To Doug Schneider,
I just read your response to a reader. I have the Leben CS600 and Vienna Acoustics Mozart Grand speakers. At low and medium volume, they are magical. However, when I turn up the volume to "room filling" levels, the treble becomes harsh and brittle sounding. I've tried different tubes and various positions but nothing works. At this point, I'm ready to sell and try something different.
I’m not surprised that the amp works well at low and medium volume levels, because it doesn’t take that much power to get half-decent output from a speaker. To go louder, though, you might need quite a bit more power, since each 3dB SPL increase from the speaker requires a doubling of amplifier power. That harsh and brittle sound you’re hearing is likely nothing more than the amp running out of power and distorting. . . . Doug Schneider