Sumo Andromeda power amplifier

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. These included the $750 class-A Model 9 and the $899 Sumo Andromeda. These second-generation Sumo amps present a common appearance—a tall, shallow chassis attached to a rackwidth, 5mm-thick front plate with massive handles. Fortunately they do not include the noisy fan found on earlier Sumo products—a major improvement. Fans effectively diminish an amp's signal/noise ratio (unless one runs the amp in another room).

Because its output circuit is configured into a full-wave balanced bridge, the amplifier has no common grounds except at the inputs. The unit's recessed banana-jack speaker terminals underline the importance of avoiding ground connections at the output, such as might occur with speaker switchers or headphone boxes. Bongiorno also designed the Andromeda without current limiters, using instead a single 7.5A Slo-Blo AC fuse mounted on the rear panel and 4 quick-blow, 7A internal (and hard to reach) fuses to protect the amplifier.

Sumo recommends that an outboard RC circuit be connected between the Andromeda and certain electrostatic loudspeakers. These kinds of speaker loads function like a short circuit at the subsonic frequencies of record warps (due to the decreasing impedance of inductors at low frequencies), putting an enormous strain on an amplifier. Sumo's president, Richard Pley, reports that no problems have arisen in the field from driving electrostatics, but I was unable to audition the Andromeda on an electrostatic.

Sound Quality
How does the Sumo Andromeda sound? It produces a surprisingly smooth, transparent sonic texture. Stereo imaging is exceptional, with outstanding inner detailing. In particular, the Andromeda is capable of generating a very wide soundstage while maintaining clear delineation of instruments and voices. The unit also proved to be much less harsh or bright during overload than is my Threshold Stasis 3 (footnote 2), without showing the overly mellow sound or slight loss of detail found in the VSP Labs 150.

On the Snell A/III speakers, the Andromeda showed tremendous midrange smoothness, with great separation of instruments and voices when using the amplifier in a biwired mode (see the Snell A/III review in this issue). In particular, it rendered the brass in an appropriately aggressive and unsettling manner, for example during the first movement of Stravinsky's Rite of Spring (Telarc CD-80054), but with none of the white hot, overbright glare heard from many other solid-state amps.

Yet the Andromeda does not sound artificially sweet or smooth; it simply adds little brightness of its own. The amp's low end is very decent: solid and dry, without the fullness of the VSP or the thunderous power of the Mark Levinson ML-9. Only the ML-9 significantly bettered the Andromedain very deep bass performance, but at three times the price. In my opinion, the Sumo runs a close sonic second to the ML-9 or the $3495 Spectral DMA-lOO. Performing at just below this class of amplifiers, the Andromeda is clearly a bargain.

What is important to the consumer is Bongiorno's implementation of a hig-end amplifier design at a relatively low cost. Bridged output circuits clearly can be made to sound very good, and offer extra reliability for bipolar output transistors. The Sumo Andromeda's low price tag, high power, clever design, and outstanding sonics on dynamic loudspeakers makes it a real find in the present day marketplace of "me-too" basic amplifiers. It is one of my favorite amplifiers for driving Dahlquist DQ-l0, Snell Type A/III, or, with care, Spica TC-50 loudspeakers. The Sumo amplifier represents an audio "best buy" and I recommend it with enthusiasm.—Larry Greenhill

Footnote 1: The most sacrilegious was a full-page cartoon of a gorilla (the symbol of his former Great American Sound amplifier products) nailed to a cross in an advertisement which appeared shortly after Bongiorno left GAS.

Footnote 2: The Stasis 3 is two generations previous to the Threshold S500/II that shows up in this issue's "Recommended Components."