The power cords on most amps are based on their rated power output at 8 ohms. Even then, this doesn't mean that the cord that was supplied is adequate for what the amp is capable of.
As speaker impedance is dropped, most amps will draw more power as they try to put out more power. As such, it is quite possible for a good sized unit to draw more than 15 amps. As an example, let's use the very efficient Sunfire amplifier as a reference point.
At 8 ohms, the "standard" 2 channel Sunfire is rated at 300 wpc @ 8 ohms, 600 wpc @ 4 ohms and 1200 wpc @ 2 ohms. When tested by a third party reviewer, this amp actually delivered 387 wpc @ 8 ohms, 768 wpc @ 4 ohms and 1460 wpc @ 2 ohms. These readings were taken on a steady state basis i.e. clipping and not a temporary "peak" reading. Peak power would be even higher but for a much shorter duration. As a side note, power output at clipping is the truest way to tell just how well built and stable an amplifier is. This one obviously passes with flying colours.
Obviously, these figures are quite respectable and "almost" a perfect voltage source. Given that this is a stereo unit, it is actually putting out twice that amount of wattage as you have two channels. This means that the amp can, if called upon to do so, deliver almost 3000 watts of output at low impedances. Since all amps draw more power than they put out, one can see that if one were standing on the throttle of a very low efficiency low impedance speaker that could handle gobs of power, it is possible to pull WAY more than what a 15 amp circuit is rated to deliver. Granted, this would be a rare occurance to ever need this much power, it doesn't mean that the amp couldn't take useful advantage of having this much power available to it at any given time.
What happens when we need high current from the wall and we can't get everything that we need? It's simple. The voltage rails on the amp sag, power output falls and distortion occurs. This is a form of dynamic compression and is a non-linear distortion. By non-linear, this means that the distortion doesn't occur all the time, only during given conditions ( like peaks ). As such, if we can provide the amp with a very high and steady voltage, we can count on the amp to deliver the goods in the best way that it can and do so in both a steady state and peak manner.
Now take all of this a step further. What does one get when one runs a high powered multi-channel amp for HT and / or multiple amps for two channel? You can end up with quite a bit more draw. On top of this, most amps aren't anywhere near as efficient as the Sunfire amps, making them "gulp" down power whereas the Sunfire would be "sipping" from the AC line as needed.
As as side note, the "Kill A Watt" device mentioned above works only when testing devices that pull a steady state load. In other words, one can test their system at idle OR when playing music IF the amp is of a true Class A design. Given the dynamic nature of music and the dynamic draw of power from the wall to reproduce it, the "Kill A Watt" isn't fast enough to actually measure and respond to the changes as they occur. As such, if you use one of these devices to check what your system is playing as you normally use it, the readings will be measurably lower than what you are actually pulling. As such, if one were to test the Kill a Watt with a light bulb, the readings would be close enough for a guesstimate. With an audio system under a dynamic load, the readings are near meaningless. This is not to say that you can't check individual components to see what they are pulling at idle, but that one shouldn't rely on this device for accurate "in use" readings while "jamming". Sean
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PS... I had driven my Sunfire Signature, which is rated for 600 wpc @ 8, 1200 wpc @ 4 and 2400 wpc @ 2 ohms into thermal shutdown on a couple of different occassions. I was using a 4 ohm speaker with multiple woofers. As such, one can see that it is possible to pull GOBS of power, not only from the amp, but from the wall too. After sending the amp back to Sunfire for some upgrades and circuit changes, i've yet to have the amp shutdown on me again.
As speaker impedance is dropped, most amps will draw more power as they try to put out more power. As such, it is quite possible for a good sized unit to draw more than 15 amps. As an example, let's use the very efficient Sunfire amplifier as a reference point.
At 8 ohms, the "standard" 2 channel Sunfire is rated at 300 wpc @ 8 ohms, 600 wpc @ 4 ohms and 1200 wpc @ 2 ohms. When tested by a third party reviewer, this amp actually delivered 387 wpc @ 8 ohms, 768 wpc @ 4 ohms and 1460 wpc @ 2 ohms. These readings were taken on a steady state basis i.e. clipping and not a temporary "peak" reading. Peak power would be even higher but for a much shorter duration. As a side note, power output at clipping is the truest way to tell just how well built and stable an amplifier is. This one obviously passes with flying colours.
Obviously, these figures are quite respectable and "almost" a perfect voltage source. Given that this is a stereo unit, it is actually putting out twice that amount of wattage as you have two channels. This means that the amp can, if called upon to do so, deliver almost 3000 watts of output at low impedances. Since all amps draw more power than they put out, one can see that if one were standing on the throttle of a very low efficiency low impedance speaker that could handle gobs of power, it is possible to pull WAY more than what a 15 amp circuit is rated to deliver. Granted, this would be a rare occurance to ever need this much power, it doesn't mean that the amp couldn't take useful advantage of having this much power available to it at any given time.
What happens when we need high current from the wall and we can't get everything that we need? It's simple. The voltage rails on the amp sag, power output falls and distortion occurs. This is a form of dynamic compression and is a non-linear distortion. By non-linear, this means that the distortion doesn't occur all the time, only during given conditions ( like peaks ). As such, if we can provide the amp with a very high and steady voltage, we can count on the amp to deliver the goods in the best way that it can and do so in both a steady state and peak manner.
Now take all of this a step further. What does one get when one runs a high powered multi-channel amp for HT and / or multiple amps for two channel? You can end up with quite a bit more draw. On top of this, most amps aren't anywhere near as efficient as the Sunfire amps, making them "gulp" down power whereas the Sunfire would be "sipping" from the AC line as needed.
As as side note, the "Kill A Watt" device mentioned above works only when testing devices that pull a steady state load. In other words, one can test their system at idle OR when playing music IF the amp is of a true Class A design. Given the dynamic nature of music and the dynamic draw of power from the wall to reproduce it, the "Kill A Watt" isn't fast enough to actually measure and respond to the changes as they occur. As such, if you use one of these devices to check what your system is playing as you normally use it, the readings will be measurably lower than what you are actually pulling. As such, if one were to test the Kill a Watt with a light bulb, the readings would be close enough for a guesstimate. With an audio system under a dynamic load, the readings are near meaningless. This is not to say that you can't check individual components to see what they are pulling at idle, but that one shouldn't rely on this device for accurate "in use" readings while "jamming". Sean
>
PS... I had driven my Sunfire Signature, which is rated for 600 wpc @ 8, 1200 wpc @ 4 and 2400 wpc @ 2 ohms into thermal shutdown on a couple of different occassions. I was using a 4 ohm speaker with multiple woofers. As such, one can see that it is possible to pull GOBS of power, not only from the amp, but from the wall too. After sending the amp back to Sunfire for some upgrades and circuit changes, i've yet to have the amp shutdown on me again.