How Much Amplifier Power Do I Need?

[mixMZ]

Can someone explain me how should we understand how much power amplifier needs from power supply?

let say for example:

Amp Class D
Sure AA-AB32512
http://www.parts-express.com/pedocs...32512-2x500w-audio-amplifier-board-manual.pdf

Output 2x500W @3ohm 48V DC THD+N 10% ,2x270W @3ohm 48V DC THD+N 1%

I found interesting statement on crownaudio website about "How Much Amplifier Power Do I Need?"

How Much Amplifier Power Do I Need? | Crown Audio - Professional Power Amplifiers

and it says: "stay with 1.6 to 2.5 times the speaker's continuous power rating"

That makes me wonder what power supply needs to be used to get such a power from amplifier.

Does it mean that ,if we want to get best quality from example amp - no more than 1% THD ,Amp shouldnt be driven higher than 270W @3ohm and still be higher in power by aprox 1.6 to 2.5 times than speaker power handling? -> then Ideal speaker for that amp should be about 110 - 165W @3ohm per chanel?

spec for that amp says 25 to 50 VDC power supply is required.
Does it mean that if we want to get let say this 270W @3ohm per side ,theoretically we can achieve that from whatever Voltage its in recommended range? P=V*A

And also ,how to convert differences in impedance between amp and speaker?
(if Amp is rated 270W @3ohm what whould be approx. power in 8 ohms?)

Thank you

 

[rayma]

Does it mean that if we want to get let say this 270W @3ohm per side ,
theoretically we can achieve that from whatever Voltage its in recommended range? P=V*A
(if Amp is rated 270W @3ohm what whould be approx. power in 8 ohms?)

You need the formula: Power = Voltage x Voltage / Resistance, where the Voltage is RMS,
a kind of average, and where Vpeak = 1.414 x Vrms. The peak voltage output must be less
than the power supply voltage.

Also Ohm's law V = I x R requires the voltage and current to be related, so we have
P = V x V / R and P = I x I x R. Again, the voltage and current are both RMS,
where (for a sine wave) the peak = 1.414 x RMS.

For your example, 270 = V x V / 3, so V= 28.5. Then into 8 ohms we have the same
output voltage, so 28.5 x 28.5 / 8 = 101.5W.

 

[DF96]

spec for that amp says 25 to 50 VDC power supply is required.
Does it mean that if we want to get let say this 270W @3ohm per side ,theoretically we can achieve that from whatever Voltage its in recommended range? P=V*A

Probably not. 270W into 3R requires an RMS voltage of 28.5V; this is 40.2V peak so will need an amplifier supply a few volts higher - they say 48V. If you only had 40V supply then the AC peak might be 32V or thereabouts which would give you 170W into 3R.

This assumes that the 270W into 3R at 48V supply is voltage limited i.e. the output stage uses up nearly 8V. It could be that the 270W comes from a current limit instead. In any case, the voltage rail sets a limit as peak AC voltage cannot exceed the rail voltage and will usually have to be slightly less than the rail voltage.

 

[woody]

You are asking about what power supply is required for your amp. That article by Crown is not talking about power to an amp but the total power from your amp. You may want to look again at the data sheet. In particular look at the section at the end of the page titled notes. Then in note #8 they recommend a 48v 20.8A power supply. I bet that is a little overkill but that is what the application note says .

 

[PRR]

> not talking about power to an amp but the total power from your amp

Yes; but in good Class D the audio output ought to be 90+% of the DC input. 90% is same-as to the ear.

Speech/music has peaks much higher than average power. It is "usually" the average power which blows-up speakers. We "can" use an Infinite-power amplifier, to ensure unmangled peaks, if the average does not smoke the speaker. That ideal is infinitely expensive. 200W amps on 20W speakers can be quite fine if the average power is kept reasonable.

Crown was addressing the specific economic problem of Commercial Sound. You want to cover the whole crowd with a minimum of investment in speakers and amp-watts. And with "small" clipping, because watts are expensive and an occasional clip is unimportant. They suggest amps rated about twice the speaker rating. More speakers on less watts is not optimum speaker-budget. More watts on less speaker is not optimum watts-budget. Wide variations are possible. I've run 300W speakers on 150W amps, and 75W speaks on 20W amps, when speakers were available and big amps were scarce. I've run 200W amps on 20W speakers but played as-if it was a 20W-40W amp.