Tube Amp Questions

My suspicion is that the VS110, as well as many other tube amps, would be a poor match for the Thiel CS3.7. From Stereophile’s measurements of the speaker:

...the CS3.7’s impedance remains between 2 and 3 ohms over much of the audioband (fig.1), and that there is a demanding combination of 3.8 ohms and –40° capacitive phase angle at 60Hz. Thiel specifies the impedance being nominally 4 ohms, with a minimum of 2.8 ohms. I actually found the minimum impedance to be 2.4 ohms at 125Hz. The difference between 2.8 and 2.4 ohms is academic, either mandating use of an amplifier that has no problem delivering high currents.

Figure 1 at that link, which depicts the speaker’s impedance magnitude and phase graphically, further reinforces my belief that the CS3.7 is not a tube-friendly speaker.

Also, as stated in Stereophile’s measurements of the VS110:

The output impedance from the 4 ohm tap was a fairly high 0.72 ohm across most of the audioband, this rising to 1.3 ohms at 20kHz. The equivalent figures from the 8 ohm tap were 0.93 ohm and 1.9 ohms, respectively. As a result, the modification of the amplifier’s frequency response due to the Ohm’s Law interaction between its output impedance and the way in which a speaker’s impedance changes with frequency will be quite large.

So IMO, generally speaking, a solid state amp would stand a much greater chance of being an optimal match for that speaker. Although in choosing one keep in mind that its input impedance should conform to ARC's load recommendation for the LS7:

Recommended load 60K ohms and 100pF (20K ohms minimum and 1000pF maximum)

(The pF part won’t usually be a problem, unless the interconnect cables are unusually long. But many and probably most solid state amps will have input impedances below 60K ohms, although I wouldn’t worry about it if the input impedance is around 30K or more).

It may be worthwhile for you to search Audiogon’s "Virtual Systems" section to see what amplifiers others are using with the CS3.7 or similar Thiel speakers.

Good luck. Regards,
-- Al

almarg +1. Thiels love SS amps. The tube pre is O.K.
Speaking as a former Thiel owner (1.6 an 2.4SE).
150 wpc minimum.

I would suggest a Pass X..5 or .8  series amplifier size would depend on budget. Thiels like current and need to be feed properly to sound their best. 

Chuck 

Just FYI. I am using a Belles Reference 150a V2 amp with really really good results with my Thiel 2.4's. So if your budget is like mine this my be a very good amp for your 3.7's. Some people think that it's sound doesn't suggest a strong association with solid state, but sounds somewhere between tubes and solid state in a good way.

What about class D amps?