Music Reference RM-9 power amplifier RM-9 Mk.II
My last encounter with the RM-9 was in December 1989 (Vol.12 No.12, p.105). I was taken by its even tonal balance, imaging capabilities, and seductive midrangeespecially when outfitted with KT88sand gave it a strong Class B recommendation.
Now, almost five years later, Music Reference has released the Mk.II version, which, at least on paper, appears to contain only minor upgrades. That in itself is prima facie evidence that the basic design of the RM-9 was sound. The High End has a history of unleashing on an unsuspecting public productsprototypes, in effectwith all their design bugs and/or reliability problems intact. The underlying assumption has been that the consumer should be willing to participate in this involuntary "testing" program. Music Reference's Roger Modjeski, on the other hand, takes pride in doing his homework, and releasing a product only when it's finished.
Let's take a closer look at the Mk.II. The output power has been nudged from 100 to 125Wpc[an increase of 1dBWEd.]the new wood frame is more visually pleasing, and the On/Off switch is now rocker-style. The five-way binding posts are newthey're made of solid copper, have ¼" studs, and are altogether more pleasing to my sensibilities. The output-tube fuses are now top-mounted together with "Fuse-Out" indicatorsa major convenienceand the input/driver tubes are 6922s, tested by RAM Labs.
But the most significant upgradesthose in the power supplyare invisible. Capacitor energy storage, for instance, has been increased by 50%. Most significant, according to Roger, are the dual chokes that have been added to the power supply beyond the existing filter networka filter dedicated to each channel. These chokes not only improve the filtering action, but also serve to improve right/left channel separation. Best of all, the RM-9's retail price is almost the same as it was in 1989: $2950 in oak with an EL34C output-tube complement. Additional finishes and output-tube complements (eg, KT88s) are available as options.
I used the Mk.II to drive the Audiostatic ES-100 electrostatics. My sonic expectations were modest at bestafter all, from the look of the upgrades, there was little to suggest any quantum leaps in performance. But, holy cow! The Mk.II had incisive imaging, almost magically fashioning a startlingly transparent soundstagethe likes of which I've come to expect only from the world's best power amplifiers. Harmonic textures were sweet, liquid, and imbued with remarkable timbral accuracy; low-level resolution was on a par with that of any amp I've tried with the Audiostaticsincluding some much more expensive world-class amps; and the lower mids were well-fleshed-out tonally, with a full spectrum of dynamic expressiveness.
I quickly decided that the Hi-Gain position (lowest-feedback setting) was the most incisive spatially, and did all my critical listening with that configuration. In order to better assess the RM-9's lower-octave performance, I added the Audiostatic SW-100 woofer panels to the ES-100s. There was plenty of bass drive and transient finesse, and the upper bass was tonally full, with a gutsy, dynamic voicing that lent credibility to cello and double-bass reproduction.
I told my wife, Lesley, that she had to hear the ultimate Lesley testLesley on Lesleywith this new amp. Listening to Anyone in Love (Lesley & the Santa Fe Sound Machine, Vital Music VF003), she was astonished by the accuracy of the harmonic palette and sheer verve projected by the RM-9.
"This is the best amp I've heard yet on these speakers," she opined. I nodded.
"Hang on to this one," she said to me. Right.
Roger had been kind enough to supply me with two matched quartets of Chinese KT88C$s1 tubes, so I proceeded to audition the RM-9 with them installed. The RM-9 sounded drastically different with the KT88 complementas if a giant searchlight had flooded the upper midrange, clarifying and purifying harmonic textures. Harmonic overtones were also more vivid, which showed off some of the magic of the KT88s. However, there was also a subtle, bright tinge through the upper mids and lower treble; nor were the lower mids and upper bass as fully fleshed-out. The bass balance was a bit lighter, and had a reduced sense of drive and dynamics. I changed back to the EL34s, which brought back a distinct rhythmic drive to the upper bass and lower mids, so I'll continue using them until I can try this amp with some genuine N.O.S. KT88s.
I consider the RM-9 Mk.II an authentic American classic. Forget the McIntosh 275 or the Marantz 8Bthey don't sound nearly as good. Despite its stereo configuration and modest size, the RM-9 is a genuine Class A contender.Dick Olsher
Footnote 1: The "C" designation is strictly RAM Labs', not the factory's. Roger thinks that disastrous early production has given the Chinese KT88 a bad reputation; and, while quality has improved, audiophiles' opinions have not. Still, he warned me that the KT88s may be more cantankerous than the EL34s; he was proven right when a lint short took out one of the B+ output-tube fuses. Contrary to popular belief, vacuum tubes are not manufactured in a clean-room, as are semiconductors, so it's quite possible for lint to enter the glass envelope during production. If a lint thread attaches to two electrodes, it provides a path for a discharge. While the discharge vaporizes the lint, thus purifying the inner volume of the tube, the current surge can cause serious circuit damageunless B+ output-tube fusing is provided.