Tube Amps Watts vs SS amp

A pair of those big 600 watt ARC mono amps would be great with the AR9's - but at what cost! 

@bestbaker, as mentioned earlier the speakers are spec’d at 87 db/1 watt/1 meter, with an impedance of 4 ohms nominal and 3.2 ohms minimum. A brochure I found at HiFiEngine.com indicates that an input of 8 watts will produce 96 db at 1 meter, which is precisely consistent with the 87 db/1 watt number. I couldn’t find an impedance curve for the speaker, though, which would indicate how its impedance varies over the frequency range.

**If** the 87 db and 96 db specs are accurate (and speaker efficiency and sensitivity specs are often optimistic by a few db) it can be calculated that at a listening distance of say 12 feet in a medium to moderately large size room two such speakers driven by say 50 watts will be capable of generating an SPL at the listening position that is in the mid to upper 90s. That will be enough volume for most listeners with most or all of their recordings, but it will certainly not be enough for some listeners with some recordings. Especially recordings having particularly wide dynamic range (i.e., a large **difference** in volume between the loudest notes and the softest notes), such as many well engineered minimally compressed classical symphonic recordings.

What may be a more significant concern, though, (which Millercarbon alluded to in his post early in this thread) is impedance compatibility. The speakers were presumably designed with the expectation that they would usually be driven with solid state amplification, and solid state amplifiers almost always have output impedances that are a tiny fraction of an ohm. While the output impedance of tube amps varies widely, and can be anywhere from somewhat less than an ohm to several ohms or more. If the impedance of the speaker varies significantly over the frequency range (and it probably does, although as I mentioned I couldn’t find an impedance curve for it), the interaction of that relatively high amplifier output impedance with the speaker’s impedance variations is likely to have unpredictable tonal consequences that were not intended by the designer.

To minimize that you would want to choose a tube amp having relatively low output impedance, which correspondingly means a damping factor which is relatively high (for a tube amp). I would certainly not feel comfortable choosing an amp having a damping factor of less than say 8, and many and probably most tube amps do not meet that requirement.

Makers of tube amps having relatively low output impedance/high damping factors include Audio Research, Music Reference, McIntosh, and possibly various VAC models which provide a 2 ohm output tap. However finding an amp which provides adequate power, low output impedance/relatively high damping factor, high quality sonics, and meets your stated budget, is likely to be a challenge. Personally I would follow the advice of those who recommended staying with solid state.

Regards,

-- Al

@bestbaker  You might want to read this thread- it deals with exactly the same issues you are dealing with.
https://forum.audiogon.com/discussions/recommendation-for-higher-power-tube-ampIn a nutshell since your speakers are 4 ohms the efficiency is 3dB less than the stated 87dB.


Efficiency is a much more useful spec when dealing with tube amplifiers as tube amps don't double power as impedance is halved.


The bottom line is if you want satisfying sound pressure *and* you want tubes, you are far better off getting a speaker that is not so inefficient!

Sanders biases his arguments towards his own amps which are admittedly great values in high powered amps. Yes, high powered tube amps waste a lot more energy as heat than an AB SS amp. He is also expressing his opinion with a bias toward driving his electrostatic speakers. He dismisses OTL amps off hand. He is right that you need to use a lot of tubes to reduce the impedance of the output section but once you do so they are every bit as effective at driving electrostats as SS amps.

@mijostyn
ESLs don't obey the same rules of loudspeaker operation as conventional box speakers; no doubt because a box isn't involved for starters :)  As a result, to make them more compatible with solid state (as otherwise ESLs are *far* more compatible with tubes), Sanders made his speakers fairly low impedance, just like Martin Logan. This results in impedances that are south of 1 ohm at the upper range of the speaker. For more on how this works seehttp://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

In a nutshell since your speakers are 4 ohms the efficiency is 3dB less than the stated 87dB.

Hi Ralph (Atmasphere),

In this particular case the 87 db spec is stated to be based on an input of 1 watt, rather than on an input of 2.83 volts. Also, as I mentioned in my previous post the brochure for the speaker states that an input of 8 watts results in an SPL of 96 db at 1 meter, which is consistent with 87 db/1 watt/1 meter. So if those numbers are accurate the efficiency is 87 db, rather than 84 db.  

Best regards,

-- Al

VTL 300 Deluxe would work if you want tubes. Personally my AR-90s never really sounded that good with tubes. What you need is high current SS. I like Threshold myself. Using a 550E at the moment but my 300 worked well. I'd love a pair of SA/1 but need the coin.