UID321216
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金钱1546
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注册时间2006-10-10
最后登录2013-3-6
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注册时间2006-10-10
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发表于 2013-2-28 17:46
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Conrad-Johnson is one of audio's "marquee" companies, and charges accordingly. The Premier Twelve tube monoblock power amplifier, rated at 140W, sells for a rather steep $3495 each, meaning that unless you listen in mono, be prepared to lay out almost $7000 just for the amplification link in your audio chain. Apparently, many audiophiles feel the money is well spent: according to Conrad-Johnson, the Twelve has been a consistently strong seller during its approximately five-year production history. What do you get for your $7000, aside from 140Wpc and a top-shelf name? Physically, you get a pair of graceful, low-slung amplifiers that combine open architecture with a removable protective tube cage. Cosmetically, you get the clean, brushed-brass-and-black C-J "look." The circuitry is relatively straightforward: a triode amplifier input stage using two halves of a 5751 twin-triode tube in parallel, direct-coupled to a pair of cathode-coupled phase splitters (6FQ7s) outputting a balanced, low-impedance signal to two pairs of push-pull 6550s (new old stock GEs). The output tubes are coupled to a large output transformer (custom-engineered and built to Conrad-Johnson's specs) said to feature high phase linearity and wide bandwidth. A 12dB negative-feedback loop is used to lower distortion and raise the damping factor so the amplifier can better handle reactive loads. In other words, nothing too exotic or retro is going on. The key to the Premier Twelve's success must be more in the execution than in the design. The power supply includes separate DC regulation for the input and phase-inverter stages (which C-J claims prevents them from being "back-modulated" by the output stage), and four large, custom-made polypropylene capacitors (in parallel with polystyrene) in place of the usual electrolytics. Parts quality on the two boards—one for the power supply, the other for the audio—is high, including Vishay resistors and custom-made polystyrene capacitors in the audio circuit. There are no electrolytic capacitors in the audio circuit or its related power supplies.
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