A turn-on circuit prevents sudden thumps and damage to components from the…
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The No.431's dual-mono design means that the amp has a separate power supply for each channel. Each power supply
includes a low-noise, 660VA toroidal transformer and two triple-bypassed, low-equivalent-series-resistance 24,000µF, electrolytic capacitors. Heavy bus bars of oxygen-free copper and high-frequency power-supply bypass components are used to lower the No.431's power-supply impedance. The amplifier can draw 15 amperes at 120V from the mains when driving a 4 ohm load to its full power rating of 400Wpc.
Sidebar 1: Specifications
Description: Solid-state dual-mono power amplifier. Speaker connections: four Madrigal-designed speaker binding posts. Input connections: two 3-pin XLRs, balanced; two RCAs, unbalanced. Other connectors; two 1/8" mini-jacks for remote turn-on; one RS-232 port on RJ-11; two Mark Levinson communication ports on RJ-45. Output power: 200Wpc into 8 ohms (23dBW), 400Wpc into 4 ohms (23dBW), 20Hz–20kHz, <0.5% THD (FTC); not rated into 2 ohms or for bridged operation. Frequency response: 20Hz–20kHz, ±0.5dB. Input sensitivity: 130mV for 2.83V output, 1.82V input for…
Sidebar 2: Associated Equipment
Analog source: Linn Sondek-Lingo turntable, Linn Ittok tonearm, Spectral phono cartridge; McIntosh MR-78, Sony ST-5000, Day-Sequerra Reference FM tuners.
Digital sources: Krell KRC-28 CD player, Sony SCD-C555ES multichannel SACD/CD player.
Preamplification: Krell KCT, Mark Levinson ML-7 (with L3A moving-coil phono cards) preamplifiers; Margulis phono section; Duntech MX-10 head amplifier.
Power amplifiers: Mark Levinson ML-2 monoblocks, No.334; Krell FPB 600c; Bryston 14B-SST.
Loudspeakers: Revel Ultima Salon, Quad ESL-989.
Cables:…
Sidebar 3: Measurements
Before measuring an amplifier, I run it for an hour at one-third power into 8 ohms with both channels driven. This subjects an amp with a class-B output stage to the maximum thermal stress. The chassis of the Mark Levinson No.431 was very hot at the end of this period, and its internal heatsinks were way too hot to touch. That they are just adequately specified, however, was indicated by the fact that the amplifier shut itself down after 62 minutes of running at one-third power, the front-panel LED flashing red. After it cooled down, the No.431 allowed itself to…
The patter of the snare drum began softly and I leaned forward in my seat. Avery Fisher Hall fell silent as Riccardo Muti led the New York Philharmonic in Ravel's Boléro. Ravel once described this masterpiece as "lasting 17 minutes and consisting wholly of orchestral texture without music—of one long, very gradual crescendo." Though the hall was silent and expectant, the stage was packed with musicians waiting for...what? To gradually join in, one by one and layer by layer, to drive that gentle but relentlessly mounting crescendo. Ravel accomplished this by "having solo instruments play the…
The crossovers have been designed as second-order electrical and fourth-order acoustical slopes, with a "Linkwitz-Reilly or Butterworth squared philosophy," notes Smith. He juggled the midbass drivers' mass and enclosure volumes and the values of the crossover series capacitance to get a third-order corner for the 100Hz high-pass subwoofer crossover. The midbass drivers cross over at 300Hz to the upper midrange drivers, which in turn cross over to the tweeter at 3kHz. The rear tweeter has a first-order climbing response from 2kHz to 9kHz, and flattens between 9kHz and 20kHz.
The XA90ps's…
The Snells faced the full length of my listening room, which is 26' long, 13' wide, and 12' high, with the lower part of the semi-cathedral ceiling above the left loudspeaker. The back of the room opens into a 25' by 15' kitchen through an 8' by 4' doorway. This large listening area—over 5000ft$s3—often causes two-way speakers to strain when pushed, but the Snell XA90ps produced high output without apparent distortion. Its stated voltage sensitivity of 90dB/2.83V/m is higher than the range of speakers usually reviewed by this magazine, allowing medium-powered solid-state amplifiers such as…
All audio products have their areas of strength and weakness—even one as well designed as the Snell XA90ps. To better evaluate the XA90ps, I used a variety of loudspeakers, some much more expensive—such as the older Snell Acoustics Reference Type A ($18,000/pair) and the Revel Salon ($15,000/pair). After lengthy listening sessions with these products, which twice or thrice as much as the Snells, I could detect differences—only on some program material—in soundstage depth, transparency, and freedom from compression. The $7000/pair Snell is obviously a highflying performer.
The Snell…
Sidebar 1: Specifications
Description: Four-way floorstanding loudspeaker with 5-element "Expanding Array" line source and rear-firing tweeter. Integrated with internally powered, dual-driver subwoofer with reflex alignment. Drive-units: 1" (25mm) aluminum-dome tweeter, 1" (25mm) rear tweeter, two 2.5" (60mm) midrange drivers, two 6.5" (160mm) midwoofers, two 10" (250mm) subwoofers powered by internal 300W amplifier. Crossover frequencies: 100Hz, 500Hz, and 2.5kHz (9kHz for rear tweeter). Crossover filters: 2nd-order electrical, 4th-order acoustical. Frequency response: 32Hz-22kHz, ±3dB…
Sidebar 2: Associated Equipment
Analog sources: Linn Sondek LP12 turntable with Lingo power supply and Ittok tonearm, Spectral moving-coil cartridge. Tuners: Day-Sequerra FM Reference Classic, Rotel RH-10, Fanfare FM-1, Magnum Dynalab MD-108. Sleuth 205 RF amplifier.
Digital source: Krell MD-1 CD transport, Adcom GDA-700 D/A processor.
Preamplifiers: Mark Levinson ML-7A, Duntech MX-10 head amplifier.
Power amplifiers: Mark Levinson No.331, Bryston 7B-ST monoblocks.
Reference Loudspeakers: Snell Type A Reference system, Revel Salon, Acoustic Research AR-1.
Cables:…