Mark Levinson No.26 preamplifier & No.20 monoblock power amplifier JA April 1992
Madrigal Audio Laboratories launched their first new Mark Levinson product, the No.20 "reference" power amplifier, in 1986. This massive monoblock featured an output stage running in class-A up to 100W into 8 ohms, and full regulation of the output stage voltage rails. When I reviewed it in 1988 (Vol.11 No.5), I thought it one of the finest amplifiers I'd auditioned, particularly regarding soundstaging and low-frequency authority. (Stereophile subsequently bought the review pair!)
Madrigal's thinking about their "reference" products is that they should be capable of being upgraded as new circuits and technologies become feasible. Thus it was with the No.20: the AP-4 input and driver board, introduced in 1989, metamorphosed the No.20 into the No.20.5. In my September '89 review (Vol.12 No.9), I said that the 20.5 retained its position as the best amplifier overall I'd yet heard at that time.
Nothing stands still, however. The appearance of first the Audio Research Classic series of hybrid FET/tube amplifiers, then the Krell KSA-250, redefined, for me at least, the state of the art of amplifier design. Perhaps as a result of this intense competition for the Levinson 20.5 and its class-AB sibling, the No.23, Madrigal launched the $5900 Mark Levinson No.23.5 in 1991. While I was not a big fan of the original '23, finding its sound to be too vivid, I noted in my review (Vol.14 No.9) that the No.23.5 offered a more dynamic, better-defined view into the soundstage than the '20.5, which by comparison was too soft and rather veiled in the treble. The older amplifier's upper midrange/low treble also tended to sound rather grainy, particularly before being fully warmed up.
With the No.23.5 outperforming it, it was obviously time for Madrigal to rethink the No.20.5, the result being the Mark Levinson No.20.6 (footnote 1). The electrical differences between the two amplifiers are all contained on the new AP-5 module, which replaces the AP-4 behind the amplifier's rear panel. Slotting vertically into the mil-spec "Varicon" connectors on the '20.5's motherboard and held secure with new L-brackets, the AP-5 consists of two separate Teflon-dielectric printed-circuit boards attached to a full-depth heatsink and occupies virtually all the available chassis space. (A new insulating screen has to be attached to the rear of the RP-3 regulator pcb, which sits in front of the AP-5, to avoid inadvertent short-circuits.)
Before performing the upgrade on Stereophile's No.20.5s, I spent a weekend using them to drive the WATTs/Puppies via MIT's MH-750 Shotgun Terminator speaker cable (footnote 2). After using the Audio Research Classic 120s for a couple of months, I'd forgotten the awesome authority of the 20.5's low frequencies, which quite bely its 100W rating. At the start of "The Rhythm of the Heat" on Peter Gabriel's eponymous 1982 album, following the Ekome Dance Company's drum intro, there is a stupendous, spacey bass transient that rarely is as stupendous or spacious as I suspect it should be—unless you use the Levinson monoblocks, when it literally throws you back in your chair, gasping for breath, your flight reflexes cranked up to ten. But the amp's rather veiled treble was a letdown after the Classic 120's superbly transparent presentation.
I installed the AP-5 boards and let the amplifier bed in for 24 hours. The bias checked out okay after the upgrade, so I put on a spot of music—Barenboim's wonderful new Parsifal—and...
Couple the 20.5's effortless dynamics and bass extension, weight, and control with the soundstaging depth and lack of midrange grain of the ARC 120s, the detail, the transparency, the "You-R-there" presence of the No.23.5, and the musical ease of the real thing, and you'll get some idea of the sheer MAJESTY of this amplifier's sound. Madrigal has regained the gold with the No.20.6, in my opinion, easily the most musically pleasing solid-state amplifier I have ever had the pleasure to use. No.20 and '20.5 owners: You have no choice about what to do next.—John Atkinson
Footnote 1: A new pair of '20.6s costs $14,950. The upgrade from a pair of No.20.5s costs $2390/pair plus $560/pair for new faceplates; the upgrade from older amplifiers below S/N 1850 costs $3290/pair.—John Atkinson
Footnote 2: Preamp was the admittedly weird but wonderful combination of the McCormack Phono Drive EPS and Melos SHA1; sources were the fully loaded Linn and the VTL Reference DAC, driven by a Wadia WT-3200 transport.—John Atkinson