Input power vs Output power in pro amps

[morongo]

I asked this question on the Crown forums and it was (understandably) removed with no further explanation (it just dissapeared!).

Here's the thing, the XLS1002 amp is rated at 350W/ch-700W total (Harmon doesn't specify RMS, Peak, or whatever).

The back panel, where you plug in the power, says: 50/60 Hz 175 Watts.

Now I know the line voltage is rated in RMS and if i extrapolate the current (I=P/E) I get:
175/120 = 1.45A, all day long.

Further, class D or not, DriveCore or not, it's been my experience over several decades that it is not possible to get more power out than what goes in, regardless of efficiency claims.

In this case, it looks like: 700W/175W = 4 x 100 = 400% advertised efficiency.

Am I just too old-school to understand new output power ratings? Is it now possible for a 9 pound amp to deliver 700 Watts with only 175 Watts of input?

Maybe electronics have indeed just passed me by after all these years.

Thanks for looking,
Tony

 

[BobK]

It is not possible to continuously output more power than the input, as ypu say. So, no, the laws of physics have not changed.

That said, their rating is probably a peak rating than can be maintained for a millisecond or two. That is not impossible nor is it a useful measure of output power.

Bob

 

[morongo]

Thanks Bob, I just had to get another set of eyes on this as a sanity check.
Maybe someone else who has these amps has a handle on how Crown/Harmon rationalizes these figures.

Tony

 

[Harald Kapp]

Unfortunately no details in the manual

 

[Bluejets]

Thanks Bob, I just had to get another set of eyes on this as a sanity check.
Maybe someone else who has these amps has a handle on how Crown/Harmon rationalizes these figures.

Tony

Might be wise for you to stay away from anything remotely associated with air conditioning. The reasoning there between cooling/heating Kw and motor ratings will do your head in.......

 

[dave9]

Am I just too old-school to understand new output power ratings? Is it now possible for a 9 pound amp to deliver 700 Watts with only 175 Watts of input?

These kinds of amp ratings have been going on for decades, nothing new about it, though if designed with low weight as a criteria, you could get 700W RMS out of something weighing only 9 lbs if it were class D.

 

[morongo]

But could you get 700W out with 175W in? And it's questionable as to whether the output is indeed RMS, Crown doesn't specify.

All that said, Crown has a good reputation for pro-amps. Users don't seem to have performance issues (*I* don't have performance issues), but the numbers they specify just don't add up.

 

[Alec_t]

But could you get 700W out with 175W in? And it's questionable as to whether the output is indeed RMS, Crown doesn't specify.

Yes you could, if 175W in is the RMS rating and 700W out is a transient peak rating. But, as Bob said in post #2, you couldn't get 700W out continuously. So Crown's 700W figure can't be RMS.

 

[Martaine2005]

@BobK ‘ reply. And @Alec_t ’s reply. Yes you can for a millisecond before it blows up. The output is more than likely peak.
ie- max output before self destruction.
I have Crown amps and Numark amps. The Numark are great and powerful. But 1200 W is unrealistic. More like 600w driving it hard or 400w playing all day.
Also, amp specs are deceiving. Total music power, RMS, peak etc. None are generally true. It all boils down to a millisecond before they go bang. Some even advertise 1 or 2 Ohms @ 2000w, but have a minimum impedence of 8 Ohms. Straight away bringing it back to 150 or 200 w. Especially in car audio. Baked beans used to be in a can in a unit of weight. Now, the weight is the product including the can. Hence less. Go figure!.

Martin

 

[Audioguru]

The manual clearly says the total output power is continuous with 0.5% distortion. That is true Watts power, not fake peak Whats.
It produces 215W per channel into 8 ohms, 350W per channel into 4 ohms or 550W per channel into 2 ohms.
When the 2 channels are bridged, its output is 700W into 8 ohms or 1100W into 4 ohms.

It is class-D so it is fairly efficient.
Of course the electricity power it uses is a little more than its total output power. The manual does not show 175W anywhere but a photo of the rear of one of them shows AC 425W at 60Hz. Then the output will be about 2 x 215W into 8 ohms at 0.5% distortion.

 

[BobK]

I can make a device that takes in 175W continuously and outputs 700 Watts RMS for one second out of each 10 seconds.

It is actually energy which must be conserved, not power. And energy is power times time. So my device would take in 1750 Joules every 10 seconds and output 700 Joules.

Bob

 

[Audioguru]

You cannot load extra amplifier power into a huge bucket then release it in a moment to get more power. But Snake-oil salesmen think they can doo dat.

Crown amplifiers have a history with truthful spec's of continuous output power at fairly low distortion. Bridged into 4 ohms the power output of this new amplifier is 1100W at 0.5% distortion. The sales sheet says 2400W but says nothing about distortion.

Guess what? It is not available. Maybe it has a bad bug in its design or maybe it does not meet its spec's.

 

[Harald Kapp]

You cannot load extra amplifier power into a huge bucket then release it in a moment to get more power.

You can. The bucket is called capacitor in our terms. You see them usually in the power supply section of an amplifier . That's what makes these confounding specs of peak power etc. possible.
In terms of continuous (rms) power I totally agree with you. That's the spec one should be looking for. Unfortunately the manual of the crown amplifier is totally unspecific in this point.

 

[Audioguru]

Harald, you are talking about "music power".

The power supply in an amplifier is simple for it to have fairly good voltage regulation. A good transformer and a large enough capacitor.
Peak power is simply double the REAL power. Very distorted power (overdrive) also doubles the REAL power because a squarewave has the original signal power plus a lot of harmonics power.

An amplifier with a cheap power supply (not enough capacitance or a cheap transformer that cannot supply the required current continuously) has "music power" that is the power for only a moment before the power supply voltage sags.

REAL power is continuous power with low distortion. The Crown amplifier in this thread is rated like that.

 

[BobK]

If that is the case, the mandated power consumption sticker on the back in incorrect.

Bob

 

[Tha fios agaibh]

175w input

Thinking of it as "watts input" is a point of confusion.
"175w is a rating of what the circuit was designed to handle under normal conditions.

It does not mean 175w is going "into" the amp. The power cord and transformer can handle much more power for a fraction of a second.

 

[Audioguru]

In the User's Manual 175W is not shown anywhere.
A photo of the highest power amplifier in this range shows its AC input at 425W and the spec's shows its total output of 440W into 8 ohms loads. Maybe it says in tiny writing, "or more depending on the load impedance".

 

[hevans1944]

Geez! Have we regressed to the 1940s, simply replacing the venerable Williamson Class AB vacuum tube audio power amplifier with Class D MOSFET switched power amplifiers... all the while keeping the same hype and snake-oil salesmanship? As Little Beaver would say, "You betchum, Red Ryder!" And don't ferget to buy them's gold-plated RCA connectors and cables for the ultimate in high fidelity listening, youse guys what have Golden Ears.

 

[Audioguru]

Antique vacuum tube amplifiers did not produce almost double the 8 ohm power into 4 ohms then produce almost another double the power into 2 ohms.
I also never saw a bridged vacuum tubes amplifier that produced massive power like this Crown PRO amplifier.
The spec's for this amplifier are truthful, producing continuous power at 0.5% distortion.
Snake-oil salesmen sell home theater and car radios that are rated in momentary "peak" power with massive clipping distortion.

 

[Tha fios agaibh]

Yes, it's marketing that the average consumer falls for. It's similar to how some companies started using "peak horsepower" ratings. Very misleading.

The target market is young people who only seems to care about bragging about the wattage. Many believe their new 200w amp is twice as loud their friends 100w amp, without understanding the law of diminishing returns.

Personally I'd rather brag about low thd than high wattage.