
 
Class A is actually the simplest design but not used because of its high inefficiency its only 10% efficient as it takes the full power rating irrespective of the load (and hence the smooth sound). the challenge here is in designing and quality of components. it also is usually low power and as the impedance reduces usually its power also falls
eg the Sugden A21a is 25 w x 8 ohms, 16 watts into 4 and falls rapidly with 2. hence needs fairly efficient speakers which give an easy load. but since the limited dynamic power is instantaneous, it feels it is far more powerful


Class AB splits the signal and draws the current based on its need and hence its is more than 60% efficient although it needs to be really well designed to get an organic sound. Most Class ABs behave like a class A (Biased) upto a certain level and then becomes a CLass AB thus conserving power

there are Class ABs which sound Better than a Class A and vice versa and if your speakers need more power then you are better of with a Class AB. for the price they give more bang for the Buck

so , its is not that Class As always sound good
 
I wonder how this thread narrowed down to the sugden since I never mentioned.. :)

I am actually narrowing down to a sugden A21se. Class A is one of the biggest hurdles on the way
 
BLASTO said:
I wonder how this thread narrowed down to the sugden since I never mentioned.. :)

I am actually narrowing down to a sugden A21se. Class A is one of the biggest hurdles on the way
Click to expand...

with a sugden the last thing you will need to worry is maintenance !. one of the best amps in terms of purity of sound as well as design as long as the speakers are not a tough load.
its the best example of a Tube sound from an SS amp (of course at that price range)
 
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