Pass Labs xa - .5 amps

06-04-09: Rtn1
With all due respect, I do not understand why one would use efficient, tube-friendly speakers and then use a solid state amp.

Rtn1, are you referring to me? If so, I have used tube amps with the Sonata III with unsatisfactory results.

The Sonata III have an impedance curve that dips below 5 ohms. They are not as tube friendly as the sensitivity and nominal impedance suggests. Extensive discussions with Ralph Karsten of Atma-Sphere corroborate this conclusion.

As I mentioned, Alan Yun voices his Silverline speakers with Pass Labs amps. There must be a good reason.

I have used tube amps with the Sonata III with unsatisfactory results.
Tvad (Threads | Answers)

To be more exact, the result was a tonal imbalance with the highs louder than the bass and midbass, resulting in a tipped up or bright sound. The tube amps used were VAC MusicBloc 160 push pull and Atma-Sphere M-60 OTL.

The XA-60.5 amps produce tonally balanced sound, and the tipped up characteristic is gone.

>>Solid state should be for inefficient speakers (4 ohm and less, 90db and below) that have a different set of sonic priorities.Rtn1<<

Totally disagree.

Rabbani, your choice of speakers will depend on your room size. I'd suggest anything 90+ dB given a small or medium size room. A large room would require a more sensitive speaker.

Impedance curve characteristics are of less importance since the XA-.5 series amps double power as speaker impedance is halved.

However, IMO, you should choose speakers before selecting an amp. Having done it the other way around, I realize what a mistake it is.

To be more exact, the result was a tonal imbalance with the highs louder than the bass and midbass, resulting in a tipped up or bright sound. The tube amps used were VAC MusicBloc 160 push pull and Atma-Sphere M-60 OTL.

Physically that might be explained by the higher output impedance of the tube amps. As output impedance nears that of the speaker then you will modulate the amount of voltage reaching the voice coil by the variation of the speaker impedance with frequency. For example, if the amp has an output impedance of 4 ohms then where the impedance of the speaker drops to 4 ohms you will get roughly half the voltage at the voice coil than you get at a point where the speaker impedance rises to 40 ohms (at 4 ohms half the voltage is dropped across the output of the amp while at 40 ohms only 10% is dropped). Obviously, if the speaker has been designed to be flat in frequency response when driven by an SS amp then you will hear a "tilted" presentation when played with a higher output impedance tube amp.

I am sure Tvad knows this very well - having directly experienced it and based on all his other knowledgeable posts here on Audiogon. So my comments are simply intended for those who are puzzled as to the cause of Tvad's observations...that's all.