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Plinius SB-300

Dispelling class myths

By Michael Wong

June 2004

Plinius SB-300 power amplifier. $9480

For many audiophiles, the Class A amplifier has been the Holy Grail. Battleship build quality, heavy bulging heatsinks, hot running, lowish power, low electrical efficiency, expensive to buy but (usually) excellent sonics.

The year 1987 saw talented designer Gary Morrison (Craft Audio) joined forces with Peter Thomson of Plinius and begat a modern day Class A amplifier dynasty, beginning with the SA-50, leading to the mighty SA-250 and their latest take on Class A, the SA-102. These highly acclaimed amplifiers put Plinius on the map with audiophiles worldwide.

In 2003 the company was approached by an American home theatre speaker specialist who required a good sounding, high powered, affordable amplifier that could be used in multi-amplifier installations.

Olde World class from the New World

The SB-300 was the result. It shares the same physical size as the SA-102 and the same brutal, pre-Odeon visage: 38kg of square-jawed solid construction, meaty carry handles, large heatsinking on either side, capped with heavy aluminium top and bottom plates.

The front panel is a little sparser than previous Plinius amps with only a power on/off switch and bright blue power LED. Two additional LEDs indicate standby status and a warning light indicating error condition in the amp. eg. clipping, blown fuse.

The rear panel has a simplified Amplifier Configuration Selector offering only RCA unbalanced or XLR balanced inputs. Four pairs of large, heavy duty binding posts are offered for speaker connection with bi-wire option. A ground lift switch, IEC mains socket and 12V trigger terminals complete the rear panel.

Internally, the circuit topology is basically the same as the SA-102, with the inclusion of larger 550VA toroidal transformers and twice the number of output devices. A radical departure is the adoption of cooler running, more efficient Class AB operation.

This powerhouse produces 310 Watts per channel into 8 ohms, 470 Watts per channel into 4 ohms and a whopping 100A of peak current. This is ample for any domestic loudspeaker and more than enough to keep my Magnepans happy.

Symphony in AB

Previous Plinius designs have elicited mixed reactions amongst listeners. The wide dynamic capability and powerful, tuneful bass, warmish, tube-like tonality and good soundstaging captivated but the highs could be problematic. In modest systems they sounded sweet, if a bit laidback and lacking in the life and airiness of the best amplifiers. The high octaves had a grainy texture that was system and listener dependent - akin to a sonic version of the dreaded "screen door" effect on poor LCD based projectors.

The SA series needed a long warm-up time (think weeks rather than days) before the highs would smooth out. The SB-300 doesn't have this foible and sounded good straight out of the box. Using Well Tempered, Marantz, Denon and Nakamichi sources, with Krell and Plinius preamplification, produced enticingly, musical results.

The soundstage was realistically sized, with three dimensional images, transparent enough to "see" all the way to the back of the stage. Very good reproduction of low level detail, ambience retrieval and dynamic ability enough to handle the most demanding of recordings aided the illusion, reinforced by authority and control.

Gone is the upper octave texture of the SA amps, replaced with a sweet high end, free of grain and glare, natural and gentle on the ears but not obscuring any detail.

Like the M8 preamplifier (which provided a perfect accompaniment), there is a tonal continuity from the rejuvenated highs, through the full bodied midrange and onto the powerful, tuneful bass. This is neutrality with just a hint of warmth.

It's not perfect though, compared to some of the best like Krell, Spectral and Jadis, there's room for a little fine tuning. Bandwidth is modest for a solid state amp, the highs are still not as airy as some, transient response is a tad soft, there's not quite the speed or immediacy of more expensive amplifiers. But these are minor quibbles, at this early stage of its development, the SB-300 is already competitive with the best.

Full circle

Over twenty years ago the first Plinius amplifier was a modestly powered Class AB amplifier. Plinius have returned to Class AB operation to produce an amplifier of astounding performance. Forget that it is not a Class A design, forget that this was originally a home theatre design, as the SB-300 reproduces music with a fidelity comparable to the best amplifiers. And with its home ground advantage, it is available at a reasonable cost.

In my experience this is the best sounding Plinius amplifier yet. With Class AB sounding this good, is there any need to persist with Class A inefficiencies? Highly Recommended.