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Plinius SB-301 MKII power amp

It is reassuring sometimes to test a piece of equipment which, substantially and at home, has exactly all the watts we want: and also far beyond.

A sort of tranquility that, at high volumes, raises us from the subtle anxiety of perceiving the start of the clipping in a musical peak or, at best, the timbric hardening that is a symptom of an audible distortion very unpleasant to our eardrums and to the loudspeakers coils.


The Plinius SB-301 MKII fits perfectly to this target since it is among the existing stereo amplifications that are more provided of watts: beyond 500 into 4 ohms, and capable, on paper, to drive any loudspeaker in whatever domestic environment.

The object is also a sort of bet for the New Zealander manufacturer who tries to come as closer as possible to the Plinius range top, the SA Reference model operating in pure A class, by designing a power amp operating in AB class, therefore technically disadvantaged as far as the control of the distortion is concerned. Another goal searched and achieved has been to offer a larger power supply than the SA-103 power amp, which cost and power are lower though, but preserving the very high refinement and fine grain that the SA-103 guarantees.

Hence, an electronic device that would set itself like a sort of crossover, at an intermediate cost between the other two class A amplifiers, with the same quality and very high skills of output power that are typical of the AB class amps.

The price is about 13,000.00 euro in Italy, not cheap but far from the products of many top competitors, some of which, I must say, with an exaggerate cost that makes raise the customer's expectations and mine for this test.


The SB-301, click here to download the brochure, in this new MKII version, has the same silver satin livery and it looks (and it is) imposing and heavy. The sensation of solidity is tangible and real, both under the manufacturing and operational point of view.

An internal relays acts as a timing device for the power on. It puts the machine in stand-by mode after a short interval signaled by the blinking of a LED on the frontal. When the LED is on the power amp is operational.

Inside we can see a good making level, good components if compared with the budget and a good engineering of the cards.

The power supply avails itself of two separate high power toroidal pieces, some bridge rectifiers and 6.800 microfarad electrolytic filter capacitors in a number of ten, with a consequent total capacity, considered the power at stake, surely not overmuch.

My impression is that this object communicates a sense of energy although the components - it is my personal opinion - are not up to selling price.


Nowadays, the scheme of the final stage of all the Plinius devices is rather unusual under the circuitry point of view. There are 32 NPN transistors, actually. You have to consider that in the push pull final stages, usually employed in the traditional modern amplifications, the NPN transistor is used with its complementary PNP so that the two semi-waves are amplified by the two complementary and symmetric transistors in order to cut down the distortions of the even harmonics.

Instead, in the Plinius, the two branches are amplified only by this last type, in a circuitry typology called "quasi complementary symmetry", as used to happened in the solid state power amps of more than forty years ago and before, when the PNP, a transistor whose base is fed with a negative polarity tension, was not been invented yet or was not yet satisfying in comparison with the older NPN and, by the way, the first complementary pairs were very expensive for the audio scope.

So, why this choice, today not anymore compulsory, which has some problems and, on paper, only one real advantage?

Let's say that some designers were and are convinced also today that such configuration of the final stage involves, against some problems that can be easily solved - on the Plinius for sure solved, considered as it performs - a certain advantage in acoustic terms. In fact, in the counterphase scheme, the direct consequence of let amplifying the two semi-waves by transistors that are not perfectly symmetric, is a sort of - moderate - increase of the distortion of the second harmonic, which effects are, most of all in a solid state, discretely positive, as there is a more correct harmonic structure of the total distortion with appreciable repercussions on the listening pleasure.

All this pertain to the personal beliefs that each designer has about how to get the best performances by using different solutions. Otherwise we will have the same amplifications, haven't we?

I think that the final user has not to worry about which implementation has been used. The important is that every piece has to be well designed and perfectly operating: and the Plinius SB-301 certainly is.


In conclusion, I would like to say that this amp is in AB class with a reasonable polarization current. It follows that, there is a certain warmth when the amp is operating, also due to the considerable number of final devices that have been used. Anyway, the first watts, how many it depends from the loudspeaker load, are given with the interdiction of the transistors, hence in A class.

This is very important because, in the majority of the real cases and mostly with speakers that have an impedance module not very low, the SB-301 can give all the advantages of this functioning class with medium volumes too.


Listening test

I have connected the power amp to my system at the place of the PassLabs XA 30.5 which, as it is known, gives 30 watts in pure A class and then commutes in B class giving about 200 watts into a load of 4 ohms with distortion levels that are still contained: a power value that in my listening room is quite enough, also considering the great current supply of the American power amp.

However, at very high volume levels, more fluidity and more emission facility is perceptible since the Plinius is more generous.

Practically, this amplifier satisfies all the requisites that a today's solid state of quality can offer in terms of undistorted power and clean sound, emission fluidity and timbric correctness and pleasure in listening.

We are dealing with a rigorous, solid amplifier with a well articulated harmonic structure, although inferior if compared with several tubes competitors and with the best, even if much more expensive, solid state realizations.


The first impression, always reconfirmed by successive listening tests, is a great sensation of sound cleanness, together with a remarkable timbric rigor, outcome of an emission linearity of great level.

An exception is, with some poor recordings or by using not very synergic cables, a slight hint of hyperventilation on the mid high range, sometimes too enlightened by an intense white light that can represents the strings not very fluidly, mainly in the orchestral ensembles where in some instances you may desire more sweetness.

The low range is excellent, very deep and linear, never pompous or not more controlled, but most of all quick in a natural way, not artifact or cut off, as sometimes happens in some solid state power amps, also famous.

For some aspect, it reminds me that one of the best ever Krell machines.

The mid low is very clean and controlled. It gives brilliance and harmonic vigor but, very important thing, for its high strictness it removes the reproduction of all these superstructures and timbric contaminations that dirty the sound emission and make less intelligible the instrumental structure, of which through the Plinius we perceive only the air and the notes that permeate it.

Thus, lots of particulars are available. And with a very high degree of listening easiness and transparency that, together with a remarkable care for the detail, let make the listener able to easily recognize in the musical program that is reproduced what entirely forms it, both for the instruments and the human voices.

This features make the Plinius an universal power amp since it has, besides the transparency and details skills, very useful in the small ensembles of acoustic music as well as in the baroque orchestral groups, that sound pressure and that dynamic attitude necessary both in rock and big orchestras classical music, where sometimes the power, but chiefly the dynamic, are not quite enough.

Another common aspect in the entire production of the New Zealander brand is the extreme refinement of the sound texture, absolutely without any grain and definitely neutral. The sound fluidity is so noteworthy that it never tires also during prolonged listening sessions with high volume levels, pushed by the desire of replicate the live event: I am talking of acoustic music obviously.


In a few words nothing is missing.


The image is very wide and deep, very precise in individuating the sound stages and in the focalization. Although turning up the volume, at least with my Martin Logan, there is a sort of sound gigantism that make lose the precision of the instruments contours.

In few solid state competitors, there is a slight room for improvement, but only in few more expensive products – Viola Audio and the Cello come to my mind, while so far I have never heard the new Pass brand products – starting from the SA Reference, which, I must say, has a light major harmonic caliber, together with some superior sweetness and subtlety.

Anyhow, everything is represented with an excellent quality in order to satisfy the solid state enthusiasts and who, regardless of the manufacturing technology of an amplifier, is looking for a sound without evident faults and without any listening fatigue. With the Plinius SB-301 you do not have to take a chance.



The Plinius SB-301 MKII is an excellent music machine, enough concrete to face whatever listening exigency, and with the capacity of conjugate the big output powers to a level of sound finesse achievable only with less powerful valuable amps.

I think the Plinius SB-301 represents a great tool able, without any doubt, to drive every kind of loudspeaker, although for some technical choices I suggest to prefer those systems that are not very demanding as for electric needs, I mean module and impedance phase, in whatever contest and with any musical program.

Therefore a damned universal object and so skilled to be considered a definitive object, considering the meaning this adjective has in the hi-fi world though.

I would match it with tube amplifiers and, although obvious, also to the best solid states exponents which could be the natural completion, mostly as regard as the timbric neutrality and the control.

Hence Plinius is, also with an intermediate product of its expensive list, like one of the best manufacturers of solid state electronics, perfectly capable of compete with the most qualified American and European productions.



Top Score ✳✳✳✳✳ ReMusic Sparks

Timbric: ✳✳✳✳ | Certainly neutral, just notched by a venial bright note on the mid high range. Low frequencies very extended and linear. Excellent grain fineness. Harmonic content of good level.

Dynamic: ✳✳✳✳ | High, both in big excursions and in micro contrast; instruments lively and contrasted. There is a light tendency to "pull out" at high volume, typical behavior of high power amplifications.

Velocity: ✳✳✳✳ | Realistic and extended in every frequency range.

Detail: ✳✳✳✳✳ | Very high and always very homogeneous among the frequencies.

Clearness: ✳✳✳✳1/2 | Very high, it consents to listen to every particular with disarming easiness, most of all the background instruments that are sometimes less intelligible in less revelator electronics.

Image: ✳✳✳✳ | Very wide in every dimension, with a credible and solid scenic recreation. At high volume the sound objects are just a bit bigger than required.

Manufacture: ✳✳✳1/2 | Of a good level, with a very first choice in the passive components with respect to the budget. Massive aluminum chassis with enormous heatsinks.

Price/quality ratio: ✳✳✳1/2 | Really good, mostly if referred to the quality obtained for the powers at stake.


Official technical specifications:

Both channels driven from 20hz to 20khz

Power: 310Watts continuous per channel into 8ohms

Frequency Response: 20Hz to 20kHz ±0.2dB, -3dB at 1Hz and -3dB at 70kHz

Distortion: typically <0.05% THD at rated power. 0.1% THD and IM worst case prior to clipping

Current Output: 50A short duration peak per channel, fuse protected

Rise Time: typically 5µs

Phase Response: +0° at 20Hz and -14° at 20kHz

Hum & Noise: 100dB below rated output 20Hz to 20kHz A-weighted

Input Impedance: 47,000 ohms

Gain on RCA Inputs: 32dB

Gain on Balanced Inputs: 38dB

Dimensions: 500x220x455mm, 19.75x8.75x18" (WxHxD)

Weight: 38kg, 83lb

Official Italian dealer: to Il Tempio Esoterico website

Official current price in Italy: 13,490.00 EUR

Associated equipment: to Paolo “Miracle” Di Marcoberardino system