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So Class A - do it if you haven’t!

Arkless Electronics said:
180W is too low for 45WPC in class A. 235W sounds more like it. In fact everything in the Accuphase would have to be >100% efficient!!:rolleyes:
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Yes agreed obvs. The A1000 (50w) demands 215w continuously..

The easy way to tell if your amp is class A - If it gets really hot when it’s playing nothing.. then it’s class A.

If it gets hot when it’s only playing music then it’s not Class A!

The output devices in a class A amp are always on 100%, so heat is produced in spades when it’s sitting idle. In fact I read that when playing loud, a class A amp actually gets cooler, (as it’s using some of the always on 100% output to output music) so the heat output drops.. How cool is that.

I believe that a proper Class A amp has been built to run at the temperatures they inherently get to, with engineers building the output devices at the top and with sufficent heat sinking, so comments about reducing life of components I don’t think should be worried about too much… it’s a bit like saying that I worry about my car engine because it gets hot - it’s been built to cope..!
 
Rug Doc said:
Yes agreed obvs. The A1000 (50w) demands 215w continuously..

The easy way to tell if your amp is class A - If it gets really hot when it’s playing nothing.. then it’s class A.

If it gets hot when it’s only playing music then it’s not Class A!

The output devices in a class A amp are always on 100%, so heat is produced in spades when it’s sitting idle. In fact I read that when playing loud, a class A amp actually gets cooler, (as it’s using some of the always on 100% output to output music) so the heat output drops.. How cool is that.

I believe that a proper Class A amp has been built to run at the temperatures they inherently get to, with engineers building the output devices at the top and with sufficent heat sinking, so comments about reducing life of components I don’t think should be worried about too much… it’s a bit like saying that I worry about my car engine because it gets hot - it’s been built to cope..!
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Transistors have thermal ratings and even a medium power class A amplifier quickly becomes impractical in domestic settings.

I consider the 60W Emotiva monos as mostly impractical and would not have bought them unless they had the quiescent current switch.

Anything larger than that will require active cooling, which is really problematic.
 
Rug Doc said:
Yes agreed obvs. The A1000 (50w) demands 215w continuously..

The easy way to tell if your amp is class A - If it gets really hot when it’s playing nothing.. then it’s class A.

If it gets hot when it’s only playing music then it’s not Class A!

The output devices in a class A amp are always on 100%, so heat is produced in spades when it’s sitting idle. In fact I read that when playing loud, a class A amp actually gets cooler, (as it’s using some of the always on 100% output to output music) so the heat output drops.. How cool is that.

I believe that a proper Class A amp has been built to run at the temperatures they inherently get to, with engineers building the output devices at the top and with sufficent heat sinking, so comments about reducing life of components I don’t think should be worried about too much… it’s a bit like saying that I worry about my car engine because it gets hot - it’s been built to cope..!
Click to expand...

Ah but the cheaty companies will make say a 50WPC amp and call it class A but not tell you that it's only class A up to 20W... then save money by using a heatsink only big enough for 20W class A plus the other 30W in A/B. That heatsink will still need to be big, just not as ginormous as ones for a real 50WPC, and as they are smaller they will get just as hot as the ones on the 50WPC class A job. The (verified) actual power draw is a reasonable ballpark answer after allowing for PSU not being 100% efficient and power for pre amp section, protection circuitry etc etc. On an accurate bench Wattmeter you will see the power draw increase when it moves into class A/B... basically... it's now having to take more power in from the mains to go to the speaker rather than taking it from the power that was making the heatsinks hot... that's as in very basicallyo_O:)
 
Arkless Electronics said:
180W is too low for 45WPC in class A. 235W sounds more like it. In fact everything in the Accuphase would have to be >100% efficient!!:rolleyes:
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I'm old school. If the amplifier is more than 30% efficient, it can't be class A for the rated power. My Pioneer M-22 turns at least 75% of its energy consumption as heat. It is proper class A, even if it is not single-ended. ;)
 
Arkless Electronics said:
Ah but the cheaty companies will make say a 50WPC amp and call it class A but not tell you that it's only class A up to 20W... then save money by using a heatsink only big enough for 20W class A plus the other 30W in A/B. That heatsink will still need to be big, just not as ginormous as ones for a real 50WPC, and as they are smaller they will get just as hot as the ones on the 50WPC class A job. The (verified) actual power draw is a reasonable ballpark answer after allowing for PSU not being 100% efficient and power for pre amp section, protection circuitry etc etc. On an accurate bench Wattmeter you will see the power draw increase when it moves into class A/B... basically... it's now having to take more power in from the mains to go to the speaker rather than taking it from the power that was making the heatsinks hot... that's as in very basicallyo_O:)
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Sounds like you described the Musical Fidelity A-100 I once had. I think it was good for about 10W class A.
 
James said:
I'm old school. If the amplifier is more than 30% efficient, it can't be class A for the rated power. My Pioneer M-22 turns at least 75% of its energy consumption as heat. It is proper class A, even if it is not single-ended. ;)
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50% for push pull class A as theoretical max efficiency at full power if all components etc were perfect. A bit less in practice obvs.
Much lower for many (not all) SE types and can be 12.5%!

Yep about 10-15WPC class A for A100. A1 is class A all the way. As the A100 can give 50WPC it draws more at idle than the A1 does to give all of its 20WPC in class A, hence it has cooling fans fitted.
 
I run my vitus in class b for daytime listening, class A for when paying attention, I can hear a vast improvement when it’s hot in class A. Having said that I had Avalon ideas for a few years and they didn’t really get much better in class A. They actually sound fab with the Vitus 101, it’s high A\B output worked a treat. So it’s as they always say suck it and see.
 
Arkless Electronics said:
Ah but the cheaty companies will make say a 50WPC amp and call it class A but not tell you that it's only class A up to 20W... then save money by using a heatsink only big enough for 20W class A plus the other 30W in A/B. That heatsink will still need to be big, just not as ginormous as ones for a real 50WPC, and as they are smaller they will get just as hot as the ones on the 50WPC class A job. The (verified) actual power draw is a reasonable ballpark answer after allowing for PSU not being 100% efficient and power for pre amp section, protection circuitry etc etc. On an accurate bench Wattmeter you will see the power draw increase when it moves into class A/B... basically... it's now having to take more power in from the mains to go to the speaker rather than taking it from the power that was making the heatsinks hot... that's as in very basicallyo_O:)
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Another thing that happens is to make a very warm 75-80W AB amp that's class A up to 50W, and market it as a 50W Class A amp. People will say "oh it sounds so powerful for 50W!" And it doubles its power into four ohms...
 
Yank said:
Another thing that happens is to make a very warm 75-80W AB amp that's class A up to 50W, and market it as a 50W Class A amp. People will say "oh it sounds so powerful for 50W!" And it doubles its power into four ohms...
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Yes! I've explained that con of exactly doubling the power into 4R like that a few times on pfm:)
 
Arkless Electronics said:
50% for push pull class A as theoretical max efficiency at full power if all components etc were perfect. A bit less in practice obvs.
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Aha! So the Accuphase cannot really be class A up to its rated output into 8R cos that will make it perfectly 50% efficient. I will have to rethink my Accuphase aspirations :D

Arkless Electronics said:
Yep about 10-15WPC class A for A100. A1 is class A all the way. As the A100 can give 50WPC it draws more at idle than the A1 does to give all of its 20WPC in class A, hence it has cooling fans fitted.
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All the cooling fans did was suck in dust that coated (and insulted) everything inside, thus guaranteeing it would self-combust within a very short time. Mine lasted two years.
 
Ok I haven't read the whole thread but I'll weigh in with my thoughts

My first class A was a cheap Chinese valve amp with few watts. It sounded sublime. I loved it, great value, but not loud enough maybe. I tried different valves in it based on net posts and blew a main transformer. RIP.

Second, JLH 1969 based amp but with 4 transistor amps per channel, about 15w theoretically (but probably not really). Really sparkly high end. Very good elsewhere, best amp so far maybe.

In the last week, PASS A30 based chinese power amp. Not really as good in the top end perhaps as the previous amp, but amazing musicality and bite. Great for those who like their speakers driven punchily. As good as the last amp, maybe better, they both have their strengths, but this amp at least goes loud enough (much louder than last).

My endgame was a Sudgen unit but I am happy for now. I am really amazed at how my Triangle BR08 speakers are responding to amp change.
 
The JLH has just audible "nice" distortion levels, the little Chinese valve probably had even more.
"Sparkly" is added 2nd and 3rd order.
 
James said:
Aha! So the Accuphase cannot really be class A up to its rated output into 8R cos that will make it perfectly 50% efficient. I will have to rethink my Accuphase aspirations :D


All the cooling fans did was suck in dust that coated (and insulted) everything inside, thus guaranteeing it would self-combust within a very short time. Mine lasted two years.
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The Accuphase brochure describes the amp as using an ‘instrumentation amplifier topology’ and I’m curious as to what this means. Is it just marketing BS, or might it have a bearing on matters?

There’s also some form of source signal detection, because it powers down after a period of mo music signal. Is it possible this could also be used to reduce the idle current draw a bit?
 
Sue Pertwee-Tyr said:
The Accuphase brochure describes the amp as using an ‘instrumentation amplifier topology’ and I’m curious as to what this means. Is it just marketing BS, or might it have a bearing on matters?

There’s also some form of source signal detection, because it powers down after a period of mo music signal. Is it possible this could also be used to reduce the idle current draw a bit?
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An instrumentation amp is a 3 op amp circuit for a balanced input amplifier with easy gain adjustment. It could be used in the pre amp section but it's about as generic a circuit as is possible.
 
It probably needs saying that class A does not have any specific sound and is not a guarantee of audio nirvana. There can be better and worse class A amps just as with any other type and a good example of another type could well beat a less than ideally implemented class A amp.
 
Arkless Electronics said:
It probably needs saying that class A does not have any specific sound and is not a guarantee of audio nirvana. There can be better and worse class A amps just as with any other type and a good example of another type could well beat a less than ideally implemented class A amp.
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That is very true. I've three, soon to be four, A class amps (all DIY I should add, two clones and two NP) and they don't sound the same - I certainly prefer one over another.

And as a long time owner of Avondale Voyagers, I prefer my KSA50 clone. :)
 
Arkless Electronics said:
Hmmm it has pretty low distortion when put together right... low enough to be inaudible. A little below 0.1%
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Around that value if the parts got the right hfe. I think that JLH must have had 8 to 15 Ohm speakers in mind when he designed it, it is not optimised for so called 6 Ohm loads. This makes sense for the era.
It simulates as clipping very softly, around 0.5 % THD before running out of steam, so maybe "just" audible, not a fuzz box.
Elegant in its simplicity.
 
davidsrsb said:
Around that value if the parts got the right hfe. I think that JLH must have had 8 to 15 Ohm speakers in mind when he designed it, it is not optimised for so called 6 Ohm loads. This makes sense for the era.
It simulates as clipping very softly, around 0.5 % THD before running out of steam, so maybe "just" audible, not a fuzz box.
Elegant in its simplicity.
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It's certainly for 8R loads in standard form but JLH gave values for optimisation for 3 and 15R also . JLH says 0.06% at 9W for optimum hfe.

Yes it is indeed elegant in its simplicity:)

The later 1996 update would be the one to go for and there are various further upgrades from other people in articles on the class A web site.... even a 50W version intended for ESL's IIRC.
 
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