#1
if an amp is 25 watt rms and 40 watt peak...does that make it a 25 or a 40 watt amp?
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#2
It makes it a 25 watt amp, because at 40 watts you're running the amp balls to the wall cranked, which isn't how you normally run an amp.
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#3
Quote by Raijouta
It makes it a 25 watt amp, because at 40 watts you're running the amp balls to the wall cranked, which isn't how you normally run an amp.


Not quite, the RMS rating of an amplifier (this includes power amps for home theaters, car stereos, etc.) is the wattage before natural breakup. In tube amps, that breakup is what is desired by us guitar players, but no one else. For solid sate amps, that breakup isn't very pleasant.
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#4
You can think of the RMS power as that which the amplifier can sustain all day and night. The PEAK power is just that - the absolute maximum that the amp can squeeze out. You would do well to check the wikipedia article en.wikipedia.org/wiki/Root_mean_square and have a bit of a read about what this mysterious RMS measure actually is.

Don't get hung up on power ratings though. 'Loudness' of an amplifier is determined by many other factors, the most significant of which is speaker efficiency (which can range from ~85 dB - 100+ dB at 1W/1m). Also, the components used in the amplifier (such as whether it is a valve or solid state device) have a tremendous bearing on perceived loudness.

Perhaps if you told us which amp you were talking about, we could give more accurate advice.
#5
Since the voltage you're using to power the amp is AC (wall outlet), the voltage, current, and power are all sinusoids. The RMS value is the root mean square of the sinusoidal power, which is an easy way to measure AC power (kind of like an average). The peak value is the power level when the sinusoid is at its maximum value. It will reach the maximum value 60 times in a second, since wall outlet frequencies are usually 60 Hz. In one cycle (1/60th of a second), the power in your amp will go from the maximum of 40 W, to j40 W of reactive power (imaginary), to -40 W, to -j40 W, and back again.

So to answer your question, your amp is a 25 W amp.
#6
Quote by Doodleface
Not quite, the RMS rating of an amplifier (this includes power amps for home theaters, car stereos, etc.) is the wattage before natural breakup. In tube amps, that breakup is what is desired by us guitar players, but no one else. For solid sate amps, that breakup isn't very pleasant.


This is mostly incorrect. Distortion, desired almost exclusively by guitarists, is NOT caused by increasing the 'wattage' (which isn't a word, btw) till natural breakup. Please don't give technical advice if you don't know what you're talking about.

Electrical devices use a power source that is some number of volts, and from the internal transformer there are usually a +/- voltage supply. These are called the voltage 'rails'. If it is a 12V system, you have +/- 12V rails. You achieve distortion by increasing the voltage being output from the system to a level greater than the rail voltage. By doing this, you achieve an effect called 'clipping'. This is where the sinusoidal wave loses its peaks and troughs. because the amplitude of the signal is greater than the amplifier can accurately handle. This creates the 'distortion' sound that we guitarists have grown to love.

Of course, this is the most basic sort of distortion, and there are many other ways to achieve it, but the principle remains the same.
#7
ALthough we do measure the RMS power before breakup that isn't how it's defined. RMS is the AC power required to heat a resistive load the same amount as a DC supply would. With a sine wave the calculus works out that the RMS voltage equals the peak voltage divided by the square root of 2 and the RMS power therefore is peak power divided by 1.4
This however should not be confused with what they call peak power in marketing spiels. In that case it is is the power that the amp can deliver instantaneously without blowing up. That makes the value for peak power whatever the hell they want it to say. Is that "instantaneous" power time duration 1ms or 1 us? Is that "instantaneous" power level calculated using RMS or peak voltage? It means whatever they think they can get away with and therefore really means nothing. Also beware of PMP (peak music power) that you see on some stereos - it means even less.
The RMS power rating is the only power rating that you can take any notice of, everything else is non-sensible gibberish.
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#8
ok thanks for summing that up
King of Shred

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Ibanez SR505
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Line 6 Spider III 75
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ISP Decimator
Laney GS412LA Cab
Peavey VK100