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Amplifier Pioneer A-400 review

And now for something very slightly different – the Pioneer A-400. Yep, it looks just like the A-300 and it even uses the same switches, circuit board, star-earthing pattern, three-core mains lead and casework as the A-300. But closer inspection unveils a succession of detailed revisions, subtle differences which propel the A-400 into a league of its own!

From the outside, only its extra MC input selector hints at any change -another, remotely-controlled switch that engages a discrete, very-low noise headamp. After this comes the active MC/MM RIAA network, very similar to that found in the A-300 but equipped with a superior two-channel op-amp and near-imperceptible differences in the selection of passive components.

Step a little further back and the larger mains transformer pops into view as do the 10,000uF audio-grade reservoir caps, replacing the 6,800uF electrolytics found in the A-300. Of course, the A-300 is rated at a nominal 30W whereas the heavyweight A-400 offers 50W.

Once again, Pioneer’s proprietary ‘SuperLinear Circuit’ topology is used, pitching the non-linearities of one transistor against the opposite but equal non-linearities of the other. Meanwhile, in order to satisfy the demands of a higher output, Pioneer has substituted higher-current Toshiba transistors into the A-400.

Sound Quality

Once again we began by listening via the MM input but now the difference between the ‘300 and ‘400 seemed quite vast, this latter model stripping through the murk that fogged-up the ‘300. This unearthed an explicitly detailed treble, not bright or aggressive but very light, free and bubbling with detail. There was an excellent sense of stereo space, the freedom from compression having everyone tapping their feet within seconds!

Furthermore, this amplifier showed a real command of music and so deep bass growled without clouding midband detail. It was very weighty and enjoyed excellent separation, just as brass had a naturally tangy quality that was raw but not cold or ascerbic. There was certainly not the ‘editorialising’ heard with the ‘300, instead the ‘400 sounded sharp and detailed, honest but captivating. Duff recordings are going to sound, well, duff, just as a good recording will surely shine. After all, accuracy is rarely sympathetic.


Some perspective is definitely required here. Throughout the blind listening tests the Pioneer A-400 emerged as a highly polished performer, though not necessarily as a blatantly obvious ‘winner’. Unaware of its manufacturer or price, it was considered to match the weight and punch of Mission’s Cyrus Two, the exquisite string tone of the Dual CV5600 and flighty transparency of the Harman-Kardon HK6500, all the while enjoying a tangible ‘rightness’ that was all its own. Once informed of its price, the members of the panel voted the A-400 a unanimous best buy.

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