Audio Research Ref 330M Mono Power Amplifier

The Reference 320M amplifier was originally imagined to be a larger, more powerful version of the Reference 160M amplifier, but it turned out to be a more sophisticated amalgam of designs incorporated in other Reference amplifiers. What was shown in 2022 was a concept, not a product. The 330M is a very different beast, producing 330 watts per channel.

The Reference 330M is unique, combining new thinking, new design, and new parts with the best concepts from other Reference amplifiers. The new front end is a hybrid, using an ECC83 tube rather than a JFET at the input. The ECC83 has a buffered output, the buffering accomplished with special bipolar transistors that have tubelike qualities.

The second stage is similar to the 610T and 250, with a differential pair loaded with a DMOS current source. Rather than using a 6550, the output tube drivers are new Silicon Carbide (SiC) JFETs, which give the driver stage more headroom. The output drivers are bootstrapped by the output (both in the drain and source), providing even more headroom during large signal swings, with reduced input capacitance.

Using JFETs for drivers also allows each tube to be biased individually: each tube has its own servo.

Output tubes are new KT170s, which have increased plate voltage margin, peak cathode current, and plate dissipation. They sound wonderful, with great musicality. In a properly designed circuit, the KT170 provides an elevated level of performance that is unequaled.

The power supply features solid state regulation for the front end and tube regulation (6H30 and 6550) for the output tube screens and driver stage. It also has a Pi filter using a large choke, reducing output stage supply ripple.

The 330M is a fully-balanced amplifier, from input to output. Operation is Pentode only because this offers the highest performance. The rear panel includes balanced XLR and single-ended RCA inputs, 8Ω and 4Ω output taps, 12V Triggers, RS-232 control, tube hour meter, 20A IEC, and fan speed adjustment.

In addition to the GhostMeter®, the front panel includes Power, Meter light adjustment, Tube Monitor, and a reduced voltage standby mode to preserve tube life while allowing quick startup

The Reference 330M is not Audio Research’s largest amplifier, it is our best ever. The presentation is vivid, immediate, and relaxed at the same time, with a musical completeness. Bass extension, control and weight defy its topology. To experience music through the 330M is the only way to appreciate how it serves the performance.