Power of Audio Amplifier?

[cupoftea]

Hi,
If someone tells you that an Audio amplifier has a load of 30 Amps at 120Vrms, then what would be the power drawn from the supplying power supply? The power supply provides a DC rail of 175VDC to the Amplifier. Its for a Bass amplifier.

Also, at one point, he described to me that a different amplifier was a constant load to the PSU......that must mean that that one was a class A or B amplifier?
A class D amp could surely never be a constant load? (playing music, or guitar)

 

[crutschow]

If someone tells you that an Audio amplifier has a load of 30 Amps at 120Vrms, then what would be the power drawn from the supplying power supply?

Yes.
But where would you find a 30A, 120Vac outlet?

he described to me that a different amplifier was a constant load to the PSU......that must mean that that one was a class A or B amplifier?

The would be Class A.
Class B draws much less power with no output signal.

 

[KlausST]

Hi,

30A x 120V = 3600W = load power

30A x 175V = close to DC power (assuming class AB or B)
Indeed one has to define what the 30A are. 30A RMS sine. Or 30A peak or random music.
So let´s say RMS sine.
But you don´t use RMS value when you calculate with DC voltage. Use average. in this case rectified average.
RMS sine --> rectified average is a factor of 1.11.
So divide 30A by 1.11 and get 27A.

..and I doubt it draws the same current even without sound.

Klaus

 

[cupoftea]

But where would you find a 30A, 120Vac outlet?

Thanks, but sorry, i should have said, i think the 120VRMS was referring to the voltage across the coil of the speaker....these audio people seem to have their own way of referring to power.

 

[danadakk]

Basic way to get at Power in is to divide Power out by fractional efficiency.


Regards, Dana.

 

[cupoftea]

I was told that the offline PSU that supplied this "30Amp, 120Vrms" amplifier had a switching frequency of 64kHz, used IGBT's in the primary side, and that there was absolutely no primary side current limiting. I only saw the PCB for a matter of seconds. I was told that there were two opto drivers, so presumbaly two hi side IGBTs....i didnt think opto drivers could do 64khz, at least, not many of them.