I've heard most of the 845 amps on the market since the mid-90s. The very best I've heard are the Audion Black Shadow SET monoblocks. The Audion Elite is the same circuit in a three-chassis configuration that isolates the power supply to a third chassis. I ended up buying them, now seven years in. I haven't yet heard an 845 amp at any price that can equal or exceed their sound quality.
The Audion 845 amps benefit from a simple circuit: solid state rectification, one input tube, one driver tube and the 845 power tube. Internal components are premium quality, the audio wirepath is silver, transformers are Audion's own and are excellent. The only way in which I've heard another 845 amp better the Black Shadow is in noise. The Audion amps are not noisy in context of everything SET, but the also-excellent Sophia 845 is quieter -- probably the quietest 845SET amp I've heard. The Sophia amp is also the closest to the Audion in total sound quality. Now, keep in mind that the noise in the Black Shadows is only noticeable when music *isn't* playing. And if you listen to vinyl, source noise will completely overwhelm the amp noise in even the quietest of passages. But if you're open to SET, you're signing up for more noise than conventional push-pull tube or solid state gear anyway. Further, there are options for reducing the nominal noise of an Audion 845 amp to, by comparison, Sophia levels.
Why the Audion amps? They have the character of live, unamplified music: able to combine exceptional revelation of nuance with visceral dynamic punch. They have the tone density of flea power SET amp without their slowness and sunset glow. The Black Shadow, like all Audion amps, is uniquely "fast" and absent the dulling or rounding of transient events yet also completely absent any emphasis of the leading edge that comes with so many solid state or modern tube amps voiced to sound like solid state.
Spatial presentation is sacrificed to power, as often happens with gutsy push-pull amps. The unity of presentation and the amp's ability to keep simultaneous events and tones sorted is really remarkable, especially under crescendo conditions. Some other otherwise very good 845 amps blur complexity in music when power requirements surge. Not the Audions. Presentation stays intact throughout their dynamic range. The transparency into the character and truth of a recording is obvious but also so normal that you scarcely notice it until you take it away by substituting another amp. You get all this without damage to the basic hifi necessities of truthful octave-to-octave frequency balance and evenly distributed dynamic range. Voice tells the tale. You won't want any other 845, if you can afford these.
All that said, 845 amps in general are an excellent category to choose from, and price plays its role. But if sound quality alone drives you, I put Audion at the pinnacle of the pyramid, with Sophia a close next-best. Several Chinese makers are coming on strong. On any of these amps, the choice of 845 tube has a big effect on overall character. Most ship with the cheap and cheerful Sino 845A. It's fine but sounds a little chalky, white. It also gives all these amps less spatial realism than almost every amp is capable of. The 845B seriously improves things. Some people go further and recommend the Psvane 845T, which I haven't heard.
A polar graph of attributes would show the Audion to have the closest to a perfect circle of fidelity, Sophia close behind. Everything else gives up something, but can still sound sensational. These two front runners yield vivid yet delicate, punchy yet nuanced, toneful yet ascetic presentations as the music calls for, and bass will be among best you'll hear from a tube amp of any topology. There are push-pull 845 amps as well, but they won't match what these SET amps can do, albeit with less power.
Phil
The Audion 845 amps benefit from a simple circuit: solid state rectification, one input tube, one driver tube and the 845 power tube. Internal components are premium quality, the audio wirepath is silver, transformers are Audion's own and are excellent. The only way in which I've heard another 845 amp better the Black Shadow is in noise. The Audion amps are not noisy in context of everything SET, but the also-excellent Sophia 845 is quieter -- probably the quietest 845SET amp I've heard. The Sophia amp is also the closest to the Audion in total sound quality. Now, keep in mind that the noise in the Black Shadows is only noticeable when music *isn't* playing. And if you listen to vinyl, source noise will completely overwhelm the amp noise in even the quietest of passages. But if you're open to SET, you're signing up for more noise than conventional push-pull tube or solid state gear anyway. Further, there are options for reducing the nominal noise of an Audion 845 amp to, by comparison, Sophia levels.
Why the Audion amps? They have the character of live, unamplified music: able to combine exceptional revelation of nuance with visceral dynamic punch. They have the tone density of flea power SET amp without their slowness and sunset glow. The Black Shadow, like all Audion amps, is uniquely "fast" and absent the dulling or rounding of transient events yet also completely absent any emphasis of the leading edge that comes with so many solid state or modern tube amps voiced to sound like solid state.
Spatial presentation is sacrificed to power, as often happens with gutsy push-pull amps. The unity of presentation and the amp's ability to keep simultaneous events and tones sorted is really remarkable, especially under crescendo conditions. Some other otherwise very good 845 amps blur complexity in music when power requirements surge. Not the Audions. Presentation stays intact throughout their dynamic range. The transparency into the character and truth of a recording is obvious but also so normal that you scarcely notice it until you take it away by substituting another amp. You get all this without damage to the basic hifi necessities of truthful octave-to-octave frequency balance and evenly distributed dynamic range. Voice tells the tale. You won't want any other 845, if you can afford these.
All that said, 845 amps in general are an excellent category to choose from, and price plays its role. But if sound quality alone drives you, I put Audion at the pinnacle of the pyramid, with Sophia a close next-best. Several Chinese makers are coming on strong. On any of these amps, the choice of 845 tube has a big effect on overall character. Most ship with the cheap and cheerful Sino 845A. It's fine but sounds a little chalky, white. It also gives all these amps less spatial realism than almost every amp is capable of. The 845B seriously improves things. Some people go further and recommend the Psvane 845T, which I haven't heard.
A polar graph of attributes would show the Audion to have the closest to a perfect circle of fidelity, Sophia close behind. Everything else gives up something, but can still sound sensational. These two front runners yield vivid yet delicate, punchy yet nuanced, toneful yet ascetic presentations as the music calls for, and bass will be among best you'll hear from a tube amp of any topology. There are push-pull 845 amps as well, but they won't match what these SET amps can do, albeit with less power.
Phil