power ratings

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trebejo

power ratings
« on: 29 Jan 2012, 05:10 pm »
Some time ago I remember that I visited the AVA web site and I was informed that the spec game was not for them. Something about it all being a bunch of BS, hijacked from people that meant well by people that only cared about scoring a sale.

Nowadays we all seem to be loving our new 400R/600R amps but I doubt it's all about the watts. I suspect it's all about the high slew rates and low distortion. Why, even the "lowly" 35-watt U70 tube amps that Frank ships out (a natural, sincere evolution from the venerable Dynaco ST-70 push-pull design) sound fanstastic; I loved my U70 during the cool months of the year, and it was only the tube heat that made me put it away.

Yesterday I ran into this essay on what it was that made those hifi pieces from the 1970s great (and sadly I suspect that much of it was that our young ears were in better shape than today, but perhaps this is Mother Nature's way of compensating with dispensible adult cash for the passing of time):

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http://seventiesstereo.blogspot.com/2008/08/power-ratings.html

POWER RATINGS
 I think this FAQ from Legendary Audio Classics is very helpful. It explains why the Sony 20 watt amp I talked about earlier sounds so dynamic:
Why does a 35 watt Marantz sound better and louder than many 100 watt receivers?
A: Because 35 watts/channel as specified by Marantz in the 1970's meant...
" The unit can deliver 35 watts into 8 ohms for one hour, from all channels at the same time, with no significant change in distortion, or other specifications, at any time during, or after, the test hour."
...while 100 watts/channel today (for instance, in my JVC surround system) means...

" The unit can deliver 100 watts for a fraction of a second, in one channel only, if the other channels aren't running and nothing else high energy has happened to drain the power supply of stored energy in the last few seconds."
In fact, my JVC 5-channel Dolby surround receiver claims 500 watts RMS, but the power consumption label on the back panel tells the story:

320 Watts
If my JVC receiver was 100% efficient, meaning that every bit of power it took from the wall was delivered to the speakers as audio power (which it isn't), that'd give you only 64 watts a channel, about 2/3rds of the claimed power rating (which is 100 watts per channel, remember, 500 delivered as 100 per each of the five channels.)

But since the receiver can only (at best) convert about 50% of the available energy to the speakers, and the available energy is what is left over after the heat is generated (did I mention that this model JVC runs almost too hot to touch on top, even when making no sound at all?) and the watts that go to lighting the panel and powering all of the other circuitry are accounted for, the system can perhaps, when brand new, on a good day, generate 32 watts a channel continuously with all the channels going, which is pretty sorry compared to the claimed 100 watt per channel rating. That is less power per channel than an old 2235 receiver. Shocking, eh?

Turning it around, because of the way that the units were rated in the 1970's, that classic 2235 Marantz receiver, rated at 35 watts a channel, can dependably produce much more than 35 watts in both channels at the same time for a minute or two (far longer than the peaks in a modern receiver.) An honest rating for use with music for the power amplifiers of an older Marantz is generally in the range of 120% of rated power or even higher.

These ratings were instituted because of many false claims for power output that were being made using many different types of power measurement and general baloney at that time. IHF, RMS, Peak, Peak Music Power, Average, etc. RMS is what was settled on, and it's still widely used today, but the one hour rating was dropped some time back.

Interestingly, the situation that caused the RMS for one hour ratings to be made standard is now recurring - as I mentioned above, my JVC's ratings are pretty obviously designed to deceive the consumer to an extreme degree. Certainly there is no way that they can claim that those ratings paint an accurate picture of the amount of power the receiver can actually deliver in real world conditions - loud music and cinema surround takes a lot of power, in a lot of channels. Try listening to Jurassic Park... wait till the Tyrannosaur walks up behind you, or there is something exciting going on. Those 32 watts are pretty puny...


To the relatively straightforward power issue, you can add the fact that the design of the audio and RF circuitry in a Marantz is absolutely top-notch, and you can hear that in the character of what little distortion there is, in the way the bass, midrange and treble controls (and loudness contour and filters) affect the signals, in the way the FM signals come out sweet and clean, and so on. As an engineer, I really don't like to drop into using descriptive terms meant for food or lovemaking and so on for sound, but you know, when you A:B a Marantz against other units that are supposedly equivalent, the bottom line is it sounds better, and obviously so.
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Mutatis mutandis, and taking advantage of the inexorable advancement of technology and software, I think the same spirit applies to the AVA pieces I have sitting on the rack today. But the first interesting take away from this is that the wattage is a bit relative and maybe 35 watts is more than enough. The second is that with an outfit like AVA you are obtaining a continuity from that 1970's golden era in the flesh (literally) and in spirit as well, since the transition to mass production and cost optimization balanced on the backs of Jungian marketroids is just not done in AVA.

Just some random ruminations on a morning with no work to do and lots of great music blasting out in the background...

JLM

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Re: power ratings
« Reply #1 on: 29 Jan 2012, 06:50 pm »
All true, but add to that:

Ratings used to be 20 - 20,000 Hz (for years now most vendors only measure at 1,000 Hz when most power is consumed below 100 Hz).

Some vendors "cheat" and rate their amps at 6 ohms (Signalpath - Peachtree for example) or emphasize the 4 ohm ratings so they can publish bigger numbers.

JLM

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Re: power ratings
« Reply #2 on: 29 Jan 2012, 06:57 pm »
Keep in mind too, that how the amp clips will help define "in the real world" how much usable power is available.  "Soft clipping" (a term invented by NAD) applies to NAD, tube, and other designs to describe how the overloaded circuit will react.  OTOH hard clipping results in the cone/dome/etc. trying to instantly stop, which generates lots of heat and is destructive.

Also note that the relationship between watts (electrical power) and dB (what we hear) is logarithmic.  IOW it takes 10 times the power to double the apparent loudness.  So 400 wpc is barely twice as loud as 35 wpc.  But to avoid clipping (especially typical solid state hard clipping) and to provide a commanding grip on the speakers more power is better than less (all other factors being equal).

Wayner

Re: power ratings
« Reply #3 on: 29 Jan 2012, 07:46 pm »
All of this must also take into account speaker type and efficiency and it's reaction  to the amplifier's output.

A classic example of this is the use of super high-efficiency horn type speakers used with SET amps. On the other end of the extreme has to be planar or electrostatic types of speakers, that have impedance ratings the are near zero and suck gobs of power.

On top of all of this is the public's lack of understanding between amplifier requirements and speaker type/efficiency. We certainly don't need a 600R FET Valve amp to run 106db efficient horn speakers.

The other problem is what, in real terms, is considered enough power (to achieve a listening level) that varies from person to person, in various mind sets (even intoxication), that is sustainable.

Wayner

charmerci

Re: power ratings
« Reply #4 on: 29 Jan 2012, 08:26 pm »
This reminds me of the time I was at some fair and I saw a boombox with a sticker that said 1000 WATTS. Next time, I've got to take a picture!

dB Cooper

Re: power ratings
« Reply #5 on: 29 Jan 2012, 08:49 pm »
Apparently the FTC power spec regulations instituted in the 1970s  (referred to by trebejo and also discussed at length in Frank's old Audio Basics newsletters) either don't apply to "home-theatre" audio equipment, or just aren't enforced anymore. My 25WPC AVA Mos-Fet integrated used to drive my inefficient Allison Fours to levels that were hard to converse over in a small-to-medium sized room. Remember, the conventional method used to rate power output basically measures how good your amp is at heating up a resistor using a sine wave source.