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I won't pretend for a moment that reproducing disc warps is a good thing; it increases LF distortion from the speakers and wastes amplifier power that is better directed toward reproducing program material. But the place to control that garbage is in the cartridge/tonearm, through the choice of a sensible, well-damped LF system resonance, and in the preamp phono stage, by adherence to the IEC/RIAA's standard playback flatten-out below 50Hz. Even the subsonic filters found in some preamps tend to thin out the low end. If the arm/cartridge LF resonance is effectively damped, so the peak is of…
Martin Colloms closes
Until recently, the largest Audio Research power amplifier was the D-250, a massive, fan-cooled stereo chassis offering 250Wpc into a well-matched load. With its 16 output tubes, plus many others besides, designing and manufacturing the D250 represented an act of considerable courage on the part of ARC! Now in Mk.II form, the D-250 stands as one of the great high-power amplifiers.
Traditionally, ARC power amplifiers were stereo units, but the virtues of monoblock operation were also explored in a version of the D115 called the M100. Ultimately this proved to…
Speaker connections are made on the M300 rear panel via the terminal panel, ideally requiring good spade terminations to the speaker cables. A center tap connector is provided and acts as a "low" terminal in unbalanced mode, but otherwise is not used. Three pairs of terminals provide for 2, 4, and 8 ohm matching. Audio input is via a gold-plated Tiffany RCA socket with an input impedance of 60k ohms, and a gain control is permanently wired in circuit.
Design and Technology: How has the output power been raised to 300W with the established configuration of eight push-pull 6550 output…
Before further complicating the issue, let me state right away that the M300 is a very fine amplifier, and one which I greatly enjoyed assessing. It provides a huge dynamic range with low background noise despite the high sensitivity, together with a genuinely high maximum program capacity of over 300W. Large-scale orchestral works were reproduced effortlessly, while its power reserve on rock program was such that one's aural tolerance fails long before the amplifier reaches its limits.
However, my first reaction to the M300 was one of disappointment, having set it up on the 8 ohm…
This brings me to the final point of the subjective analysis: stereo focus. Very good, rather than exceptional, results were obtained here, and, compared with other noted monoblocks, the specific images of individual instruments were a little broader and vaguer, something you might not notice except with a better amplifier driven by reference-quality source equipment (eg, a Goldmund Reference!).
On the 4 ohm setting the M300 spoke with undisguised authority, breathing an articulate, lively dynamic quality into the reproduction of recorded music and providing abundant depth where the…
Sidebar 1: Specifications
Description: Hybrid mono power amplifier. Rated power: 300W, 16Hz-20kHz into 2, 4, or 8 ohms, at below 0.8% THD. Power bandwidth: 10Hz-60kHz. THD: 0.05% at 1W output. Clipping: 330W at 1kHz, nominal. Input impedance: 60k ohms. Feedback: 20dB. Slew rate: 25V/us. Rise time: 3us. Sensitivity: 0.9V in for 300W out. Damping factor: About 30. Hum & noise: Less than 2mV RMS; 90dB below full output. Power consumption: 130W on standby, 450W quiescent (no signal), 900W at rated output power.
Dimensions: 19" W by 10½" H by 16" D. Weight: 110 lbs.
Price: $9800/…
Sidebar 2: Measurements
While many lab tests were easily passed, the M300 did exhibit some odd quirks which suggested that there is still room for further development and improvement in future years.
8 ohm tap: Covering the basics first, the power testing commenced (after two hours' warm-up) with 8 ohm loads on the 8 ohm tap. Rated at a continuous 300W or 24.5dBW, this amplifier raised an extra 1dB heading toward an exact power of 400W into the precise load impedance (7.7 ohms)—some power indeed! In terms of a marginal clipping criterion, the power bandwidth was excellent,…
Manufacturer's Comment
Editor: Thanks for the opportunity for us to comment on the early draft of Martin and Gordon's M300 review. We were unable to reach you by phone, so here are a few comments on technical errors.
First, we are naturally pleased and grateful for your thorough and complimentary review, as well as your suggestions for improvement.
1. Our published THD rating at 1W midband is 0.005%, not 0.05%.
2. The 2.2% THD at 20kHz, 1W, is much higher than typical. This is probably due to an unbalanced capacitive load from a single-ended input on a 'scope or…
J. Gordon Holt wrote a Follow-up on the Audio Research M-300 in January 1988 (Vol.11 No.1):
Some additional listening to a pair of these big amplifiers, which I reviewed in Vol.10 No.9, revealed that they do have one relatively minor weakness: their low end is not quite as detailed or tightly controlled as that of some big solid-state amps (like the Krells and Thresholds). Otherwise, their sound continued to enchant me until...I had turned the volume down while changing a record, and when I next touched the knob, a static discharge produced a very small click through the speakers,…
I told a friend that I'd received a pair of Vienna Acoustics' new Beethoven Concert Grand loudspeakers for review. "They're designed more for music lovers than for audiophiles," he said. I can't imagine a more damning statement—about audiophiles.
"What are you saying?" I sputtered. "That being an audiophile and being a music lover are mutually exclusive? How can a speaker designed for someone who loves music not be a speaker designed for an audiophile?"
His cryptic reply: "Let me know what you think after you listen."
Until the Beethoven Concert Grands arrived in…