May 9th, 2009 -- by Guido Corona
Source: The Absolute Sound
Comfortable with the warm heft of my 20-year old JRDG Model 7M monoblocks, and somewhat familiar with the clean but admittedly polite sound of the original Jeff Rowland 302, I was totally unprepared to fall in love with the robust yet agile grace of Rowlands newest stereo amplifier flagshipthe 312. Authoritative rather than merely precise, harmonically textured rather than simply detailed, filigreed in the treble rather than merely extended, the 312 controlled my Vienna Mahlers like an iron fist in a velvet glove.
Weighing a hefty 83 pounds, the 312 is hardly a minimalist device. According to Jeff Rowland, it combines the third-generation ASP 1000 ICEpower conversion modules at its core with custom-engineered input and output circuits, as fundamental building blocks of a sophisticated instrument-grade amplifier. While the original 302 exploited second-generation ICE modules capable of a respectable 360W into 8 ohms, the twin third-generation ASP 1000 modules of the 312 deliver 500W into 8 ohms and 1000W into 4 ohms.
Yet, JRDG has shaved almost 20 pounds off the 312 by adopting a new dual mono design. The single massive transformer and custom switching power supplies of the 302 have been replaced by twin 700W PFC units feeding much lighter dual power transformers that control switching power supplies integrated into the ICEpower modules. The internal operating voltage in the output stages has been raised from 84V to 125V DC, and furnishes a peak current of 45A of balanced power to the 312s patented Cardas output binding posts. New circuitry prevents damage to the amplifier caused by occasional shorting of speaker wires.
According to JRDG, Power Factor Correction (PFC) is the key to the 312s musicality. PFC taps energy out of an inductor circuit during the entire AC cycle100,000 times per second through a high-speed switch. By using energy out of the wall outlet to charge the 312s power-supply capacitors during most of the AC cycle, it lets the 312 achieve an astonishing power conversion efficiency of almost 98%. PFC also minimizes distortions caused by 120Hz peak surge currents during capacitor charge, and subsequent deleterious back pulses into the AC mains grid.
Jeff Rowland suggests that break-in of ICEpower modules, input transformers, and other electronic components may take a particularly long time. Even after several months, some residual magnetization and electric fields may slowly build up during long overnight idle time, only to ebb gradually once more to a vanishing point during playback. Thus, while the 312 may be kept always operational thanks to its extreme efficiency, audible parameters like its impressive bass control and musicality, its delicate texturing of harmonics and treble, and its remarkably effortless authority are not necessarily realized instantaneously after a full night of idling; yet, in just a couple of hours of playing music, they gradually blossom once more into characteristic magnificence.
http://www.avguide.com/review/first-look-jeff-rowland-design-312-power-amplifier