American Representation Of Power Rating Of AMPS

[sureesh40]

Hi

I was looking through the specs of a vintage amp and it says the power output is 25 watts RMS per channel and it qualifies this by adding the statement "Measured Pursuant To Federal Trade Commission Regulation Rule On Power Output Claims for Amplifiers"

This is of course an American standard and this is the first time I am seeing such a statement added in with the specification sheet of an amp.

But what I am wondering about is , is there any difference between how power output is measured as per American standards and how it is measured according to British standars. I have never seen any spec sheet of an amp saying the power output claims are as per Brtisih regulations.

 

[wilro15]

I always thought it was down to each manufacturer, rather than country. Some overstate the value while other seem to do the opposite.

It makes it confusing for the customer so that you really must do a lot more research. You can't really compare wattage values, as there are other factors which I don't fully understand myself.

 

[drummerman]

Maybe its a high torque/low peak rev kind of RMS? - Think big V8

 

[drummerman]

I always thought it was down to each manufacturer, rather than country. Some overstate the value while other seem to do the opposite.

It makes it confusing for the customer so that you really must do a lot more research. You can't really compare wattage values, as there are other factors which I don't fully understand myself.

Yes, quoted power in any absence of distortion and frequency figures can be confusing, even misleading but RMS is RMS regardless of what country.

 

[davedotco]

The Federal Trade Commision standards was an attempt to rationalise amplifier specs at a time when amplifier manufacturers were claiming anything, "total peak music power" anyone?

The most contentious issue was power output, specifically what was termed 'preconditioning'. The amplifier would be run at a substantial, one third of rated power for an hour, before measurements were taken. Many amplifiers failed under these conditions due to inadequate power supplies or heat sinking and many more produced only a fraction of their rated power. This included many 'audiophile' amplifiers and virtually all valve and solid state Class A designs.

The industry was in uproar and after a while the FTC regulations were quietly dropped.

On a slightly different subject, the use of dBw(att) as a measure of amplifier power has been proposed on several ocassions. If 0dBw is defined as 1 watt into 8 ohms, then 10 watts would be 10dBw, 100 watts, 20dBw, 1000 watts 30dBw etc.

This give a more acurate representation of the measured output level in relative terms and a reasonable approximation to percieved loudness. Ie an amplifier delivering 13dBw will have twice the power of one delivering 10dBw and one delivering 20dBw will seem twice as loud as the one at 10dBw. Nice and easy to understand, but not 'impressive', so rarely used.

 

[Vladimir]

Most strict were DIN regulations in (West) Germany where each amp by default was tested always at 4 ohms for 2 hours at full power before clipping. Today declared max power before clipping (1% THD) is usually for a short amount of time and you will notice in Stereophile tests few budget amps pass the preconditioning test of 1 hour running at 30% of max output power.

Canada, Germany, UK and others have regulation agencies equivalent of the American FTC. Problem is they fail at protecting consumers form manipulation and scam by manufacturers. Technical specifications today still are selective and incomplete in order to give false impression of higher performance than realistically possible by the unit. If there is a tighter regulation everyone will scream "Communism!", so caveat emptor. *unknw*

 

[jcbrum]

There are many ways to quote amplifier power, and all of them valid. RMS is not particularly useful for replay of music. Peak Power is just as relevant for fidelity.

These days though, when separate amplifiers and passive speakers are falling out of use, it's of little interest.

What most are concerned with is 'how loud does it go', and at what level of distortion.

JC

 

[davedotco]

There are many ways to quote amplifier power, and all of them valid. RMS is not particularly useful for replay of music. Peak Power is just as relevant for fidelity.

These days though, when separate amplifiers and passive speakers are falling out of use, it's of little interest.

What most are concerned with is 'how loud does it go', and at what level of distortion.

JC

Hence the suggestion of the dBw power ratings given above, dBw relate exactly to measured level and very close to percieved loudness.

The difference between a 100wpc amp and a 200wpc amp may sound like a lot stated like that, but in dBw it is the difference between 20 and 23 (dBw), is a relatively small difference in real terms.

 

[drummerman]

There are many ways to quote amplifier power, and all of them valid. RMS is not particularly useful for replay of music. Peak Power is just as relevant for fidelity.

These days though, when separate amplifiers and passive speakers are falling out of use, it's of little interest.

What most are concerned with is 'how loud does it go', and at what level of distortion.

JC

Hi JC

There are quite a few examples of SS amplifiers with higher distortion during the first watts ... right where most folks operate them at.

I would assume that is no different for some actives.

 

[tinkywinkydipsylalapo]

These days though, when separate amplifiers and passive speakers are falling out of use

Only in the dreams of a few. Repeating this mantra over and over again doesn't make it any more true.