No disrespect to Ralph, but I think there are significant drawbacks to OTL designs, including Atmasphere. I've owned the latest M60 with all the factory upgrades except for the volume control option. First, speaker choices are limited to those that are 8 ohms or higher, which have been pointed out. Using an Speltz autoformer for speaker/amp impedance matching is defeating the purpose of OTL. Might as well get a transformer coupled tube amp and be done, which will give you much wider range of speaker options. I've found the tube noise in M60 to be unacceptable, especially if you have high efficiency speakers. I've had several output tube failures within first 6 months of ownership. Granted this is just my amp, but I've heard from other Atmasphere owners who have had this problem. When the output tube fails, it is quite alarming because you get a loud pop. It did not damage my speaker though.
The plus side to the sound of the Atmasphere M60 is crystalline high frequency (probably the best I've heard) and ultrasmooth midrange. The soundstage is huge, but the image specificity is more diffuse than other tube and solid stage amps. Bass can be loose, if you don't have the proper impedance matching. I think Atmasphere are more true to life than any SET amp I've heard. SET amps have their magic emotionally involving sound, but I don't think they are like live music unless you limit your music to simple vocals, simple jazz ensemble, chamber music and the like. It's hard, if not impossible, to get life like macrodynamics using a SET amp unless you have 100 dB+ horn speakers, which are IMO colored transducers, although horn fans are likely to disagree.
IMHO, good high power PP tube amps sound more like the real thing and work well with almost any speaker out there, including ribbon and electrostatic speakers.
The plus side to the sound of the Atmasphere M60 is crystalline high frequency (probably the best I've heard) and ultrasmooth midrange. The soundstage is huge, but the image specificity is more diffuse than other tube and solid stage amps. Bass can be loose, if you don't have the proper impedance matching. I think Atmasphere are more true to life than any SET amp I've heard. SET amps have their magic emotionally involving sound, but I don't think they are like live music unless you limit your music to simple vocals, simple jazz ensemble, chamber music and the like. It's hard, if not impossible, to get life like macrodynamics using a SET amp unless you have 100 dB+ horn speakers, which are IMO colored transducers, although horn fans are likely to disagree.
IMHO, good high power PP tube amps sound more like the real thing and work well with almost any speaker out there, including ribbon and electrostatic speakers.
