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What you see
The 330M's impressive array of 10 tubes is clearly visible through either its transparent glass front plate, on which an update of its classic watt meter appears in white, and through its open top. Because the fully balanced amp does not use heavy toroidal transformers, it weighs far less than you might expect for a component that's 19" wide, 10.25" high, and 21.5" deep. Most of its 101 lb resides in the rear. Handles on the front and rear panels make the 330M easier to lift than many other amps its size and weight.

Below the front meter and logo is a horizontal…

I measured one of the DeVore Fidelity Gibbon Super Nines that had been auditioned by KM; it had the serial number S915B112. I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone with an Earthworks microphone preamplifier for the farfield frequency behavior and dispersion measurements. I used an Earthworks QTC-40 mike for the nearfield responses and Dayton Audio's DATS V2 system to measure the impedance magnitude and electrical phase angle.

I performed a complete set of measurements on one of the Audio Research Reference 330M amplifiers (serial number 056438) with my Audio Precision SYS2722. The amplifier preserved absolute polarity, ie, was noninverting, with the balanced input and the 8 ohm and 4 ohm output transformer binding posts. However, the 330M inverted polarity with the single-ended input. The gain is specified as 26.3dB with the balanced input and 34dB with the single-ended input, both into 8 ohms. I measured 26.5dB and 32.5dB, respectively, into 8 ohms from the 8 ohm output tap. The gains…

Digital sources: dCS Vareèse five-piece music system, dCS Rossini CD/SACD transport; EMM Labs DV2i DAC, Meitner MA3 Integrated DAC; Innuos Nazaré Music Server and PhoenixNET network switch; Small Green Computer Sonore opticalModule Deluxe (2); Broadcom/Avago AFBR-5718PZ 1GB SX-SFP, Gen 5 Fiber Optic modules (2); Nordost QSource linear power supply (2); Sonore Audiophile Linear Power Supply; Synology 5-bay 1019+ NAS with Ferrum Hypsos linear/switching hybrid power supply; ASUS AX6000 and RT-AX88U Pro mesh routers and Netgear Nighthawk modem; Apple 2023 iPad…

Description: Tubed, fully balanced class-AB mono amplifier with 20A IEC connector, autobias, fan-speed control, tube hour meter, and monitor. Tube complement: Three matched pairs KT170 (Power Output positions V1-6), two 6H30 (Gain stage V7 and regulator driver V10), one 12AX7/ECC83 (Gain stage V8), and one 6550 (Regulator V9). Inputs: One pair XLR (balanced), 1 pair RCA (single-ended). Outputs: 4 and 8 ohm. Power output: 330W @ 1kHz 0.92% THD+N 10Hz–80kHz unweighted; 1W @ 1kHz 0.013% THD+N 10Hz–80kHz unweighted. Frequency response: (–3dB points at 1W) 5Hz–99.5kHz. Input sensitivity: 2.…

Analog sources: J.Sikora Standard Max Supreme turntable with KV9 tonearm and Aidas MC Tru-stone Gold Web cartridge.
Preamplifiers: Sugden LA-4, Rogue RP7 (line). Tavish Audio Design Adagio, Manley Chinook (phono).
Integrated amplifiers: Riviera Labs Levante, Unison Research S6 Black Edition.
Power amplifiers: Air Tight ATM-1 2024 Edition, Doshi Audio Evolution Stereo Amplifier, Rogue Audio Stereo 100, Elekit TU-888 monoblocks.
Cables: Interconnects: AudioQuest Pegasus and Firebird, Triode Wire Labs Spirit II (RCA), "Spirit 75" S/PDIF (RCA/…

Description: 2.5-way, reflex loaded, floorstanding loudspeaker with solid bamboo, plywood, and composite enclosure. Drivers: one proprietary 0.75" (19mm) textile-dome tweeter and two 7" (178mm) paper cone woofers. Frequency range: 28Hz–38kHz. Sensitivity: 91dB/W/1m. Nominal impedance: 8 ohms.
Dimensions: 37" (940mm, not including feet) H × 8.5" (216mm) W × 13.75" (349mm) D. Weight: 55lb (25kg).
Finishes: Cherry, Mahogany, Mink.
Serial numbers of units reviewed: S915B112 (both).
Price: $9990/pair. Approximate number of US dealers: 20. Warranty: 5…

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