Muse Model One Hundred power amplifier
I knew it! It was in an issue of Home & Studio Recording, but I'd just thrown it out with a bunch of other old magazines. And trash pickup was today! I threw open the door to watch the garbage truck blunder down the street, my trashcan lid still rolling across the front lawn. As luck would have it, I was wearing my Nike hightops; "Just do it," they seemed to sing like the sirens who had lured so many brave sailors to their watery graves. But my name's not Popeye.
I sprinted down the street after the truck, shouting, "Stop! Please! Stop!" The driver saw me in his rearview mirror and slowed down. Just as I reached the back of the truck, he gave it the gas and the truck lurched forward, the driver's leering face framed in the rearview like some abstract work called Early Hominid in Grey Overalls. Panting like a dog, I chased after him again, and this time when he slowed I sped up, and before he realized what happened I was right alongside the driver's seat, with a head like a caveman's glaring at me from under a dirty maroon baseball cap with the message, "Muscatel: It's Not Just For Breakfast Anymore."
I went back around the garbage truck and peered inside; there was the issue of H&SR I was looking for, nestled comfortably between a pair of size 72 men's underpants and what I will swear on a stack of Radio Shack Electronic Bibles was a human skull with a bit of hair still on it. Holding my nose with one hand, I reached in with the other and slowly extracted my magazine, a little damp and stained but still in one piece. I walked back to the front of the truck to thank the garbage man, but he just grunted something that sounded like "Truckfluidyeti" and drove off.
I got the mag home and there it was, a picture of the Muse's identical twin: Sound Code Systems. And, as I often find out later, the information I just busted my ass for had been right under my nose the whole time, in the letter from Muse's Kevin Halverson. Aw hell, it's not every day you get to meet Piltdown Man.
RH covered the Muse/Sound Code Systems story in his review of the Model One Hundred Fifty, so I won't repeat it in detail here; in short, SCS builds rugged, conventional amps for sound reinforcement and recording studio monitor systems, and Muse builds more refined, high-end amps for the audiophile market. And while the two companies are indeed separate entities, Muse is able to take advantage of their shared lineage (and manufacturing site) in several important ways. For starters, both amp lines use the same chassis, so this part of the design cost for the Muse amps was nil. Also, their combined purchasing power allows Muse to obtain higher-quality components at the same prices most other two-year-old companies pay for run'o'the mill parts. Kevin stresses, though, that while the two amp lines may look alike, their designs reflect their very different markets.
Now wait a minute, I hear you saying; why don't recording studios use audiophile amplifiers? (footnote 1) Shouldn't they use the best, so they can better judge what their mixes sound like? And why don't dogs dance the rhumba with cats?
One word: reliability. For various reasons, most broadcast and recording studio engineers feel that audiophile amplifiers a) break down, and b) don't sound any different from the Crown and Peavey amplifiers most of them swear by. I happen to disagree on both counts. While there have been certain audiophile amps that have had poor reputations for reliability, I would say that this has been an area of great improvement. And quite frankly, I've never heard a pro audio amplifier that I could ever call "musical"; most are rather hard-sounding, with an overly bright high end and glassy mids. Ironically, it's this kind of "golden-ear" nonsensical babble that makes most recording-studio engineers chortle into their copies of Mix magazine (footnote 2). Monitor amplifiers used in pro environments need to be absolutely reliable; failures translate to expensive downtime, resulting in blown sessions and irate producers and performers.
Pro amps tend to be built to a tougher standard than most audiophile units; these amps have to work even after falling out of a moving truck, sitting under water in a flooded facility, or worse. Additionally, most pro amps have elaborate protection circuits that guard against dead shorts in the outputs, overheating, and continuous overload. Unfortunately, most of these circuits degrade the sound, but the pro user is more than willing to make that tradeoff as he doesn't believe in audible differences between amps anyway! I feel that the reliability of many high-end amps is in the same class as the "ol' faithful" pro monitor amps; the Muse Model One Hundred certainly looks as rugged and reliable as any Crown I've seen, and sounds substantially cleaner and less fatiguing.
The Model One Hundred (henceforth called the 100) reviewed here is actually a redesign of Muse's original amplifier of the same name. The engineers at Muse, after extensive listening with electrostatic speakers revealed serious limitations in the older amp, decided that two areas needed improvement: the number of output MOSFETs and the feedback scheme. The results of this rethinking were the Model One Hundred Fifty monoblocks which so impressed RH. After hearing the improvements in the mono 150s, Muse decided to go back and implement these changes in the stereo 100 as well. The number of output MOSFETs was doubled to six per channel (three complementary pairs of Hitachi J50s/K135s), but perhaps even more interesting was the change in feedback topology.
In the original 100, Muse used global negative feedback exclusively. With global feedback, the entire amplifier is treated as a single gain stage, with a portion of the output fed back to the input to cancel distortion and lower output impedance. While it does both well (at least on steady-state signals like sinewaves), global feedback tends to make for a less-stable circuit, especially when driving reactive loads like electrostatic speakers. The alternative to global feedback is local feedback; that is, each individual stage of the circuit is given its own separate negative feedback loop, the result being better sonics and increased stability.
The downside to purely local feedback, however, is a higher output impedance; Muse discovered they could combine the superior sonics of local feedback with the lower output impedance of global feedback by using both. Feedback from three separate points in the circuit is sent to a simple resistive mixer, which allows Muse to vary the ratio of global vs local feedback to achieve the best of both worlds. Muse calls this approach "Mixed-Mode" feedback, and Kevin feels it's largely responsible for the sound of the new 100.
Footnote 1: As in most generalizations, there are always the exceptions: some engineers, like The Mastering Lab's Doug Sax, have used high-end tube amps in their monitor systems for years. It's been my experience, however, that they're far outnumbered by studios equipped with the likes of Crown, Peavey, et al.
Footnote 2: And it's that kind of attitude that makes audiophiles chortle into their copies of Stereophile...round and round and round we go; where we stop is the subject of an AES preprint, "How I Stopped Worrying And Learned To Love The Double-Blind Test."