Most transparent power amp

@fsonicsmith, I think you are addressing me, not George since the quote is mine.

The DeVore is not a four ohm speaker; as far as their website is concerned, they don't make any. But it works best on your four-ohm taps. That is quite a bit different from the speaker actually being four ohms. It simply means that combination works best for you- and as you noticed, the speaker cable is a bit critical in the overall scheme of things.

Can you unequivocally state that using the 4 ohm taps on any tube amp, including my ARC Ref150se, ipso facto results in brightness and hardness?

Not- at all, and if you got the impression I said that, I didn't. What I did say is that the use of four ohm speakers results in higher distortion from any amp- and that the distortion is such that is perceived as brightness and hardness. There is a distinction here- you are not using a 4 ohm speaker.

Using the four ohm tap gives you the lowest output impedance available from the amp and for some reason that works. FWIW, usually you loose some bandwidth using the 4 ohm tap; IME its usually in the bottom octave.

Yes, Ralph, sorry. 
Thx-I misread your post. I think I was tired from a long day at the office when I read it. When you said;

The simple fact is that four ohms is not good for **any** amplifier made regardless of the technology, and this is easy to see in the amplifier's specifications.

I thought that "four ohms" referred to the amp side of things and not the speaker. Your post is clear, it was my failure to carefully read it. 

@georgehifi 
There are "passive" amps. The First Watt F4 is an impedance converting amp with exactly 0 dB of gain that only serves the purpose of delivering the current so that a line level signal can be fed to the speakers. 

Kosst, not to belabor a minor point, but a "passive" electronic device would usually be considered to be one having no "active" components (e.g., transistors or tubes), at least in its signal path. A device which provides zero voltage gain but amplifies current and power is not a passive amplifier, in the sense that George was using the term and per what seems to be generally accepted terminology.

Regards,
-- Al
   

@almarg 
In a strict sense, yes, but passive preamps utilize active components to buffer the input, volume, or both, so that the variation in impedance by the volume control doesn't reshape the response. Generally, so long as the circuit's goal is impedance conversion, it's called passive because it's doing the job of a passive component, namely a transformer.