Solid State Power Amp Reviews

Having heard the No.334's strong bass response and dynamic contrasts, I couldn't wait to try Madrigal's MLC780 VG No.331.5 Update Kit on my own No.331 dual-mono amplifier. At $1950 it is an expensive modification, especially when you consider that the difference in retail cost between the No.334 and the discontinued No.331 is only $1000. Madrigal claims that the two cyanate-ester voltage-gain boards account for most of this cost. Besides these PCBs, the kit supplies a new black-anodized "No.331.5" nameplate for insertion into the front panel; a new rear-panel stick-on label stating "No.331.5, Factory Authorized Update," with the serial number; a Whia slotted 2.0x40 precision electronic tool for unlocking the XLR connectors; and instruction sheets with color photographs. Similar upgrades are available for the No.332 and No.333 amplifiers.

Madrigal's David Nauber explained that the update kit was designed for dealer installation, a polite hint that I ignored as I requested a kit. (Installation by an authorized Madrigal dealer actually is mandatory or the warranty will be voided.) But after four hours of work, three phone calls, and one trip to the hardware store, I had a functioning No.331.5. Swapping VG boards and front-panel nameplates was easy, but unscrewing and then re-screwing the 62 Allen-head bolts securing the top plate, output device covers, heatsink dress bars, VG boards, bottom plate, and front panel to install the replacement parts was demanding, risky, occasionally frustrating, and eventually rewarding.

Demanding? The job required a clean surface, excellent lighting, keen eyesight to seat the four sizes of Allen wrenches required, strong muscles to rotate the amplifier during the job, a Philips screwdriver, a 1/4" nut driver, and a power drill with a reinforced cutoff wheel and mandrel to notch a stripped bolt holding the powder-finished bottom plate to the chassis. The instruction booklet's photographs were excellent, and Madrigal's service staff was very helpful and most responsive by telephone.

Risky? The No.331's blue electrolytic filter capacitors held a sizable charge, even after the amplifier had been unplugged from the AC mains for two weeks. Working inside a metal chassis, using metal wrenches to unscrew metal bolts less than an inch from an electrolytic capacitor's positive terminal, and rescuing metal washers when they fell into the chassis provided lots of tension and drama. For safety, I covered the electrolytics with a rubber mat while working inside the chassis.

Frustrating? The screwposts of the new No.331.5 nameplate turned out to be too short to hold down my amplifier's on/off circuit mounting block—a standoff to keep the turn-on circuit away from the metal nameplate—so I had to reinstall the original (No.331) nameplate. Investigations back at Madrigal discovered that early-production No.331s (my unit's serial no.: 1114) used the No.33's thicker mounting block. The service department express-mailed me a thinner piece the next day, and the problem was solved.

Rewarding? For me, the cyanate-ester VG board's sonic improvements were worth all the effort. The added bass heft was heard right away when playing Massive Attack's Unfinished Symphony (Circa WBRX2). The soundtrack from My Cousin Vinny (Varèse Sarabande VSD 5364) had much more slam, punch, and drive, like Popeye after a fresh can of spinach. More transparent mids and highs, grain-free and open, were also present. All told, the update brought my old No.331 amplifier more than halfway up to the No.334's level.

However, the 331.5 kit did not transform my amplifier into a full-blown No.334. While certainly improved, deep synthesizer notes did not growl, shock, or surprise as they did when played over a gain-matched No.334—which produced a wider, deeper soundstage, greater dynamic contrasts, more headroom, and more transparent midranges than did the No.331.5. Owners who like the sonic performance of their No.331 but would like improved bass response will benefit most from this upgrade.—Larry Greenhill