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"Micro Series" Stereo DC Power Amplifier


A peek inside:

Here's the review that appeared in the July 1979 issue of High Fidelity:

A Compact and Very Unconventional Amplifier

An unusual beast, this amplifier.  In the first place, Technics has designed a switching power supply for it to dispense with the traditional bulky transformer that would otherwise tend to swell it beyond its modular-micro format.  In the second place, the company includes a strapping feature to convert the SE-C01's basically stereo circuitry for mono operation—a feature common in public-address and other commercial-application amps but not in home gear.  And both aspects of thd design have some rather surprising ramifications.

The switching power supply leaves some residual of its switching frequencies in the output, which therefore would make unweighted noise measurements (ours are A-weighted) appear poor.  The switching frequency is always about 20 kHz, so it is (at least in theory) inaudible.  The exact frequency changes somewhat, depending on how hard the amp is driven; it showed up anywhere between 21 and 27 kHz in the bench tests at DSL.

The amp gets noticeably warmer than most contemporary power amps, though you should be able to avoid outright misadventure by heeding Technics' warnings about allowing the SE-C01 proper ventilation and keeping it from sources of heat.  There does seem to be current limiting in the design.  Note that maximum output power into a 4-ohm load is a little less—not more—than that into an 8-ohm load, though the actual power level in both cases is above Technics' rating of 40 watts per channel.

When a strapping switch on the bottom of the amp is used to convert it to mono use, more surprises show up.  As it turns out, however, the surprises are occasioned less by actual performance than by Technics' specs—which on paper, make it appear that th mono strapping is almost worthless.  We might assume that the feature was provided so that owners wanting to increase the power of their systems could buy a second amp and use each—strapped—for one channel of the stereo pair.  But Technics' own claim in the mono mode is a mere 1 dB above the per-channel power rating.  Big deal!  On the bench, however, it turns out that clipping power is 2 dB higher into 8 ohms and 5 dB less power before clipping the music-simulating tone bursts of the dynamic headroom measurement  than it does before clipping the steady tones of the regular clipping test; in mono, the dynamic headroom is dB above the steady-state clipping level.  So the per-channel power the amp can deliver into 8-ohn loads is 45 watts stereo and 85 watts mono with sine waves and the equivalent of 40 watts stereo and 90 watts mono with the simulated music!  In other words (and despite the implications of Technics' specs), you can effectively double the power by adding a second amp.

The oddities made us wonder what we would hear when we used the SE-C01 in a listening system.  Not to worry: It sounds just as it should.  While we would not attribute any distinction to it, its sound is as clean and well-defined as that of any regular moderate-power amp (separate or built into a receiver) with which it would occur to us to compare the Technics.  Distortion is very low (and essentially the same in both operation modes) and generally remains low even if we consider the power-supply switching frequency as "distortion".  Checks of intermodulation at high frequencies—which we thought might be aggravated by the switching frequency—were all below 0.075% and dropped to the level of the harmonic distortion measurements by the time the test tones had descended the into the 10 kHz region.

It should be fairly obvious that we don't know quite what to make of this design.  Like all the Technics micros, it is elegantly sharp-edged in style and features gold-plated input contracts and non-scratch feet that can be folded down to tile the amp upward for a better view of its LED power metering.  And somehow the omission of an on/off switch (which Technics assumes will be supplied by your—and preferably their—preamp) lends some special "feel".  But the unconventional behavior of the circuitry is harder to assess.  We liked what we heard, and perhaps that is all that need be said.


This was last updated 1 June 2002.

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