Audio Research M300 monoblock power amplifier Page 6
However, my first reaction to the M300 was one of disappointment, having set it up on the 8 ohm winding with straightforward 8 ohm speakers. The sound was certainly good, but in context appeared rather forward in the mid register, with a mildly dulled extreme treble, and less clarity and depth than was hoped for. In some respects the detail resolution in the mid register was poorer than three of the amplifiers used for comparison, while the main treble range could have been more liquid.
In addition, the stereo focus was unexceptional, and not really to the standard expected of a monoblock design of this caliber. Stage width was slightly narrowed, though the amplifier did hint at a potential for good depth.
Experience with the M100 was recalled where experiments with the impedance taps proved worthwhile; indeed, with the M100 I invariably used the 4 ohm match except on occasions when that last 3dB of full power was deemed essential. In fact, the last ounce of system performance was wrung out of the M100 by bi-wiring the loudspeakers where possible and taking the treble section to one 4 ohm winding and the bass section to the other. (Take care to respect phase when making this connection, and note also that the "two" 4 ohm windings are 16-4 and 4-0, with 4 as the common zero balance terminal. This recommendation applies to previous ARC power amps with 0-4-8-16 ohms transformers.)
The M100 and D115 had 4 ohm taps which were not fully balanced; those for the M300 are balanced, and the 4 ohm terminals were tried forthwith.
It is probably an exaggeration to say that the results on 4 ohms were revelatory, but that is precisely what my notes taken at the time suggest. Given the huge available power, the loss in level on the 4 ohm tap passed unnoticed (a loss of 3dB in absolute peak level for 8 ohm speakers). In return, we were provided with the sound we had anticipated from a new flagship ARC product. Immediately, the midrange forwardness was seen to be largely corrected, along with the related congestion and compressive effects. In the treble, better definition and clarity were observed, while the bass was noticeably faster and more articulate. Focus improved to very good, falling just short of a potential "excellent," while the stereo width remained slightly narrowed, both on front and rear stages.
This general improvement helped to produce a dramatic change in transparency and stereo depth, which were both unreservedly described as excellent. Here the M300 was a star performer, rivaling the Jadis JA200 in this area, while providing more control and definition out to the frequency extremes of low bass and high treble. The large scale and power of the M300 reproduction, coupled with its superb depth and ambience, created a highly realistic and believable soundstage, albeit slightly narrowed.
On the 4 ohm setting the bass was very good indeed; I am inclined to believe that, qualitatively, it was one of the very best, if still slightly dry. Highly articulate and natural, bass sounds were allowed to thrum and sing in a most natural manner, while conceding very little in terms of sheer speed and slam.
Over the broad midrange, the M300 clearly spoke with a highly neutral voice—low coloration was the theme here, while the level of individual detailing and instrumental articulation was also of the highest order. There remained a hint of coarseness and grain, though rather less than most.
It was also very good in the treble. I did eventually decide that while it did not spoil the brew, the M300's performance in this area was not its best point. A mild roughening and grain was just audible, a little less than natural-sounding, and slightly forward of and detached from the midband format image focus. Nonetheless, the treble was highly detailed, and, as noted in this 4 ohm condition, showed fine extension with the correct degree of air and sparkle.