So, are Class A power amplifiers actually any good?

[dlaloum]

Your reasoning ignored the difference between the crest factors of music and a single tone sine wave.

For music, per the AES reference linked below, its crest factor typically ranges from 4 to 10 (12 to 20 dB). Single tone sine waves, the test signal to establish amplifier power ratings, have a crest factor of 1.41 (3 dB). What it means is that, if the amplifier starts to clip at 13W into 8 ohm, with music that has a 12 dB crest factor, the clipping point of the amplifier will be 9 dB less, which is 1.6 W.

https://www.aes.org/par/c/#cps

View attachment 276757

Hmmm part of the issue I was pointing to, is that the graph shown is that of the continuous power output capability of the amplifier...

And yes I was talking about crest or peak capabilities, based on 20db headroom.

But the data from that test, and from Sugden themselves - provides us with no information as to the peak/crest capabilities of the amp.

So we know that for 4ohm it can drive continuous 13W rms.... but what can it do it "music power" terms (often used by manufacturers to obfuscate lack of continuous power capacity in their amps, but absolutely relevant in understanding an amps ability to handle the "crests" / Peaks for brief periods of time.

We can guarantee that it can provide for peaks within its continuous parameters as quoted... what we don't know, is how much headroom it has above and beyond that... and for Class A or AB amps that headroom is usually substantial.

 

[Blumlein 88]

I understand pointing out the Sugden amp might do a little better than seems at first glance. Yet it is very expensive and not a good performer. My 40 year old stereo receiver has lower distortion (in it's case also some 2nd and 3rd mainly) with more power, more current, more load tolerant and was much less expensive back in 1983. Plus it still works just fine. I'm amazed the caps seem alright in it still.

 

[dlaloum]

I understand pointing out the Sugden amp might do a little better than seems at first glance. Yet it is very expensive and not a good performer. My 40 year old stereo receiver has lower distortion (in it's case also some 2nd and 3rd mainly) with more power, more current, more load tolerant and was much less expensive back in 1983. Plus it still works just fine. I'm amazed the caps seem alright in it still.

Sugden have never been cheap! (UK's competitor with Krell?)

And of course, much of the power supply capacity, gets wasted as heat.... the joys of Class A - so your Receiver, running in either AB, or one of the various Pseudo Class A modes, with some feedback in the system, will almost invariably measure better.

 

[Piere]

If you like or like not class-A Sugdens is a matter of taste. It will be an endless debate. Technical arguments are moot imho.

 

[roog]

My impression of Sugden Audio was that they adopted the class A topology back in the 1960's as a means of getting around the issues of crossover distortion presented by class B. So rather than solving the issues of class B, they avoided them, and put up with the consequences of going with class A. I guess it was a way of gaining traction in the market using these new fangled power transistors when thermionic valves/tubes were 'king' and where no doubt the producers of which where keen to put down the flaky new transistor, and 'pretender'.

Since then I believe they have latched on to this on to this stance as it appeals to macho Audiophiles who believe the only way to good sound is to suffer the; cost, weight, heat and low power generated by such designs. Their masterclass amps certainly continue in this vain.

 

[HarmonicTHD]

If you like or like not class-A Sugdens is a matter of taste. It will be an endless debate. Technical arguments are moot imho.

Yes personal preference is futile to argue with, however personal preference (taste) only applies to the individual and therefore is irrelevant for everyone else. So why even recommend something based on your taste?

That’s why we have technical performance measurements, because they assess the equipment independent of personal taste. And in that league the Sudgen is wayyy below state of the art. Whether you make that part of your purchasing decision, is up to everyone individually - but at least you have a choice to make an informed decision (and not rely on subjective anecdotes based on „tastes“).

 

[Piere]

If you opt for a Sugden class-A nowadays, you don't do that for rational technical reasons... Apart from house warming maybe?

 

[notsodeadlizard]

The concept of "good" is conditional, the concept of "corresponds to the declared parameters" is unconditional.
Otherwise, it's enough that people love class A amplifiers and are willing to pay money for them.
This is called freedom of choice.

 

[RayDunzl]

Here's a link to some measurements on my Krell FPB 350 mcx monoblock.

Krell FPB 350 mcx

A quickee look and see... Bought 9 years ago used, no rebuild, no repairs, no faults. Serial number indicates 2005 build date. Left monoblock, approximately 5W/4Ohm tone, loaded by the speakers: Not great... Left Channel. 695 more rated watts available, though. Let's see: THD 0.012%...

www.audiosciencereview.com

Measurements taken at the amplifier output terminals at various idle stages and approximately 5W output three years ago.

Noisy environment - rats nest cabling, preamp sits on top of isolation transformer, flanked by monoblocks.

 

[Matias]

AFAIK the best measuring class A amplifier I have found until this day is the Accuphase A-250 with SINAD 94 at our standard 5W at 1 kHz into 4 ohms, and max power 350W also at the standard 1 kHz 1% THD+N into 4 ohms. Beautiful chassis, but for 59k USD it is mandatory.

 

[voodooless]

AFAIK the best measuring class A amplifier I have found until this day is the Accuphase A-250 with SINAD 94 at our standard 5W at 1 kHz into 4 ohms, and max power 350W also at the standard 1 kHz 1% THD+N into 4 ohms. Beautiful chassis, but for 59k USD it is mandatory.

This thing did much better: https://web.archive.org/web/2017081...842.5/extrema-reference-class-a-diy-amplifier

Published in Dutch version of Elektor in about 2007 as a DIY design for about € 500 per channel (back then). Obviously, it did not do 350W, but will satisfy any SINAD fetish you might have.

 

[Matias]

Yes, this and pma's amp look great as far as SINAD goes... until we check the max power they provide.

 

[voodooless]

Yes, this and pma's amp look great as far as SINAD goes... until we check the max power they provide.

At least those are not $ 60K

 

[fpitas]

Since we're posting THD graphs, the First Watt J2:

At 20mW where I use it, not bad. Not much power, so I'm not sure how people use it with cone speakers, but that's their problem.

 

[voodooless]

Since we're posting THD graphs, the First Watt J2:

View attachment 276844

At 20mW where I use it, not bad. Not much power, so I'm not sure how people use it with cone speakers, but that's their problem.

This is only THD, right? excluding N?

 

[fpitas]

This is only THD, right? excluding N?

He claims it's mainly 2nd harmonic.

https://www.firstwatt.com/pdf/prod_j2_man.pdf

At any event, I doubt I hear the 0.008% THD it's making.

 

[voodooless]

He claims it's mainly 2nd harmonic.

https://www.firstwatt.com/pdf/prod_j2_man.pdf

At any event, I doubt I hear the 0.008% THD it's making.

Well, noise is claimed to be 100uV, at 20mW which is about 66 dB down, so way more dominant than the 0.008 THD figure. That's why I asked if the graph is only THD, which I think it is.

 

[fpitas]

Well, noise is claimed to be 100uV, at 20mW which is about 66 dB down, so way more dominant than the 0.008 THD figure. That's why I asked if the graph is only THD, which I think it is.

Good point. From a practical standpoint, with my ear against the horn mouth I can barely hear the hiss.

 

[Mike1711]

Let’s see here:
View attachment 276645
Makes barely 13W@R8, 22W@R4. Best case SINAD is about 77. By any standard, that is poor performance. 3k US for 13W is reasonable? I guess this things is better at projecting a reality distorted field than amplification…

So let me know when we listen to measurements. Listening a Steinway vs a Yamaha piano. Very different sound. However is the difference worth the additional price. Well if you have the legs why not…?

 

[voodooless]

So let me know when we listen to measurements. Listening a Steinway vs a Yamaha piano. Very different sound.

An amplifier is not a musical instrument. It should not sound like anything.