Tube Watts vs. Solid State Watts - Any credence?

Geoffkait's dynamic headroom theory falls apart when faced with a class A amplifier, which can be either tube or solid state.

The Dynamic headroom of an amplifier is measured in decibels, and has to do with the class of operation and the amount of energy storage in the power supply. The spec is rarely used today. The more dynamic headroom, the poorer the amp in general; the idea being that if class AB and without much power supply, for a brief instant the amp will be able to make more undistorted power than its constant power spec.

A Class A amplifier will have 0 db of dynamic headroom. A really bad amp will have 3 db of dynamic headroom. The spec was created in the 1970s to make cheap amplifiers look good on paper.

Large headroom doesn't mean poor performance. It means that amp has ability to output higher momentary peaks. Otherwise it is power limited by power supply and/or heatsinks. That's what music is - peaks, gaps and very low average power (few percent of the peak). Power test is done with continuous sinewaves.

I think there have been some designs over the years that advertised large headroom out of a more compact box in particular that were not very good sounding overall on teh grand scale of things. I had a Hitachi Class G receiver for many years that fit this mold.

But I would agree with Kijanki's depiction of headroom.

Soft clipping amps, tube or otherwise are another way to get around the challenge I suppose. Those cannot be accused of having large headroom at higher volumes. They are designed explicitly to LIMIT the headroom in a manner that is not overtly offensive to the listener.

Large amounts of dynamic headroom can be viewed two ways: The amp can put out a considerably greater amount of power for relatively brief periods of time than it is rated to deliver continuously, or the amp can **not** sustain power outputs that are close to its maximum instantaneous capability for longer than relatively brief periods of time.

I agree with Ralph/Atmasphere that in general it would be wise to consider a particularly "good" dynamic headroom spec to be a caution flag.

It's also worth noting that relatively low powered SET amplifiers are often considered to be especially good when it comes to reproducing musical dynamics (due particularly to how their distortion characteristics vary as a function of signal level, as Ralph has explained in the past), yet as class A amps they have zero dynamic headroom.

Best regards,
-- Al

"The amp can put out a considerably greater amount of power for relatively brief periods of time than it is rated to deliver continuously, or the amp can **not** sustain power outputs that are close to its maximum instantaneous capability for longer than relatively brief periods of time."

Al, what's the difference other than worded?

Is there an amp not capable of putting out more power cleanly for a shorter period of time? Soft clipping amps which tend to lessen the need considerably and enable fewer watts to "go further" perhaps?

In any case, one wants to avoid the extra distortion that most amps will produce when pushed hard by not having to run them too hard. I think that's a good rule to follow in all cases.