Most people are interested in the amplifier’s power rating, which is measured in Watts. More watts equals more sound power.

Because music is recorded with Left and Right channels, amplifiers are usually quoted in watts per channel, abbreviated to W/ch.

The most useful power figure you should look for is “RMS power“. *
RMS is a standard, honest way of measuring amplifier power. It’s how much power the amplifier can produce on a sustained basis without distortion.

After power, there are a few other specifications we use to measure amplifiers, the most common one is Distortion (which you’ll see as “THD“, which means Total Harmonic Distortion.) Distortion is an inescapable fact of any kind of electronics that do anything with a signal. The less the better. A theoretically perfect amplifier produces no distortion, but sadly they all do. Though a well-designed amplifier will have distortion figures so low that you can’t hear them.

An interesting aside – In Guitar amplifiers, the distortion is a desired part of the sound, and the amplifiers are deliberately over-driven, so that they distort on purpose. The distortion can fit quite well with the sound and enhance it for the listener in some cases, like an Instagram filter for sound

At ATRAD Audio, we are making amplifiers for hi-fi, not for guitars, so we design and test our amplifiers to minimise any distortions.

* It means Root Mean Squared, a mathematically accurate way of measuring the average power in a varying wave form.