Sumo Polaris II power amplifier
Which brings us to the amp in question: the Sumo! Now, what picture pops into your head at the word "Sumo"? For me, it's two words: BUTT CHEEKS. I see huge, rolling, shuddering butt cheeks spilling out of black cotton Pampers while two Japanese Michelin Men alternately hug and gut-slam each other out of the ring and solemn judges in identical black business suits seated at the dais score what looks like the dancing hippos scene from Fantasia. I see tushes the size of Land Rovers, with laughing dimples deep enough to store grain. Lower-case letters simply don't do my mental image justice; I see BUTT CHEEKS.
So what does all that have to do with the $799 Sumo Polaris II amplifier, you ask? Quite a bit, actually. The words butt and cheek figure strongly in the sonic character of the amplifier. But first, the diapers.
Externally, the black brushed-aluminum chassis looks very solid, with the gold-lettered words "Sumo," "Polaris II," and "MOSFET" flanked by two wide rack handles. On the backside of the Sumo can be found the usual 5-way gold-plated binding posts, fuse holders, and detachable IEC-style three-prong AC cord. Looking at the gold-plated RCA input jacks, I was surprised at such a cheap-looking part on an otherwise well-built amp; closer inspection revealed these to be very good jacks indeed, with an internal spring that grips the RCA pins tightly. In comparison, the RCAs of the similarly priced Adcom GFA-555 II I had on hand, while more impressive-looking, had extremely low contact pressure and offered almost no resistance to the insertion and removal of interconnect cables. RCA plugs and jacks are already less than ideal for audio signal interconnection; high contact pressure is mandatory for good sonics and reliable operation.
The interior of the Polaris is modest, with decent components (footnote 1) and soldering work. A couple of things bothered me about the construction and wiring, though: first, many of the connections in the signal path and power supply are made with tin slip-on connectors. I would have much rather seen good soldered connections here, especially in the audio signal path. For example, the hookup wire carrying the output signal to the 5-way binding posts is connected to the board with these low-grade tin slip-on connectors; I question the benefit of high-quality gold-plated binding posts when the entire music signal has just passed through a cheap tin-tin contact junction. The other anomaly I found was with the output wiring's layout; each channel's output MOSFETs are mounted on the opposite side of the board to their output binding posts! This means that the hookup wires taking positive signals to their respective posts travel the entire width of the board and crisscross each other in intimate proximity.
Contrast this with the Muse Model One Hundred, which dispenses with output wiring entirely; its air-cored output inductor is the output wiring, with one end soldered to the board and the other soldered to the output binding post. Finally, the owner's manual states that the Polaris's inputs are AC-coupled with Mylar caps shunted with polystyrenes; I saw a single 2µF Mylar cap per channel, with no bypasses. Needless to say, even with a good polystyrene bypass cap, Mylar is hardly the best-sounding dielectric to use as the input coupling cap. Without a bypass, it will surely degrade the audio signal as compared with the high-quality Wonder, Sidereal, and Rel polypropylene caps used by most high-end manufacturers. Sumo shouldn't have scrimped here.
The Polaris's circuit couples an all-discrete bipolar class-A input stage with a MOSFET output section. Sumo's "TL" circuit, said to provide Transconductance Linearity, is employed to improve performance without resorting to high levels of negative feedback. In addition, a slip-on connector can be switched inside the amplifier to convert it to bridged mono operation; according to the manual, this provides 400W, with no load specified. As I only received one Polaris, my audition was of the amp in stereo mode only.
The listening setup remained the same as with the other amps on review. My self-modified Philips CD-50 fed my buffered passive preamp, this connected to the amplifiers under review. Interconnects and speaker cables were Straight Wire Maestro. Speakers were either Spica Angeluses or Thiel CS1.2s; all line-level gear was plugged into the Audio Express NoiseTrapper Plus.
Now, what of the significance of "butt" and "cheek"? These seemingly ordinary words take on great import when discussing the sonic characteristics of the Polaris, as they represent the opposite poles of its performance axis.
First, the good news. In my "Audio Glossary," "butt" means bass, and this is where the Polaris shines brightest. Like the Adcom GFA-555 II, the Polaris has very deep and tight bass, with excellent pitch definition and clarity. On "Big Enough," the first track on Keith Richards's Talk Is Cheap (Virgin (footnote 2) CD 7 90973-2 (footnote 3)), there's some powerful kick drum courtesy of Steve Jordan, along with some truly demented bass throb'n'gurgle from the master his own self Bootsy Collins. Through the Polaris, the bass was deep and taut, with excellent control and detail. I felt the bass of the Polaris to be only slightly more diffuse than that of the Adcom, and on a par with the more expensive Muse. In addition, the deep bass "ambience" noise at the beginning of the Cowboy Junkies' Trinity Session was at once imposing and solid. So the Polaris has definitely got its butt covered; what of the cheek?
Footnote 1: I did see two 741 op-amps; these appear to be part of the servo circuit that prevents DC offset on the outputs.
Footnote 2: I think it's hilarious that, of all people, Keef Riff-hard is on Virgin Records!
Footnote 3: One of the few studio rock recordings I know of with a realistic and live drum sound; guess it pays to let the drummer co-produce.