Going Tubing

A tube amp with an output impedance of 1 ohm and greater will have the most effect as the tube amp will track the speaker impedance and will not have a flat response (Ohm's Law). It will act like a tone control. So "colored" sound is the result.

I generally agree with both responses so far. Only thing to counter Jason’s comment is that while his statement is generally accurate, I would say that coloration depends on the design of the tube preamp or amp. I have heard very colored tube preamp (e.g. Cary SLP-05) and not so colored tube amps (e.g. Audio Research REF 150 SE), but in most cases, a true tube amp likely would add more coloration that most tube preamps.

Depending on the speaker’s impedance curves and sensitivity, one may prefer to match them with tube or solid state. Many opt for a tube preamp with a solid state amp because it can deliver a harmonic presentation while confidently controlling a wider variety of speakers. If the speakers are hard to drive, the requirements of a tube amplifier tends to go up exponentially, as does the price. 

Thanks for these responses!

My speakers are GoldenEar One.R:s. Sensitivity is pretty solid at 92 dB, and they have built-in subs so I would assume a need to push a great deal of power to them wouldn’t be necessary. Thus a - typically - lower power tube amp (compared to ss amps) may be sufficient, and not too much a concern/consideration.

Starting off with a tube preamp seems to make sense, though. I am eying the Black Ice Fusion F360, not least because of its rather intriguing sound field “enhancing” feature, designed by Jim Fosgate.

Here is an excerpt from John Atkinson’s Measurements section for your speakers…

“The One.R’s impedance is specified as being "compatible with 8 ohms." The solid trace in fig.1 reveals that the impedance magnitude ranges between 3 and 6 ohms for much of the audioband, with a minimum value of 3.1 ohms between 290Hz and 390Hz. Like the original One, the One.R’s use of a passive high-pass filter with a low corner frequency means that the electrical phase angle becomes increasingly capacitive below that frequency. Although the impedance magnitude rapidly increases below 100Hz, mitigating the effect of that phase angle, there is still a combination of 4 ohms and –48° at 100Hz, which will require a good 4 ohm–rated amplifier to drive the speaker to acceptably high levels.”

This doesn’t scream tube friendly to me and almost certainly not for a lower-powered tube amp as it will easily be forced into operating out of its comfort zone. Makes a lotta sense to just start with a tube preamp and then decide if you wanna spend $$$ on a higher powered tube amp. Hope this helps, and best of luck.