Clarity, smoothness, 3-D imaging and soundstage

Bass is good, but not tight

This is an excellent value in a 125 Watt tube amplifier. I thought I needed more power than the 60 W my great old Audio Research D70 MKII was providing for the Audio Physic Libra speakers I purchased. The RM9 MKII was a terrific choice. It had EL34's when I bought it and it sounded sweet and open. I ended up putting in Svetlana 6550C's, which have much more authority, better bass and are quieter. The three position feed back switch is interesting to fiddle with. I ended up using the high position, least feedback, as it seems to have the best bass and detail. Biasing is very easy and I have not had any significant drift. This is a terrific component that competes well against much more expensive amps.

Similar Products Used:

ARC D-70 MK II

High output, low maintenance

Singular application: for insensitive speakers only

This is a review on the Music Reference RM9 Mk II tube amplifier. Its design is based on the EL34 output tubes with 4 for each channel, sporting 125wpc into 8ohms, and it does have 6- and 4ohms taps. The owner's manual provided guideline for using other varieties of output tubes, like the KT-88 and 6550. It retailed for $3,495. In 1995, Stereophile magazine rated the EL34-based design an Class A component, and compared it favorably with the McIntosh 275 and 225, if it is operated in the High input level mode, which induced the least negative feedback.

Associated equipment:

CEC TL1 belt-drive CD transport (via Wadia ST link to)
Wadia 27 D/A converter (via Granite Audio model #470 interconnect to)
Music Reference RM9 Mk II tube power amplifier, Golden Tube Audio SE-40, Monarchy Audio SM-70 (via Cardas Quadlink 5 to)
Celestion SL700's or Klipschorns.

For my review on Celestion SL700, see http://www.audioreview.com/reviews/Speaker/product_7045.shtml
For my review on Granite Audio model #470 interconnect, see http://www.audioreview.com/reviews/Cable/product_3709.shtml

The RM9 Mk II is my first return to tube amp after a brief association with solid state designs. The solid state I used was the Krell KST-100, and before that, I used an Audio Research D76a tube amp. I still kick myself for selling the D76a. My only comfort now comes from the fact that the RM9 sounds more dynamic than the D76a, and is superior in the ease of maintenance.


Speakers: Celestion SL700 (October 1992 to April, 1999)

For over 2 years, the RM9 was used to drive the Celestion SL700, before the arrival of the Klipschorns.

Performance-wise, the RM9 surprises me with the dynamics and drive for a tube amp. While it doesn't sound exceptionally silky, like from some tube designs, it is nevertheless a tube amp. As such, it softens the harshness of many digital recordings to a significant degree.

There is an input level selector switch on the top panel, which raises the negative feedback from 10db in the High position to 15db at the Mid position, and finally 25db at the Low position. The best performance is to be achieved with the least negative feedback, which yields the most transparent presentation while providing the highest output. This coincides with Stereophile's finding. The RM9 is a superb fit with my Celestions; but a marginal match with my Klipschorns. A detailed and dedicated review on the Klipschorns will be done at a different place and time.

All my listening sessions were done with the RM9 at the High input level, which produced the least amount of negative feedback.

When driving the Celestion SL700's, the RM9 shone. At 125wpc, the RM9 was able to induce the most sonically intoxicating effects from the Celestions at their low efficiency of 82db/w/m. Whereas the Krell was equally capable of pushing the Celestions to wall-shattering levels, the RM9 accomplished the same feast with the most impressive reproduction of soundfields, unveiling the soundstage between and behind the speakers, making the presentation breathtakingly 3-dimensional. My 2-year association with the powerful Krell thus came to a happy end. I sold the Krell, then bought the Music Reference.

Solid-state amplifiers are renowned for their capabilities of rolling out the bottom octaves from speakers. The Krell KST100 was no exception, if not more so than the Music Reference RM9 Mk II in this regard is. The RM9, however, came very close in the bass area; but in doing so it brought out a whole array of sonic marvels, transforming the Celestions into world-class minimonitors. The KST100 was able to rock the room with solid, heart-shattering bass notes. The RM9 stopped short of the defining bass note of the KST100; but the overall, wholly rendition of music and sounds captured me, so much so that it quickly became my top priority to enjoy the music first. The thought of the singular pursuit of certain aspect of sonic reproduction became outfashioned and unthinkable.

The design of the RM9 has much merit. First, it is extremely user-friendly. All the fuses for the output tubes are located next to the tubes for easy access. The biasing control for both the driver and output tubes are located on the top panel. Accessing it requires only a small Phillips screwdriver. Biasing level is indicated by LED's, with the optimum setting indicated in the owner's manual. This is an undisputed design triumph. The cost of retubing the whole unit would cost approximately $400. While the output tubes are estimated by the manufacturer to last over 100,000 hours, in my experience, however, retubing is necessary every 3 years.


Klipschorns (April 1999 ~)

The Klipschorns are totally different in every respect. At a sensitivity level of 104dB/w/m, it theoretically plays loud with only 1wpc. There is a school of thought that says the higher the power the better - not for the volume, but for the driver control. I am sure the same principle could apply to the Klipschorns in some ways; but the RM9 is an high-powered tube design, best coupled to speakers with low to medium efficiencies, like the Celestions. Under such circumstances, the high output of the amplifier becomes a poor match for the Klipschorns. Tubes are quiet when playing, noisy when idling. And in the case of the RM9, the Klipschorns exhibited audible noise level when idling. It is perhaps so because of its exceptional sensitivity.

In this instance, the RM9's design makes the Klipschorns blast.


Conclusion

The Music Reference RM9 MK II's high-powered performance is best suited to low to medium sensitivity loudspeakers. In this world of powerful solid-state amplifiers, the RM9 is most welcomed. All roads lead to Rome. I believe eventually all well-engineered amplifiers, be it solid-state or tube, will eventually attain the ultimate goal for an amplification design: amplify the signal with no loss. When it happens, solid-state and tube will meet at an impasse where their sonic characteristics are indistinguishable. With the RM9 possessing the punch of a solid-state and the finesse of valve, I am hopeful of such a day.

The singular design flaw on the RM9 II is the rocker power switch, which failed twice on me during my ownership of it since summer of 1994. The replacement part costs $2 and it is not very hard to replace. It is just a wonder that the designer would couple such a poor switch with a fantastic amplifier.

4 Stars -- let's be modest !

Similar Products Used:

Audio Research D76a, Golden Audio SE-40