Mark Levinson No.331 power amplifier
The earlier No.20-series Mark Levinson stereo amplifiers were based on the company's former Reference monoblock, the $14,950/pair 100W RMS No.20 amplifier, first introduced in 1986 and brought to final "20.6" level in 1992. I reviewed the No.27 back in 1990 (Vol.13 No.6 with measurements in Vol.13 No.7). Costing $3795 at the time, this amplifier featured a combination of smooth midrange, excellent imaging, and a light, highly defined, transparent treble. The No.27's treble and midrange sweetness offset the treble dryness in the Quad ESL-63 electrostatics I use for reference speakers, so I purchased the No.27 review sample. Even so, it had its limitations, retaining the exclusive Mark Levinson CAMAC input connectors, requiring the company's interconnect cables, special CAMAC-to-RCA adapters, or a re-tipping of interconnects with CAMACs. I also found it to have less apparent bass extension than did other top solid-state amplifiers in level-matched listening tests.
In 1992, the '27 was replaced by the No.27.5 ($5495, reviewed in July 1993, Vol.16 No.7). Features included "0.5" circuit boards, 10 lbs additional weight, RCA connectors, a wider chassis and faceplate, and a $1200higher price tag. Sonic changes included added low-frequency extension and dynamic range, but I found the Krell KSA-250 amplifier still edged out the 27.5 in gain-matched listening tests, with its greater solidity of deep bass, better control of soundstage depth, and lower-midrange forwardness.
Mark Levinson's No.20-something amplifier series went out of production in 1994, replaced by the No.33 Reference dual-chassis monaural pair and its derivatives, the Nos.331, 332, and 333 dual-mono amplifiers. I couldn't wait to compare the new No.331 with my vintage No.27.
What's new externally?
The Mark Levinson No.331 looks completely different from the 27-series amplifiers. The traditional Levinson black-cube-with-handles'n'heatsink look has been replaced with a two-tone silver and aluminum motif based on the styling of the No.33. The amplifier's faceplate is now a curved and machined piece of solid aluminum. This faceplate frames a smaller black panel on which are engraved the company and product names. The silver front and top plates provide a strong visual contrast to the large black heatsinks running along each side of the amplifier. These heatsinks, designed in-house, have a higher mass and structural rigidity than former units, and a lower level of mechanical resonance than those used in the 20-series amplifiers.
The No.331 is 4" deeper, 3" taller, and 27 lbs heavier than the No.27. Unlike the older amplifiers, the 33x series has no handles front or rear. Although Madrigal's Jon Herron told me that the amplifier can be hefted by one person grabbing the heatsinks, the manual wisely advises any new owner that "two strong people are required to unpack these amplifiers safely."
The front panel features a red indicator LED and an On/Standby button, the latter providing power cycling, with turn-on circuitry powered by an independent power supply activated when the unit is plugged into an AC source. When power is applied after the heavy, detachable AC cord is plugged in, the amplifier remains off. One press of the power button puts the amplifier in standby mode, as noted by the slowly flashing indicator. This activates DC to the voltage gain-stages from a separate winding in each channel's power-supply transformer. One must wait 10 seconds, then press the button a second time to toggle the amplifier between standby and full on. This delay, lengthier than found in most amplifiers, allows the in-rush circuitry to slowly charge the power-supply filter capacitors. An additional press of the button toggles the amplifier back into standby. To turn it full off, it's necessary to depress the button for one second, or until the power indicator goes off.
On the rear panel, inputs are made via single-ended RCA connectors or balanced XLR connectors. The amplifier is shipped with tiny U-shaped shorting pins inserted in the XLRs to allow unbalanced use; pulling out these pins allows for balanced operation. A socket for a conventional IEC standard power cord sits at bottom center of the rear panel (footnote 1), flanked by a pair of remote turn-on input jacks for systems that don't include a Mark Levinson No.30-series preamplifier.
Alternately, the No.331 can be controlled via separate back-panel communication ports by a "linked" Levinson 30-series preamplifier when the left port ("slave-in") is connected to the master port of the preamplifier. This allows for remote, one-button turn-on when linked to another Mark Levinson product equipped with the appropriate software. An additional five 33x-series amplifiers can be daisy-chained from the other port ("slave-out"). These links provide for remote turn-on from the preamplifier and for the preamp to display error conditions if they should occur in the amplifiers.
Footnote 1: The AC cable was made detachable in the No.331, whose maximum current draw of 18A is within the rating of the detachable IEC connector. The No.333, which can draw over 45A from a 120V AC line at full power when driving a 2 ohm load, has a nondetachable power cord.