An Amplifier Change for my Wilson Sophia 2's?

The signal response measurements are done at 1kHz.

Most ARC amps have lower effective output impedances than the majority of tube amps, and the VT100 is no exception to that. Specifically, it has a specified damping factor of 11, which for the 4 ohm tap corresponds to an output impedance of approximately 4/11 = 0.36 ohms. Per JA’s measurements the minimum impedance at any frequency of the earlier version of the Sophia is 3.26 ohms, with a near-zero phase angle (i.e., an impedance that is almost purely resistive) at that frequency. And at nearly all other frequencies the impedance is significantly higher.

As you’ll probably realize, the result of the interaction of that kind of amplifier output impedance with those speaker impedance characteristics will be not much different than would occur with a solid-state amplifier, namely very little variation of output voltage as a function of frequency. And yes, in a narrow range of frequencies in the area of about 40 to 50 Hz, where the speaker’s impedance rises to around 14 ohms (assuming the speaker’s impedance characteristics are similar to those of the earlier version of the Sophia), and also in the upper treble region where the impedance also rises significantly, the amplifier’s power capability will therefore probably be significantly less than at 1 kHz. As a result of limitations that presumably would occur in output voltage, however, not as a result of limitations in output current as you had stated.

However in the rest of the deep bass region, as well as in the mid-bass and mid-range regions, which encompasses the regions where most music contains most of its energy, the 1 kHz power capability measurements can be expected to be essentially applicable.

Regards,
-- Al

Wilsons are pretty efficient and you have a fair amount of power. I agree with those who suggest that you may need more gain in your phono or line level preamps. I have heard many Wilsons from Sophia to Alexandria XLF, and they always sounded great with tubes, esp. ARC and VTL. 

I have run Sophia 2's with 30W OTL's (Berning)  60 W OTL's (Atma's)
and class A and AB SS from 40W to 200W and always had plenty of volume. Yes, some differences in sound, but never anything unpleasant.
They are fine floor standing speakers and do well with just about any power.  I guess something may be off in your source or pre amp to amp match.
Or maybe you are chasing high sound volumes that really rock.  In that case my best suggestion is the old original KlipschHorns, and be sure to stick them in the corners of the room.  But do not do that to Sophia's.
Good luck.

Would it make sense to replace the tubes, assuming that the ones installed are no longer capable of peak performance? Just a thought. 100 tube watts should be enough for these speakers.

So clearly there are a lot of viewpoints on this subject!  That is to be expected as I am learning that speaker - amplifier matching seems to be one of the black arts.  Thank you all for your posts.

To sum up, some say speakers need loads of wattage to get control, tight bass, and better imaging.  some say even hungry speakers do fine with lower wattage tube amps.

I spoke to Wilson Audio and their man that I spoke to said that the speakers do indeed react well to lots of wattage.

There are two issues I am raising here.  One, I feel I am raising my volume control too high to get where I want to be, and this is a gain issue.  The 2nd is the question of wattage and control, and what to feed my Sophia 2's so they deliver their best work.

One suggestion was the preamp (phono or one stage) was not giving enough gain.  If I followed that route and get a preamp that has more gain, such as the ARC LS26 with 24db of gain, compared to 18db of gain in my LS-25, that would solve only one of the issues, and I would not know if the extra power amp wattage will be adding a lot of improvement with the Wilsons.  (side note, I checked the specs on all of the ARC REF line stages from the Ref 1 to the Ref 10, and all have super low gain.  Much less than my LS-25!  If I were to pony up for a Ref 3 at some point, I don't think I would have enough gain to drive the speakers to the volume I like at all!  Seems odd to me.  Perhaps if one wants a Ref series line stage, one needs a particularly high gain amplifier, but I digress).

For my budget ($2200), I am leaning towards the Bryston 4BSST at the moment.  23db or 29db of gain (selectable), 500 watts in 4 Ohms, this has the right price point, solid warranty, 6db increase in gain, and 5 times the wattage.  (Al, it also has 20K load impedance that you warned about for matching to the LS-25.)

Today I am going to read up on how amplifiers work, so I can better appreciate Al's comments, which are a bit over my head!  Time to study.