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The Orpheus was, however, unusually effective in keeping the soundstage from clustering inside my head. It wasn't completely successful in this—no headphones in my experience have been—but the soundstage seemed less of the clothesline-between-the-ears variety than is typical, extending instead from my left ear, across an arc just in front of my nose, then around to my right ear. This is more a matter of spectral balance than of any signal manipulation. The diffuse-field compensation referred to in Sennheiser's specifications refers to the design of the earpieces themselves—no electronic…
Sidebar 1: System
Unless otherwise noted, the Sennheiser headphones auditioned here were driven from the analog output of a Krell Reference 64 D/A processor. The transport was a Krell DT-10, connected to the processor by ST optical link with ST sync lock. The interconnects between the processor and headphone interface units were AudioQuest Lapis Hyperlitz, alternated with TARA Labs RSC where noted.
Comparison products included the Stax SR-Lambda Pro Classic, the Koss ESP/950, and Sennheiser's own HD-580 driven by the HeadRoom Supreme dedicated headphone amplifier.—Thomas J.…
Sidebar 2: Specifications
Sennheiser Orpheus HE 90 headphones: Open-back, diffuse-field compensated. Transducer principle: electrostatic, push-pull. Frequency response: 25Hz–75kHz, –3dB. Distortion: <0.01% at 94dB, <0.1% at 110dB. Maximum sound pressure level: 118dB. Bias voltage: 500VDC.
Weight (excluding cable): 12.9oz (365gm).
Orpheus HEV 90 amplifier: Tube headphone amplifier (not available separately) with on-board D/A processor. Frequency response: 10Hz–20kHz, –0.25dB. Distortion (1kHz): <0.01%. Input sensitivity: 400mV. Input impedance: 10k ohms. S/N ratio (unweighted…
James Bongiorno, the engineer behind the Sumo Andromeda, has enjoyed a long and colorful career as an audio amplifier designer. He has cast himself at times as an enfant terrible, exploding at audio critics and running scandalous advertisements (footnote 1). His best-known amplifier is the Ampzilla, produced by Great American Sound, but he also designed the Dyna 400. Currently Jim is living on a boat and serving as part-time consultant to the Sumo Company.
When the recession hit high-end audio in 1978–80, Bongiorno designed cost-effective versions of his original Sumo amplifiers…
Sidebar 1: 1984 Measurements
The Andromeda measured less than 0.028% Total Harmonic Distortion plus Noise (THD+N) at its rated power into 8 ohms, and less than 0.053% THD+N into 4 ohms at 324Wpc. The amplifier could not produce more power at 4 ohms, going into mutual conduction when pushed further. (Mutual conduction occurs when the complementary output devices (which normally work in turn) conduct current simultaneously, and thus work against one another, behaving like a partial short circuit across the power supply.) This was evidenced by a sudden increase of current draw, which…
Thomas J. Norton reviewed the Sumo Andromeda II in June 1991 (Vol.14 No.6):
The two-channel stereo amplifier is still the most typical configuration found in most systems, and the Sumo Andromeda II sticks with that convention. While the monoblock is becoming more popular, there's no free brunch; monoblock design results in higher costs to the manufacturer and thus to the buyer, all else being equal.
The Andromeda II is a pure complementary design using full-wave, balanced bridge circuitry. What this means for the user is that there are no common grounds at the output of the…
Sidebar 2: TJN's 1991 System
Associated equipment used in auditioning both of these amplifiers consisted of the Oracle Delphi Mk.IV turntable with SME V tonearm and Dynavector XX-1L cartridge, Sony CDP-X77ES CD player, Wadia WT-3200 transport and DigiMaster X-64.4 D/A converter, and Rowland Consonance preamplifier. Loudspeakers were the Apogee Stages, B&W 801 Matrix Series 2s, and Snell C/IVs. The amplifier was also briefly auditioned through the Nestorovic Type 5AS Mk.IIIs and the PSB Stratus Golds.
Interconnects were AudioQuest Lapis and Cardas Hexlink (the latter from…
Sidebar 3: Andromeda II Measurements
A more limited spectrum of tests was run on the Sumo than is usually the case because its floating ground requirement was incompatible with some of our test equipment. As can be seen from fig.1, the Andromeda II has only a very slight rolloff at the frequency extremes. There was a slight mismatch in gain between the two channels: an insignificant (in practice) 0.3dB. The 1kHz input impedance measured 42k ohms. The output impedance was below 0.06 ohms up to 1kHz, rising gradually to a maximum of 0.09 at 20kHz.
Fig.1 Sumo Andromeda II,…
Thomas J. Norton reviewed the Sumo Andromeda III in May 1996 (Vol.19 No.5):
Volume VII of Stereophile. That's a long way back. The Orwellian year of 1984, to be specific, and it was in Vol.7 No.6 that we reviewed the original Sumo Andromeda. Back when a home computer meant an Apple II (remember Apple?). Back when Home Theater meant Uncle Bill doing Karaoke without the oke (it hadn't been invented yet).
There's nothing like staying power. Apple is now an endangered fruit, and Uncle Bill still can't remember the words to "Lolly Pop," but the Sumo Andromeda lives on. Now in its…
Sidebar 4: TJN's 1996 System
The system I used in evaluating the Andromeda III consisted of the Denon DP-S1 CD transport, Mark Levinson No.36 D/A converter (the two linked by a Kimber AGDL coaxial digital cable), and a Jeff Rowland Design Group Consummate preamp. All auditioning took place in my (approximately) 26' by 18' by 11' listening room. The loudspeakers used were the Energy Veritas v2.8s. Preamp–power-amp interconnects were Cardas Hexlink (unbalanced and balanced). The loudspeakers were bi-wired using a single-jacket, bi-wire–configured pair of Monster M1.5 cables.—Thomas J.…