Axiom Home Page Forums General Discussion Technical Questions When is a Watt not a Watt?

Why is it that people seem to say a 5 watt tube amp will power a pair of m22ti speakers fine, but I'm currently running a 75 watt Niles solid state amp to mine with the gains near full, and they're not even close to overpowered. I can't imagine that a 5 watt amp would have the power to even make them audible. 1 watt is 1 watt, right? So how can a tube amp do it?

-Matt (former hardcore lurker)

Matt, the first thing to bear in mind is that at a comfortably loud listening level the power used is typically about 1 watt. Peaks may briefly need 10, 50, 100 watts. So as long as the the music doesn't require very high peak power output, a 5 watt amplifier will be fine. If it gets much beyond that, the amp will distort, although if it's a tube amp the early stages of distortion are less objectionable since it tends to be even order rather than odd order distortion. When high power is required, however, these low-powered amps simply aren't adequate, regardless of what their owners might say.

I've heard that a good tube amp watt is equivalent to something like 3 solid-state watts, but I don't know the reasoning behind those numbers, so don't take it as a fact.

P=V*I doesn't differ from solid state to tube.

generally, most will tell you that one tube watt is equal to twice that in ss watts. And there are also other factors that differ between ss and tube power. my understanding is that tubes can run full power because when they clip its alot more friendly than when ss clips.

Matt, the second thing to bear in mind is that the setting of the level (volume) control is nothing directly to do with the max power output of the amp. The level setting is determined by the sensitivity of your speakers (how loud they play at 1W), the gain of your electronics chain (what input voltage or recorded level is needed to swing the power amp at 1W), and of course, your own listening habits. The maximum available power of the amp does not appear here as a factor.

With regard to the tube amps, it is true that in most tube amps clipping occurs very gradually, and when they start to clip, the quality of distortions is much less objectionable (and much less harmful to speakers because the distortions don't contain much of high-frequency/ultrasonic components). As a result, they produce a quite acceptable sound quality even at way above the rated power.