By linear amplifier standards, this PWM design will take some accommodating. It’s rather flat, with a dynamically inconsistent sound quality. Not unlikeable, but neither is this an audiophile design in our view
All the practicality of a PWM switch-mode output stage
Has plenty of power and a well balanced sound
Loudness control cannot be bypassed, though it can be set to ‘flat’
Luckily the tone controls don’t fall in this trap
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Of conventional proportions, the Power Plant is not as slim or as button bound as most T+A components and is a little friendlier too, thanks to its smoothly rounded edges. Internally, the main feature of note is the use of a switch-mode PWM output stage, apparently of some sophistication and of proprietary design. The output stage is based on the ‘valve-based’ design of the power amplifiers in T+A’s TCI active loudspeakers.
In T+A’s own words, "the preamp section of the power plant has the same circuit as the R-series preamp P1230R and the PA1230/1530 integrated amps."
According to the literature, it also has a high- quality four fold ALPS motorised potentiometer for volume control and – as with all its amps – hermetically sealed gold contact relays. "The power amp section does not use integrated 'off-the-shelf' IC-amps or the widely used B&O ICE-power based modules. The amp consists of a PWM modulator built around an Analog Devices AD 829 op-amp. PWM output signals drive the current (up to 50 Amps) output section which is equipped with latest generation high-speed IRFB4020MOSFETs.
The power supply is an analogue design based on a big-shielded high power torroidal transformer, with high capacity low impedance smoothing capacitors".
T+A goes on to say that the switch-mode output stages generate the output signal as a large number of very short positive and negative signals. "Our new switch-mode output stages have been developed entirely in-house and include output stages of discrete construction, equipped with the latest, ultra-fast MOSFET transistors and high-power intelligent driver modules. The modulator is analogue, although the output stages feature analogue feedback circuitry designed to compensate for the effects of voltage fluctuations in the mains section, as eliminating the power supply induced signal distortion is otherwise unavoidable."
T+A claims that this is not universal in switch-mode designs, however, the level of feedback is relatively low and is frequency-dependent, being more pronounced in the bass range where high currents flow and diminishing higher up the frequency band. The result is said to be a highly controlled, harmonious sound image which never tends towards harshness, with well defined and perfectly contoured bass. "The enormously lively nature and musicality of this concept is unique. If correctly designed, digital output stages can sound superb as well as generating enormous power, with significantly reduced losses and low levels of waste heat." As input impedance of the amp is a lowish 20k ohms, it’s advisable to avoid high impedance sources.
The Power Plant is equipped with a bypassable tone control stage, though the loudness stage cannot be entirely removed from the circuit. It comes as standard with an infra red receiver, but no remote control is supplied. If you happen to end up with a matching CD player or music player, the remote control supplied with it will also control the Power Plant. As an alternative, you can buy a remote control handset for use with the Power Plant as an accessory.
Listening to the Power Plant is, at times, a dispiriting experience and it quicky becomes apparent that it provides new and, for those weaned on traditional analogue amplification, a rather different set of priorities. Unfamiliar priorities, which cast musical values in a slightly different perspective. This reviewer yields to few, in respect for and liking of T+A’s previous products and for the innovative nature of many of them. But there is little beyond the clearly excellent engineering on what is, after all, a mainstream price amplifier.
The mental picture we developed of the T+A, apart from the fact that it is an attractive package, is that it’s easy to control and has plenty of power on tap. An amplifier with its own personality, that’s subtley different from all the other amplifiers that we’ve tested. Driving a pair of MartinLogan Source electrostatic hybrids is a frustrating experience, with a sound that initially seems to be slightly unsettled, lacking in air and dynamics and with what is best described as a distinctly wooden feel.
But it is also apparent that sound quality varied alarmingly with different sources, speakers and cables and there were indications that the quality of the source disc player was reproduced through the speakers in a rather unfamiliar way. Luckily, the tone controls can be bypassed, which is just as well as this amp is far from transparent.
Using Denon’s high-end DCD-SA1 SACD player, a recording on CD of Mozart’s Piano concertos 212/23 (Andras Schiff, Sandor Vegh, Camerata Academica des Mozarteums Salzburg) sounded unexpectedly mechanical and coarse-set, lacking in expression and life and with complex passages sounding smeared.
Switching to an SACD recording of Bruckner’s 6th Symphony (Gunter Wand/Berlin Philharmonic), the woodenness evaporated and the results were generally better, though this was not always the case when using lesser SACD players (in one instance, an old universal player from Pioneer which sounded uncomfortable with the same range of discs).
Again, the expected air and grace and the sense of being there, was muted. More correctly, simple recordings of single instruments or voices (a recently disinterred copy of Suzanne Vega’s Solitude Standing) sounded close to compelling, with strong presence and capella, but the same qualities were not retained when the music became more densely scored and complex.
Here the music sound hardened and lost impetus, sounding more like a compact disc, Perhaps it is users of this kind of hardware who would be most attracted to what this amplifier has on offer, but for this listener, the Power Plant just doesn’t have the expressiveness, subtlety and resolving ability and the good audio manners necessary to make the grade.
Above all, this is a well engineered amplifier and it is certainly well specified. It is true to the brand’s innovative approach to engineering. Flexibility is also assured by the ability to add MM or MC stepups internally, with adjustable loading parameters and the ability to be reprogrammed by software updates. But, we are not convinced by this example of PWM-based amplification and this applies, to a greater or lesser extent, to most (but not quite all) of the switch-mode amplifiers this reviewer has been exposed to in recent months.
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