Tube Watts vs. Solid State Watts - Any credence?

I have a 500 w/ch Class D amp. Class D is a different beast. It is designed to deliver the power only as needed as I understand it. That's what enables it to be small powerful and energy efficient. It never breaks a sweat or sounds strained at ANY volume, is as musical as anything I hear. It also soft clips to boot I believe. I've never heard anything less than lovely come out of these.

I'd compare that to my old Hitachi SR804 Class G 50 w/ch amp that advertised 100 w/ch headroom as I recall. This was quite midfi at best in comparison but a very nice looking unit with a very good tuner. My conclusion is that switching technologies that enable such things have come a long way and are now capable of doing things as well as most anyone might expect or need.

I also have a 60 w/ch Class D integrated with next generation Class D technology in it. htis does not go as loud but does exceptionally well, the best 60 watts out of an integrated amp I have ever heard by far.

Tell us, once more, about Ohm speakers mapman
It's been at least 2 days
Yawn.........................

Al and Ralph ... help me with the terminology. When I think of headroom, I think of an amp's ability to handle short term dynamic transients, which is part of real music ... especially classical music.

To be more specific, my tube amp has a 1040 joule power supply. In my "un-technical" way, I interpret that as "head room" because my amp presumably can handle short term power demands that exceed its rated power output of 150 wpc, subject to FR, speaker impedance and tap output impedance. Am I mixing and matching terms and concepts here??

ss watts can be misunderstood as well. "Qaulity" watts matter more than quantity. The more important consideration if the amp's ability to drive a low impedance load and remain dynamically stable. Thus the power supplies are critically important. You want a large, highly efficient multi-regulated power supply with a high current and a good damping factor. For example, my Vitus SIA-025 has 'only' 25 watts kl.A power & 100 watts kl.A/B (switchable), but has a very efficient 1.4kVa UI-core transformer which is capable of controlling low impedance loads running in kl.A mode. Big transformers also tend to be heavy, and the SIA-025 weighs 42kg. Compare that to the Accuphase E-600 which weighs 24.7kg. I can't think of any other class A ss which integrated amp which can do that. Similarly tube amps can have some pretty hefty transformers. I know the Absolare 845 mono blocks were driving the S5's comfortably at CES last year.

Bruce (Bifwynne), from John Atkinson's measurements of your ARC Ref-150:

All taps behaved similarly when it came to the maximum output power. Into a load twice the nominal tap value, the Ref150 clipped (defined as 1% THD) at 90W (19.6dBW, fig.4). Into the nominal tap value, it clipped at the specified 150W (21.75dBW, fig.5), but with a higher level of distortion. Into half the tap value, the amplifier clipped at 80W (13dBW, fig.6), but with even higher distortion at lower powers. It is important, therefore, to use the transformer tap that best matches your preferred loudspeaker.

And from ARC's specs for the amplifier:

150 watts per channel continuous from 20Hz to 20kHz. 1kHz total harmonic distortion typically 0.6% at 150 watts, below 0.03% at 1 watt. Approximate actual power available at ‘clipping’ 160 watts (1kHz). (Note that actual power output is dependent upon both line voltage and ‘condition’ i. e.: if power line has high distortion, maximum power will be affected adversely, although from a listening standpoint this is not very critical.)

So since the spec for the clipping point (presumably corresponding to the amp's maximum instantaneous power capability, for some reasonable amount of distortion) is negligibly higher than its maximum continuous power capability, the amp's dynamic headroom is close to zero.

The way to look at it is that the very high energy storage capability of its power supply helps the amp to achieve a continuous power rating that is close to its clipping point, rather than being significantly less than its clipping point (as it would tend to be in the case of an amp having a significantly less robust power supply). As well as perhaps providing other benefits, such as minimizing the extent to which the perceived dynamics of the amp might be compromised by sluggish responsiveness of the AC supply to abrupt increases in demands for current.

Note Ralph's earlier statement 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." Or putting it the other way around, if class AB and without much power supply, the constant power spec will be much less than what the amp can supply for a brief instant.

Best regards,
-- Al