Tube amplifier to power Sonus Faber speakers?

Georgelofi gives spot on advice and the poster is strongly advised to follow it. You will need a good SS amp for these speakers. Another idea is a good hybrid amp!

Thanks to George for finding and pointing out the HFNRR review of the speakers, including the measurements. And kudos to Bruce (Bifwynne) for suggesting the very same ARC Ref75 amplifier which the reviewer, Ken Kessler, utilized in evaluating the speaker.

A couple of corrections to some of what has been said earlier in the thread:

First, on a per watt basis the speakers are not even close to being 90 db. They are rated as 90 db/2.83 volts/1 meter, and 4 ohms. 2.83 volts into 4 ohms is 2 watts, so their rating is equivalent to 87 db/1 watt/1 meter. The distinction between 1 watt and 2.83 volts (which is equivalent to 1 watt into 8 ohms), in the case of 4 ohm speakers, is especially significant with respect to tube amps, since their power capability does not increase significantly if at all into low impedances (and may actually decrease).

And furthermore, the measurements cited in the review indicate a slightly lower than specified sensitivity, about 89 db/2.83 volts/1 meter, and indicate that the speaker is best considered to be 3 ohms. That translates to only about 85 db/1 watt/1 meter.

Second, a slight correction to something that was said about the VAC Renaissance 70/70: It is a dual mono stereo amplifier, not a monoblock. VAC did manufacture a very similar 300B-based amp configured as a monoblock, though, designated as the 140, and rated at 130 watts.

Beyond that, I'll add to what has been said, and consistent with the earlier comments by John (Jmcgrogan2) and ZD, that the VAC Renaissance amps are the only 300B-based amps I am aware of that I would expect to be able to adequately drive the OP's speakers, for most listeners with many recordings. I say that based on my own experience with a 70/70 (although used in conjunction with far more efficient speakers), on the number of 300B's they use, on the fact that the design drives the tubes very hard (such that some currently available tubes which are non-compliant with the original Western Electric specs cannot be used in these amps), on their robust and very heavy transformers and overall weight, and on the fact that they provide three rather than two output taps, with the lowest being indicated for use with 1 to 2 ohm speakers (on the 70/70), or with 2 ohm speakers (on the 30/30).

That said, finding a Renaissance amp that is in excellent condition and that does not require a major investment in retubing is another matter altogether.

Regards,
-- Al

Thanks for your clarifications Al. Let me add one too.

Most ARC amps use negative feedback and have "low'ish" output impedances, especially off the nominally denoted 4 ohm taps. Al .. as we have discussed many times before, this means that ARC amps with low'ish output impedances perform somewhat like SS amps -- i.e., like voltage Paradigm amps.

As I recall, the ARC Ref 75 has a robust power supply (520 joules) and low'ish output impedance off the 4 ohm taps (1 ohm off the 8 ohm taps; probably less than that off the 4 ohm taps). Ergo, it might not be a bad amp to consider.

That said, if the SF speakers in question (a) present very low impedance plots and highly negative capacitive phase angles in the bass spectrum, and (b) are not very sensitive, then a safer bet might be a high current SS amp with lots of watts. Or, a bigger ARC tube amp such as the Ref 150.

(P.S. J Atkinson measured the Ref 75's output impedance off the 4 ohm taps to be .75 ohms at 20 Hz and 1K Hz. See: http://www.stereophile.com/content/audio-research-reference-75-power-amplifier-measurements)

Here is the simulated load graph that the Ref75 was tested with (1st link) as you can see compared to the flatness of the FR graph (2nd link)black trace, That this amp is relatively flat but is already dipping at 200hz.
But the simulated load at the 200hz is not that heavy and would be far lighter than the SF EPDR of 1.7ohms in the bass.
So even the mighty Ref75 might not fair too well in the bass with the SF speakers..

http://www.stereophile.com/content/real-life-measurements-page-2

http://www.stereophile.com/content/audio-research-reference-75-power-amplifier-measurements

Cheers George

Here's my suggestion and for a LOT less money than the ARC Ref 75....
see if you can source an ARC D70 Mk1, or better still, a Mk2. With my SF's, the D70 Mk2 makes beautiful music. If you think you may need more power ( which I would doubt), then look at a D115 or better a pair of M100's. These older W Z Johnson designs are still IMHO very competitive with some of the best tube gear around. Plus, with the older designs, one isn't stuck with having to run a balanced only preamp up-line.