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Have amplifiers finished evolving?

I thought they sounded distorted with a nasty top end, I wouldn't keep them if you gave them to me. I went back twice to give them a chance with different music (because of all I've heard about them, and the idea of them, and the price-point) but I got the same impression. I should point out:
- It was at a show
- It was in a big room, playing loud, and they're small things
- I think they were being EQd a lot

So it may be they were being badly over-driven, especially at certain frequencies. They seemed to be fronted by a Chord Hugo, when I thought the point was no front-end DAC was needed? And no speaker likes being over-driven. Which means shame on the demonstrators.

I make decisions based on experiences as much as the next person, so no. But I'd give them a chance under different circumstances - maybe with no EQ and in a smaller space at reasonable volume they would be amazingly better. That's a reasonable guess, since I liked the Kef Blade 2 (passive with MF amps) a lot.
 
darrenyeats said:
I thought they sounded distorted with a nasty top end, I wouldn't keep them if you gave them to me. I went back twice to give them a chance with different music (because of all I've heard about them, and the idea of them, and the price-point) but I got the same impression. I should point out:
- It was at a show
- It was in a big room, playing loud, and they're small things
- I think they were being EQd a lot
Click to expand...

I didn’t get even the slightest hint of that, though I don’t listen loud (they went far louder cleanly than I’d ever want). I don’t think we hit more than about 80db average (I used my phone as a sound meter as I like to hear things at a similar level I listen at home).

The room was of average to slightly larger than average living room size (rather larger than I’d chose to use a mini-monitor myself), they were positioned well away from walls on lovely original cast metal AE1 stands from the 1980s and as I mentioned above sources were distinctly high-end (the Avid/Graham/DV turntable and Icon phono stage has to be £15k+ and the Roksan CD used as a transport wasn’t cheap). Initially they were setup with a very fancy digital B&W sub which I felt did the bass quite well (it almost convinced me and I hate subs!), but I felt the mid and top sounded flat, 2d and a bit thin. Removing the sub from the room and resetting the high-pass filter which was rolling the LS50s bass fixed this entirely and they now sounded really nice and open, clear and presented a proper wide and deep 3d soundstage without any hint of brigtness or tizz. They sounded dynamic, agile and fun.

As I say I liked them a lot and I really tend not to like speakers with metal dome tweeters, i.e. had the top been bad I’d really have been all over it and blaming the tweeters! I’d recommend them to folk looking for a neat all-in-one system for £2k or so (with the usual caveats of Chinese manufacturing and putting all ones eggs in one basket when it comes to serviceability).
 
I'll certainly give them another chance in hopefully better circumstances, it's one of those products I want to like.

I agree that room, positioning, set up and usage that's sympathetic to the design can make a huge difference with any speaker.
 
Jim Audiomisc said:
I've always been slightly wary of the terms Class A, B, etc, because the devil tends to be in details they can overlook. e.g. with the Armstrong 700 series power amp I chose to have the drivers connected to the output (via emitter resistors) in a way similar to the output devices. The result was that they acted a bit like a 'class A filler' for low voltages in the performance region were ther output devices were handing over. You can find similar but different details in other designs. So the division into 'classes' can be less clear than people assume.
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Hence class A/B which covers a multitude of sins.... I saw a schematic for the Creek CAS4040 the other day (which I hope was an inaccurate one!) as it shows this amp as having no bias... ie class B!
Check out Crown (Amcron) amps such as the DC300A for taking the idea you mention to it's conclusion.
 
Arkless Electronics said:
Hence class A/B which covers a multitude of sins.... I saw a schematic for the Creek CAS4040 the other day (which I hope was an inaccurate one!) as it shows this amp as having no bias... ie class B!
Click to expand...
Perhaps the circuit is as in here. It seems on first glance to operate like a poor cousin to Jim's Armstrong 732 arrangement (and like an incomplete Quad current dumper) with the driver stage coupled via C24 to a class B power stage output.

So Jim is right that we do have various class A+B arrangements that fall outside the conventional norms (and there's class A+D from Devialet as the most recent evolution).
 
Am I right in thinking Naim power amps are predominantly class B? And that class B somehow doesn’t need bias?

I need to do some proper reading at some point. I think I understand what class A is, know what a SET is, I even have an idea what a Quad current dumper is, but beyond that it all gets a bit foggy. I tried to find a good easy to understand explanation of the 303’s ‘triples’ a couple of days ago but didn’t really find much beyond it being a rather clever way of getting three fairly primitive transistors to behave as one very good one and in a way that makes the amp immune to bias fluctuations due to temperature somehow. As ever I’m at that point of having quite a lot of questions, but not the time (or ability to retain new stuff) to actually go and study electronics properly!
 
John Phillips said:
Perhaps the circuit is as in here. It seems on first glance to operate like a poor cousin to Jim's Armstrong 732 arrangement (and like an incomplete Quad current dumper) with the driver stage coupled via C24 to a class B power stage output.

So Jim is right that we do have various class A+B arrangements that fall outside the conventional norms (and there's class A+D from Devialet as the most recent evolution).
Click to expand...

No it's just class B and one of the worst amp designs I've ever seen going from the schematic...

All down to semantics on the amplifier classes. Class A/B or class A+B? There's lots of other permutations as well.. and check out class S from Sandman which was copied by Matsushita for "class AA". Further confusion arises from class G and class H having opposite meanings depending where in the world you are!! Doug Self wrote an article called something like "class distinctions in audio amplifiers" for those who want to look it up and read further.
 
Tony L said:
Am I right in thinking Naim power amps are predominantly class B? And that class B somehow doesn’t need bias?

I need to do some proper reading at some point. I think I understand what class A is, know what a SET is, I even have an idea what a Quad current dumper is, but beyond that it all gets a bit foggy. I tried to find a good easy to understand explanation of the 303’s ‘triples’ a couple of days ago but didn’t really find much beyond it being a rather clever way of getting three fairly primitive transistors to behave as one very good one and in a way that makes the amp immune to bias fluctuations due to temperature somehow. As ever I’m at that point of having quite a lot of questions, but not the time (or ability to retain new stuff) to actually go and study electronics properly!
Click to expand...

It's not so much a case of class B doesn't need bias as class B doesn't have bias... Class B is not hi fi and was used where efficiency was the prime concern such as modulation amplifiers for AM transmitters for communications purposes and for battery powered PA amps etc. They have huge crossover distortion where there is a gap in the transfer functions of the output devices... a chunk missing from the middle of the waveform if you like. Negative feedback is of limited use in dealing with it as there is no forward path through the amp in this crossover region, hence no amplification so nothing to feedback.... the best it can do is try and "speed it through" the crossover region.

When an amp is used in class A/B it can be "enriched A/B" ie it operates in class A for say the first 50mW to a few W or the bias can be reduced to what is known as optimum class A/B where a very specific bias gives the lowest distortion. This will generally be in the 5 - 10 mA region OR 35 - 80mA region depending on output stage type. Naim works in this way and with the lower current. I'll not bother explaining why their quasi complementary arrangement means it can never be fully optimised... it's near enough though...
 
cubastreet said:
Class D amps are more efficient. The obvious advantage is they use less power. Other benefits are that they don't need huge heatsinks (more compact, less cost) and you don't have all that heat to wear out your electrolytic caps.
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My integrated Class AB amp is 25 years old and so far the caps have not worn out , do not like Class D or G I have tried many amps including Devialet and can not find an amp that sounds better than my old one.
 
While we are discussing amplifiers what are fishies opinions on the optimum power for a class A amp? Think compromise here! 10W is more than enough if you have Tannoys or Klipsh etc but not much good for small inefficient mini monitors.... For 90dB/W speakers used at "normal domestically acceptable levels" in an average size UK room 10W would still be fine for many people but if you have a large room and like realistic levels obviously again no good....
Price, size, weight and heat start to get silly in class A if one insists on 50W or more.... So where's "the sweet spot"?

The range of volumes that people use/expect from their systems is huge IME.... I've been in rooms where I've commented "do you always play it THIS quiet?" as it's no louder than you would have the TV on.... no more than 1W max is ever being used here! I've been in other rooms where I've been pinned to the wall by the SPL with ears ringing after 10 mins:eek: They probably NEED 200WPC+ to guarantee no tweeter blowing clipping from the amp....
 
Years ago I found a pair of 10 watt JLH class A amps driving Quad 57s was perfectly adequate - I have since been told that`s not enough power....
 
Arkless Electronics said:
So where's "the sweet spot"?
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The sweet spot is wherever the crossover distortion disappears in a class AB amp.
I've never heard much benefit from class A. I 've built an Aleph 30 and a JLH 10W and there are better class AB amps out there.
The benefits of class A are well down in the hierachy compared to topology choice, compensation scheme and power supply IME.
 
Barrymagrec said:
Years ago I found a pair of 10 watt JLH class A amps driving Quad 57s was perfectly adequate - I have since been told that`s not enough power....
Click to expand...

Yep a mate used a Leak St20 (10WPC) with ESL57's and I was surprised at how loud it would go before obvious clipping or running out of steam...

My St20 or JLH 10W amps I've built in the past would both drive my KEF R105.3's (92dB/W) to "explaining it to the local constabulary level"!
 
S-Man said:
The sweet spot is wherever the crossover distortion disappears in a class AB amp.
I've never heard much benefit from class A. I 've built an Aleph 30 and a JLH 10W and there are better class AB amps out there.
The benefits of class A are well down in the hierachy compared to topology choice, compensation scheme and power supply IME.
Click to expand...

Class A is certainly no panacea for all ills.... yes a very well designed A/B amp will beat an "average"/non optimised class A amp and yes the things you mention (and others) are ultimately more important than class A or A/B. BUT once everything is optimised in these areas where do you go for further improvement? IME a good class A amp has an extra degree of "ease", "liquidity", "spaciousness", "transparency" and timbrel accuracy over a non class A amp.
Class A generally allows the use of vastly less feedback which also goes with all the above benefits and could, arguably, be the biggest benefit from class A!
In areas such as "speed", "PRaT", bass tightness and dynamics I wouldn't expect any benefit from class A... but they are much easier areas to get right anyway.... and much cheaper to get right!

On a brief listen on unfamiliar materiel you would be hard pressed to tell the difference between A and A/B if both done well but further listening with familiar material in more relaxed surroundings would reveal spacial clues, ambience and "spot on violin tone" etc which once experienced it's hard to do without IME. It just sounds less "mechanical" ultimately...
 
Arkless Electronics said:
No it's just class B and one of the worst amp designs I've ever seen going from the schematic...

All down to semantics on the amplifier classes. Class A/B or class A+B? There's lots of other permutations as well.. and check out class S from Sandman which was copied by Matsushita for "class AA". Further confusion arises from class G and class H having opposite meanings depending where in the world you are!! Doug Self wrote an article called something like "class distinctions in audio amplifiers" for those who want to look it up and read further.
Click to expand...


Must admit that my (remaining!) hair stood on end when I saw the linked schematic! I'm not sure I'd have dared to even try something like it's output stages. With complimentary FETs that gave a quiescent, maybe.
 
Disbeliever said:
My integrated Class AB amp is 25 years old and so far the caps have not worn out , do not like Class D or G I have tried many amps including Devialet and can not find an amp that sounds better than my old one.
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Same here.
Have Aragon 2004 and didn't find better sound in D-class, even for triple more money.
 
Arkless Electronics said:
While we are discussing amplifiers what are fishies opinions on the optimum power for a class A amp? Think compromise here! 10W is more than enough if you have Tannoys or Klipsh etc but not much good for small inefficient mini monitors.... For 90dB/W speakers used at "normal domestically acceptable levels" in an average size UK room 10W would still be fine for many people but if you have a large room and like realistic levels obviously again no good....
Price, size, weight and heat start to get silly in class A if one insists on 50W or more.... So where's "the sweet spot"?
Click to expand...

It is my view that the Nelson Pass First Watt amps, all 25-30W/ch Class A, are not quite enough for speakers of average sensitivity. A stout 50W, such as the Pass F5 Turbo 2, begins to reach that area of "authority" and "effortlessness", if you keep to reasonable playback levels.

So, for a real world product, I'd probably cheat and do a "rich" Class AB, such that it's "Class A up to 50W" but then has another 100-200W of headroom on top of that.

(all these numbers assume 8 ohm load)
 
In the past I owned a Plinius SA250 IV. 250W pc in A/B, or switchable to full class A at the same output. That sucker got hot!! Sounded great but I changed it for my bigger MBL’s.
 
Arkless Electronics said:
While we are discussing amplifiers what are fishies opinions on the optimum power for a class A amp? Think compromise here! 10W is more than enough if you have Tannoys or Klipsh etc but not much good for small inefficient mini monitors....
Click to expand...

I’d be perfectly happy with 20 Watts. The thing with inefficient mini-monitors is I’d never want to listen to them loud anyway, so the inefficiency isn’t a handicap. I’m driving my 84db JR149s with my Stereo 20 and they go as loud as I’d ever want a speaker with a 5” bass mid to go. Larger speakers obviously tend to be far more efficient, and if I wanted to listen at high levels I’d not dream of using anything else. Far more important is the ability to drive low impedances etc.

I’ve said it before, but I honestly think there is a market for a 20 Watt Krell type class A amp, i.e. one that keeps doubling down properly to 1 ohm and could contend with even the most obnoxious ported stand-mount or panel without strain. I’m pretty convinced had there been a KSA 20 in the series with the 50 and 100 there would be one in one of my systems. Sugdens are great, but they don’t do the low impedance thing, and I am sure that is what gives Krells their astonishing power, weight and scale even at very low levels.

PS I remember comparing my old Naim 62/140 against a friend’s KSA 100 into Acoustic Energy AE1s and even at low volume the Naim sounded tiny compared to the Krell. It just couldn’t drive these inefficient and I believe very reactive speakers. It wasn’t Watts we were running out of, it has to be low impedance drive. Same scenario if one asks a Quad 303 to go to work much below 8 Ohms!
 
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