How many watts per channel are enough?

I also agree with Zd542. Watt ratings of amplifiers is like horsepower ratings of cars. It is tricky.

You'll be fine on most recordings with 34 watts, but not on some recordings. And I suspect that a major reason for the diversity of opinion in the previous responses is that people listen to different kinds of music.

Given that your listening is at "low to moderate" levels, the most significant variable is likely to be the DIFFERENCE in volume between the loudest notes and the average notes on the recording. Some well engineered classical recordings which use minimal or no compression will have a ratio of peak to average volumes in the vicinity of 30 db, which means that 1,000 times as much power will be required for brief volume peaks as for the average volume level of the recording.

Most rock recordings, on the other hand, are compressed such that less than 10 times as much power is required for volume peaks as for the average volume level of the recording.

Neglecting room reflections, it can be calculated that at a centered listening position 10 feet from the speakers 34 watts into your 89 db speakers will produce a sound pressure level (SPL) of about 100 db, assuming the specs are accurate. Averaged over a broader set of positions, but at that same 10 foot distance, the corresponding figure is 97 db. "Moderate volume" probably means an average SPL in the area of 70 to 80 db. Many of the symphonic classical recordings in my collection that are especially well engineered, meaning in particular that they are minimally compressed, will reach SPLs of 100 to 105 db at my listening position on brief volume peaks, when played at that kind of average level.

Finally, it appears that although your speakers are nominally rated at 8 ohms, they reach a minimum impedance of 4.1 ohms at some frequencies. That will further reduce your chances of success with a marginally powered tube amp.

Hope that helps. Regards,
-- Al

I don't know if this is of any use to you but here is a amp power calculator. Maybe someone can chime in on what the recommended amount of headroom in db should be.

http://www.crownaudio.com/elect-pwr-req.htm

Thanks, Wilson667. It should be noted that the Crown calculator applies to one speaker, not two. The results it gives are consistent with the calculations I provided above when extrapolated to two speakers, and assuming 0 db headroom.

I would not count on headroom specs, if provided for the particular amplifier, to be either meaningful or helpful. The amount of time that the specified headroom can be sustained for is not usually indicated, and can be expected to vary widely depending on the particular manufacturer's approach to "specmanship." Also, sound quality may degrade significantly at power levels in that region, to a greater or lesser extent depending on the particular design.

Regards,
-- Al

I want to thank everyone very much. I decided to give the Prima Luna a try. I have a 14-day audition period. I am purchasing it from Kevin at Upscale Audio, who based on my due diligence has an excellent reputation. He would be surprised if the 34 watts are not sufficient.

The Prima Luna website explains, "if two amps are . . . both . . . using a pair of KT88 tubes per channel, how can one be rated at 40 watts per channel, the other at 80 watts per channel? This is a simple engineering and math question, and these are the two possible answers:

The higher powered amp isn't really meeting it's specified power rating and/or the tubes are being run very hard to get that extra power. . . .

The benefit of doubling power from 40 watts to 80 watts will only increase maximum volume levels by approximately 3dB."

That makes a lot of sense.