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benareeno
Joined: 22 Mar 2006
Posts: 1614
Location: ottawa, canada
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| Posted: Tue Mar 15, 2011 7:12 pm Post subject: what does pure class-a mean to an audiophile? |
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I'm trying to find a nice vintage receiver that I can perhaps hook up a turntable to...I found this Luxman r-404 which appears to fit the bill.
Are current receivers not pure class-a? Is this a better quality amp design than an older Harman Kardon, for instance?
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Curt Palme
CRT Tech
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| Posted: Tue Mar 15, 2011 10:00 pm Post subject: |
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what does pure class-a mean to an audiophile?
Well to me it means that he's an audiophile, of true A(hole) grade, and there's no reasoning with him.
(sorry, I had to!  )
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dturco
Joined: 06 Feb 2009
Posts: 3778
Location: Eastern Shore Maryland
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| Posted: Tue Mar 15, 2011 10:25 pm Post subject: |
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Here is a long explanation, pretty good at describing the mechanics of it.
http://sound.westhost.com/class-a.htm
There is a chart in there showing what kind of power you need to get to 100db. It is less than 35 watts. Most decent class A/B power amps stay below 25 watts for most peoples listening levels. Many of the A/B amps also stay class a the whole time the output is below 16 watts.
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
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| Posted: Tue Mar 15, 2011 10:49 pm Post subject: |
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More seriously, I know Technics made some consumer integrated amps in the mid 80s that I think had Class A at low power, then switched to AB at higher power. Sumo (now out of business) made some decent pure Class A power amps if a pre/power amp combo isn't out of the question for you..
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Tom.W
Joined: 09 Mar 2006
Posts: 6635
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ecrabb
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Joined: 13 Mar 2006
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| Posted: Tue Mar 15, 2011 11:11 pm Post subject: |
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| dturco wrote: | | There is a chart in there showing what kind of power you need to get to 100db. It is less than 35 watts. |
Yeah, but if you keep reading, you'll see the 35w figure isn't real-world - it assumes a 1m listening distance. I don't know about you, but I don't sit 1m from my speakers. More like 3m... Now, we're talking 150w... That right there is why receivers aren't usually adequate for high-performance HT - especially one with acoustic treatments. Back to the article...
| Quote: | | This is not good news for the most part, as it clearly shows that vast amounts of power are needed to achieve a realistic SPL in a typical listening environment. Remember that the figures shown are at a distance of only one metre - the SPL will fall by a further 6dB each time the distance is doubled. (Mind you this is a theoretical figure, which is generally not met in practice - perhaps 5dB would be closer to the truth?) |
Then, if you read further, he gets into the concept of headroom to reproduce transients (dynamic range):
| Quote: | | Realistic SPL in this context is worthy of a page (book?) in itself, but remember that for an average SPL of (say) 85dB, transients will require between 10 and 20dB of headroom. This means that the peak power needed will be between 10 and 100 times the power needed to reproduce the average of 85 dB. At a distance of 2 metres, something around 3 Watts will be needed for this example. To reproduce the transients, the actual power needed must be between 30 and 300 Watts! |
This is what people don't understand. If you turn an amp down to where you can easily speak over it, most amplifiers will sound the same, whether you're talking about a $100 car audio amp or a $3000 Bryston. Good luck telling the difference. But, when you start turning it up to real listening levels, the men get separated from the boys. This is when the low-power amplifiers fall apart.
A small amp (a receiver for instance) might sound fine ok 80dB because like you said, it only takes a small fraction of the amp's power to drive that SPL. But, that only holds true as long as the source material doesn't have much transient dynamic range! If it's nothing but a vocal, you're probably fine. Throw in a piano and an upright bass with the vocal, or a symphony orchestra with a tympani and a string section and now the dynamic range is so compressed it sounds like a mushy mess.
I learned about dynamic range compression first-hand when I went from driving my mains with a 100w Marantz receiver to driving them with a Crown pro-sound amp pushing about 300w. The sound was identical if you turned it down, but crank it up to 85-90dB, and the difference was MASSIVE.
Amp power is like horsepower - there is no substitute.
SC
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Curt Palme
CRT Tech
Joined: 08 Mar 2006
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Location: Langley, BC
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| Posted: Tue Mar 15, 2011 11:16 pm Post subject: |
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Keep in mind as well that speaker efficiency plays a big part with how much power you need. That's why the old horn loaded speakers from the 50s and 60s (and later) sounded so good with small amps. With 100+db 1 watt/1m, a 10-20 watt RMS amp was plenty.
Speakers like Bose are super inefficient, but due to power (with AB amps) being dirt cheap these days, you can sacrifice speaker effieiency.
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dturco
Joined: 06 Feb 2009
Posts: 3778
Location: Eastern Shore Maryland
TV/Projector: Runco DLP VX-3000i Marquee 9500 parts doner
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| Posted: Tue Mar 15, 2011 11:25 pm Post subject: |
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3% distortion at 90 watts. 145 degrees operating temp, 300 watts of electricity input to get 1/3 the power out.
But I bet it sounds sweet 
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dturco
Joined: 06 Feb 2009
Posts: 3778
Location: Eastern Shore Maryland
TV/Projector: Runco DLP VX-3000i Marquee 9500 parts doner
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| Posted: Tue Mar 15, 2011 11:40 pm Post subject: |
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| Quote: | I learned about dynamic range compression first-hand when I went from driving my mains with a 100w Marantz receiver to driving them with a Crown pro-sound amp pushing about 300w. The sound was identical if you turned it down, but crank it up to 85-90dB, and the difference was MASSIVE.
Amp power is like horsepower - there is no substitute.
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All of this is true 300w is where the real play is at. But for just 2 Channel listening a class A amp has a unique sound. I like to say a sweet sound, honey coated and dripping with character.
So for this point class A is just a tool for getting a specific type of sound not a high SPL sound.
Should we talk about tube amps too?  I 'll go get out my audiofool thesaurus. 
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kal
Forum Administrator
Joined: 06 Mar 2006
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Location: Ottawa, Canada
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| Posted: Wed Mar 16, 2011 1:36 am Post subject: |
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| Curt Palme wrote: | Keep in mind as well that speaker efficiency plays a big part with how much power you need. That's why the old horn loaded speakers from the 50s and 60s (and later) sounded so good with small amps. With 100+db 1 watt/1m, a 10-20 watt RMS amp was plenty.
Speakers like Bose are super inefficient, but due to power (with AB amps) being dirt cheap these days, you can sacrifice speaker effieiency. |
Yup. Even today you'll find audiophiles with GIANT horn spears driven by 8W/ch single triode tube amps.
Kal
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mr_ro_co
Joined: 08 May 2006
Posts: 1643
Location: Santa Fe NM
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| Posted: Wed Mar 16, 2011 3:57 am Post subject: |
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| ecrabb wrote: | This is what people don't understand. If you turn an amp down to where you can easily speak over it, most amplifiers will sound the same, whether you're talking about a $100 car audio amp or a $3000 Bryston. Good luck telling the difference. But, when you start turning it up to real listening levels, the men get separated from the boys. This is when the low-power amplifiers fall apart.
A small amp (a receiver for instance) might sound fine ok 80dB because like you said, it only takes a small fraction of the amp's power to drive that SPL. But, that only holds true as long as the source material doesn't have much transient dynamic range! If it's nothing but a vocal, you're probably fine. Throw in a piano and an upright bass with the vocal, or a symphony orchestra with a tympani and a string section and now the dynamic range is so compressed it sounds like a mushy mess.
I learned about dynamic range compression first-hand when I went from driving my mains with a 100w Marantz receiver to driving them with a Crown pro-sound amp pushing about 300w. The sound was identical if you turned it down, but crank it up to 85-90dB, and the difference was MASSIVE.
Amp power is like horsepower - there is no substitute.
SC |
This is a very complicated subject. It is not merely about power. Class A amps typically sound better, often much better, for many reasons. And despite what you claim, the differences can still be heard at low playback levels. Especially in the case of the Pass Labs, which is not push-pull and has both the even and odd distortion harmonics in its distortion spectrum. Topology matters. How many gain stages the amp has, how much feedback, how much inter-gain stage FB and global FB, all this impacts distortion spectra. And class A amps also usually have the output sections and power supplies that allow them to mimic true voltage sources. One sort of follows the other. This is a very big deal, because it means the speaker is not current limited. It takes a lot of money to produce such amplifiers, and they most certainly sound better. And they tend to be much more transient stable, that is, the way distortion follows power dissipation is less unruly than with 5 gain stages and lots of GNF.
Crown? Good equipment, for sure. But I will tell you, once I'd convinced myself that that the Crown Macro (500W/ch into 8 ohms) was THE sh*t, I put back the KSA 250 (this was back in 1992) and let me tell you: The Krell DEMOLISHED the Crown.
The fact that the Crown had a 2000W transformer (or something like that) in it and the Krell had a 4500W transformer in it should be illustrative why. The Krell, although half the power into 8 ohms on paper, is a voltage source. The Crown is not. And the Krell was class A up to 100W/ch. Can't remember what the Crown did, but the design topology between them is quite different, which means the distortion spectra of each is different. At all power levels.
Amps with big rails (70VDC) usually do "wake up" the typically abysmally inefficient speakers (assuming wide bandwidth ability which gives you the fast rise time and "crest factor"), but topology still really matters, because big rails in isolation say little about voltage sourcing capability and distortion and noise spectra, which is a function of power supply design and amplification topology.
Steve
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benareeno
Joined: 22 Mar 2006
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Location: ottawa, canada
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| Posted: Wed Mar 16, 2011 5:26 am Post subject: |
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all good stuff...and good to know because I don't particularly care for high spl...in fact, I am quite often annoyed by movies with too much dynamic range!
I love movies with great musical soundtracks and clear dialog...not really caring for explosions or other annoying scenes.
I had a harman receiver in the late 80's early 90's and was encouraged to pair it up with 4 ohm speakers because the high current design would come into play and the result would be a dynamic sound without distortion from amp clipping. I had previously had a Sherwood receiver and the upgrade was basically huge! Even at moderate volume the Harman was more solid...hard to quantify, but it was just better.
I might start another thread to see if someone can help me repair an old Harman receiver with no left channel and a finicky power switch...
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Tom.W
Joined: 09 Mar 2006
Posts: 6635
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| Posted: Wed Mar 16, 2011 5:27 am Post subject: |
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Kim should have some thoughts on all this....
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mr_ro_co
Joined: 08 May 2006
Posts: 1643
Location: Santa Fe NM
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| Posted: Wed Mar 16, 2011 3:11 pm Post subject: |
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| kal wrote: | | Curt Palme wrote: | Keep in mind as well that speaker efficiency plays a big part with how much power you need. That's why the old horn loaded speakers from the 50s and 60s (and later) sounded so good with small amps. With 100+db 1 watt/1m, a 10-20 watt RMS amp was plenty.
Speakers like Bose are super inefficient, but due to power (with AB amps) being dirt cheap these days, you can sacrifice speaker effieiency. |
Yup. Even today you'll find audiophiles with GIANT horn spears driven by 8W/ch single triode tube amps.
Kal |
This applies only for simple SPL absolutes. As strange as it may seem, high current, class A amps with big rails benefit highly efficient speakers just as they do with standard inefficient speakers, even though you'll never use more than 1~2 Watts of the 200~500/ch you may have on tap. I know that sounds ridiculous, but it's absolutely true.
Consider the 3+ OHMS of output impedance an 8W SET amp of meager bandwidth (100Hz to 10KHz). And the noise, holy hell, the noise from those amps. You can hear it 50' away with horn speakers. Huge amounts of timber eq by virtue of gobs of even order harmonics does sound glorious, though.
It's a good thing to put a wide bandwidth, low output impedance amp with 70 volt rails on a 110dB/2.83/1M speaker. Believe it.
Steve
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beun
Joined: 28 Jun 2006
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| Posted: Wed Mar 16, 2011 6:24 pm Post subject: |
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I can definitely add to the confusion if need be. From an engineering point of view class A is nice although a bit wasteful. The problem driving real speakers is the limited current drive in one direction leading to the danger of asymmetric current clipping into low impedances. A well engineered class AB push-pull does not have this issue as much.
Although I agree with the statement that air pressure is a single ended phenomenon I don't agree with the conclusion that therefore the amplifier can be single ended as well. To me this sounds too much like piling error upon error, in order to perfectly represent a single ended quantity it it best to use a push-pull system.
Talking about power specs is a nightmare, RMS power (in what impedance), peak power (for how long), program power (who knows what I am going to listen to next) etc. If any power is spec'd it should use the RMS measurement method and I like to see in in 2, 4 and 8 Ohm impedance, that at least gives me an indication of the current drive capability. It would also be nice to mention if that power can be delivered continuously or if my amp is going to die of heat stroke.
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Curt Palme
CRT Tech
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| Posted: Wed Mar 16, 2011 7:41 pm Post subject: |
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To add what Beun says, despite the claims of amp manufacturers (esp with car stereo!) to drive 2 or less ohm loads, I think you're asking for trouble if you go under 4 ohms, Amps run red hot, so I always stick with 4 ohm loads or higher.
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mr_ro_co
Joined: 08 May 2006
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Location: Santa Fe NM
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| Posted: Thu Mar 17, 2011 2:58 pm Post subject: |
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| beun wrote: | I can definitely add to the confusion if need be. From an engineering point of view class A is nice although a bit wasteful. The problem driving real speakers is the limited current drive in one direction leading to the danger of asymmetric current clipping into low impedances. A well engineered class AB push-pull does not have this issue as much.
Although I agree with the statement that air pressure is a single ended phenomenon I don't agree with the conclusion that therefore the amplifier can be single ended as well. To me this sounds too much like piling error upon error, in order to perfectly represent a single ended quantity it it best to use a push-pull system.
Talking about power specs is a nightmare, RMS power (in what impedance), peak power (for how long), program power (who knows what I am going to listen to next) etc. If any power is spec'd it should use the RMS measurement method and I like to see in in 2, 4 and 8 Ohm impedance, that at least gives me an indication of the current drive capability. It would also be nice to mention if that power can be delivered continuously or if my amp is going to die of heat stroke. |
Class A is certainly the least efficient, but it gets rid of the biasing switching distortion in A/B.
I agree with the false analogy of single ended amps and air pressure. That's not the reason to go with single ended amplification. The reason is an intrinsic distortion spectrum that favors odd order harmonics over the dissonant odd order components. Push pull automatically gets rid of most of the even order, then innerstage and global negative feedback is usually applied to reduce the odds and output impedance. So you are left with reduced dissonant odd order distortion products. If you have a single ended amp with a more easy-on-the-ears spectrum of acceptable levels with no feedback and reasonably low output impedance without feedback, what's not to like? Especially if it can deliver current unhindered. Of course these amps are very heavy, very expensive, very hot, and power wasteful.
This is not to say class A/B amps of modest traditional push-pull design can't sound great. They just aren't as good as the arc welding class A.
Yes, I agree power should be stated RMS into 8, 4, 2, and even 1 Ohm, which would tell us the current limiting (or lack of) we will experience with an amp. This is important since typical 8 ohm speakers have an impedance modulus that can dip below 4 ohms, sometimes with a punishing phase angle. Basically, every affordable consumer power amp is current limiting the speaker to some degree, even with "8" Ohm loudspeakers. The compresses dynamics variably as function of the speaker's impedance curve. This can only be overcome with true voltage source amps, and this comes at a very high price.
Steve
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