Class A

[Guest]

Pro's and Cons please

PS. Spare me the narcotics jokes

 

[Alex A]

Well it's simple.

Cons: Very hot, either very big or smallish and (very) low powered, very power hungry, potentially high maintenance, sharp heat sinks, etc. etc.

Pros: IF done right, IMO, you can get the kind of combinations you tend not to find with other classes of amplification: smooth AND transparent. Powerful, rhythmic, controlled bass AND a lush, beguiling mid. The ability to rock your house or to keep your attention on quiet listening sessions.

What you get and don't get will of course vary with the particular design. You could say that it's a very internally varied field. But you don't find many bad Class A amps.

 

[ob1]

Sound like the pro out do the con, although when I listen to Marantz 7200 class A/B sound a lot better than class A on the same machine.

 

[Alex A]

It makes hardly any difference on the 7200 IMO. But compare the Marantz A/B mode to a Sugden A21a integrated into the right speakers and I'm sure you're impression will be very different.

 

[Ant]

Much more simple than all that, in push pull class A you effectively eliminate crossover distortion when switching between the output devices.

 

[meninblack]

You really do need sensitive speakers though!

 

[nixon_fiend]

not with a krell

 

[Guest]

Well i've borrowed from Ant his MF A100. Which operates in class A for up to 93% of its quoted 50 watts a channel. It goes loud and i mean plenty loud for a normal living room. My speaks are 89 in the sensitivity stakes. So it just got me wondering. Oh and yes it gets bloody hot..

 

[El Seano]

Speaker considerations are a important point but it is surprising at some of the combinations that work well. I heard an a21a (original version) driving wilson benesch Arcs very effectively (and pretty loud!) whilst on paper you wouldn't think that they would make a good combination.

Ain't class A brilliant!?! i love it anyway

 

[meninblack]

Duvet wrote:

Well i've borrowed from Ant his MF A100. Which operates in class A for up to 93% of its quoted 50 watts a channel. It goes loud and i mean plenty loud for a normal living room. My speaks are 89 in the sensitivity stakes. So it just got me wondering. Oh and yes it gets bloody hot..

50W! :shock:But that's only a clock-radio, according to ... err ... um ... MF

.

 

[Guest]

meninblack wrote:

Duvet wrote:

Well i've borrowed from Ant his MF A100. Which operates in class A for up to 93% of its quoted 50 watts a channel. It goes loud and i mean plenty loud for a normal living room. My speaks are 89 in the sensitivity stakes. So it just got me wondering. Oh and yes it gets bloody hot..

50W! :shock:But that's only a clock-radio, according to ... err ... um ... MF

.

Yes i know. It constitutes the mother of all U-turns in company philosophy :lmao:

 

[Jezzer]

I've owned a couple of SS amps with a strong bias towards class A and have always liked the warm, detailed and airy sound. Tempted to look at the Sugden A21 mk2 as my next amp... (but for the (new) price of one of those I could get another (used) Krell KAV400xi...)

 

[i_should_coco]

As others have said, it's easier to build a good class-A amp than one that uses class-AB because it eliminates crossover distortion.

N.B. single-ended amps *must* be class-A.

The only real downside is poor efficiency which is maximum 25%, i.e. a maximum of 25% of the input power is available for output.

An interesting side effect is that class-A amps tend to run cooler when actually in use.

Cheers,

Pete

 

[murray johnson]

Duvet wrote:

Well i've borrowed from Ant his MF A100. Which operates in class A for up to 93% of its quoted 50 watts a channel.

In its dreams, perhaps

These are the early Mark Levinson ML2 mono amplifiers which really were 25 W per channel in Class A. Look at the amount of heatsinking required to get rid of the heat that needed to be dissipated. Compare that with almost any modern 'so called' Class A SS amplifier.

Biscuit's 30W Pioneer is a massive lump with fans too. Far bigger & heavier than the MF.

No, MF were masters of BS back then too.

It is different with valve amps. They can also dissipate heat by radiation as well as conduction.

 

[i_should_coco]

murray johnson wrote:

Duvet wrote:

Well i've borrowed from Ant his MF A100. Which operates in class A for up to 93% of its quoted 50 watts a channel.

In its dreams, perhaps

Maybe it's 93% of the time. i.e. playing music where it never gets above a handful of watts....

45W class-A would require a minimum quiescent dissipation of 360W! more like 400 I would expect. Out of interest, what does the back panel say?

 

[Alex A]

Murray: you don't believe the A21a spec? The only reason that still isn't a 12W design is that they managed to improve the efficiency of the circuit and transistors closer to the ideal for class A than they could with the original components available in the '60s.

I'm not supporting the MF claim about the A100, just saying that it's certainly possible today to get a true 25 transistor class A watts out of something a lot smaller than that early ML amplifier. You also have to consider that those ML will last almost forever precisely because they were built so massively (and cost a fortune), whereas things like the MF are traditionally much less reliable, indicating that they do indeed run (too) hot in an attempt to be as powerful in Class A as possible.

 

[Biscuit]

i_should_coco wrote:

murray johnson wrote:

Duvet wrote:

Well i've borrowed from Ant his MF A100. Which operates in class A for up to 93% of its quoted 50 watts a channel.

In its dreams, perhaps

Maybe it's 93% of the time. i.e. playing music where it never gets above a handful of watts....

45W class-A would require a minimum quiescent dissipation of 360W! more like 400 I would expect. Out of interest, what does the back panel say?

35Wrequires over400W in my trannie amp

and its bloody big

no fans required though Murray

 

[enjoy_the_music]

Yeah there are lots of facets to this whole Class A ranking. There is a lot of BS flying around from manufacturers.

Just saying Class A doesnt mean instantly good sound.

 

[earl of sodbury]

I suspect the MF is heavily class-A biased but still switching, most MF amps more-or-less are, as are the various Cairns...

...and I know which I IMMENSELY prefer

Danny, see if Ant will part with the Meas for a few days :green: