I'm trying to understand if there's any relationship between the rated wattage (RMS) of an audio amplifier and the corresponding power requirements on its power supply.

Practically, if I buy an amplifier that does not have its own power supply, is there any formula or inference I can make to help me determine the minimum wattage of the (bench) power supply I should purchase?

To provide an example, consider the following cheap amplifier and a power supply such as this one. Is it powerful enough? Not powerful enough? How can I tell?

1 Answer 1


your amplifier is capable of delivering 240 Watts of energy.

Power (Watts) = Voltage (volts) x Current (amps)

Therefore the current range is:

Power/Voltage = Current

  • 240 W / 12 V = 20 A
  • 240 W / 26 V = 9 A

So when powering the amplifier from a higher voltage, you are likely to require less overall current.

Maximum current drain at maximum power is 20A

The amplifier board indicates 90% efficiency, so you may well need to factor this in:

  • (240/12)/0.9 = 22

So in order to deliver 240 Watts you may need to supply 22 Amps.

Looks like that PSU will probably be good enough to power that amplifier board.

  • Thanks Mark, your caclulations seem straightfoward and easy to understand. I think, as in many things, these are all in a sense "worst case scenarios", in that the amplifier won't be delivering peak power 100% of the time, or for very long, so these are "safe" maximums, is that an accurate statement?
    – Tom Auger
    Nov 21, 2018 at 16:25
  • 1
    Yes. That is an accurate statement. Note in the specs the difference between "peak" output and "RMS" output. RMS is "square root of mean of squares of instantaneous values".
    – Mark
    Nov 22, 2018 at 2:53

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