Three New Step-Up Devices for Moving-Coil Cartridges (Vol.2, No.1: 1979)

Three New Step-Up Devices for Moving-Coil Cartridges: Audio Standards MX-10A; Fidelity Research FRT-5; Marcof PPA-1.

Two more pre-preamplifiers and a transformer assault the gates of SOTA and don't quite make it, but the cheapest of them is an awfully, awfully good buy.

The only way to rate a moving-coil pre preamplifier or transformer is to connect the best possible MC cartridge to it and listen; bench tests don't tell the whole story, as we've had occasion to explain in the past. We gave these units an extremely thorough wringing out in the laboratory, but it was the Fidelity Research FR-1 Mk 3F cartridge and, especially, the Koetsu that showed us what was really going on. Black-box electronic tests (and what could be a simpler black box than a pre preamp?) are still in their infancy when it comes to audio; anyone who tries to tell you other wise hasn't done much listening of the right sort.

The system into which each of these units was inserted for A-B testing was our Reference A (see the updates in this issue); levels were quite carefully matched. Since we know that our conclusions will be upsetting to a number of people, we want to emphasize in advance that our confidence in the validity of these listening tests is particularly high; duplication of our results, however, is possible only with the most meticulous alignment of lateral and vertical tracking geometry, and with a reference speaker that doesn't slow down transients or create significant time dispersion.

Audio Standards MX-10A

Audio Standards Corporation (Division of Duntech Industries, Inc.), PO Drawer 2529, 302 S. Melendres, Las Cruces, NM 88001.

MX-104 moving-coil pre-preamplifier, $350. Five-year warranty. Tested #190, on loan from manufacturer.

This is a tough one. On the laboratory bench, with test signals of all descriptions going in and CRT displays and/or meter readings coming out, the MX-10A is closer to “a straight wire with gain” than anything we've ever en countered in the world of audio electronics. Its grounded-gate FET circuit, derived from RF technology (the discipline its makers come from), is mind-bogglingly wideband, fast and linear; no electronic test we could throw at it gave results even a small notch below perfection. In desperation we attempted to zap it with deliberately vicious and unreal-world complex waveforms out of a new synthesizer we have that can generate just about any signal you can draw with a pencil, and the output of the pre preamp remained literally indistinguishable from the input. Incredible! And yet-the MX-10A just isn't the best MC step-up device known to us. Even the $120 Marcof PPA-1 sounds better in some ways, and the Cotter MK-2 transformer in every way. Not that the Audio Standards isn't an extremely high-quality unit. It's beautifully made, and a few years ago its sound would have been considered a small miracle- it's that good. But today our expectations are higher and our criteria unforgiving.

The comparison with the $495 Cotter MK-2 transformer (standard P strapping) is fascinating. The approximately 80-kHz band width of the transformer appears severely limited next to that of the MX-10A, which is a 2-Hz-to-VHF type of device; the transformer also has measurable ringing up there just before it drops, plus all kinds of other out of-band characteristics that are numerically inferior by a wide margin to those of the pre preamp. About the only electrical spec that doesn't leave the MK-2 mercilessly stomped is equivalent input noise resistance, where the laws of nature are in the transformer's favor.

But when it comes to music, the Audio Standards has a distinctly thicker, denser quality, with considerably poorer delineation of subtleties. The Cotter sounds better focused, more finely etched and detailed, airier, more buoyant in dynamics. A spiccato violin passage, for example, sounds like the real thing through the Cotter and like very good hi-fi through the Audio Standards.

Now why should this be? Obviously, out of-band performance is irrelevant, unless its defects are such that they affect in-band performance deleteriously, which doesn't appear to be the case with the Cotter transformer. It would also seem that the two-dimensional displays of the lab bench don't possess the holistic resolving ability of the human hearing apparatus, at least not when it comes to ultimate sonic subtleties. (See also the seminar transcript in this issue.) It's possible that there are highly elusive propagation and/or field effects in the pre-preamp which are avoided in a completely passive and symmetrical device like the transformer. Damned if we know. All we can tell you is what we measured and what we heard. We can't even point a finger at feed back as the possible culprit, since the MX-10A has no inverse feedback loop.

Isn't it nice, though, that we've come to this kind of impasse instead of having to worry about hum, hiss, cross talk, loads of TIM, etc., as we used to not so long ago?

Fidelity Research FRT-5

Fidelity Research of America, PO Box 5242, Ventura, CA 93003. Model FRT-5 toroidal step-up transformer, $455. Tested #026078, on loan from distributor.

Designed expressly for the new FR-7 moving-coil pickup (reviewed elsewhere in this issue) but specified as suitable for any MC cartridge with an impedance between 3 and 10 ohms, this expensive transformer is rather a disappointment. Compared to the Cotter MK-2, it has severely limited frequency response, especially on the bottom end but also on top, and quite high distortion.

On music, the FRT-5 sounds peculiarly thick and somewhat unpleasant. It gives a definite feeling of information displacement and/or loss. We don't want to belabor the point, since FR is one of the more “with-it” outfits in nearly all matters phonographic, but this just won't satisfy the audio purist.

That said, it matters very little that the FRT-5 provides switching facilities for three tone arms plus a straight-wire bypass around the transformer. On first things it isn't first.

Marcof PPA-1

Marcof Electronics, 7509 Big Bend Boulevard, Webster Groves, MO 63119. PPA-1 moving-coil pre-preamplifier, $119.95. Two-year warranty. Tested #1397100132, owned by The Audio Critic.

This is wonderful news: a $120 MC pre preamp that's quite acceptable even to the ultra-purist with the highest standards. Yes, in an A-B comparison with the Cotter trans former, the top end of the Marcof comes off as a wee bit zingy and its bass a little pudgy.

The pre-preamp is also somewhat noisier, by definition. But its overall sound is extremely clean, open and well balanced, leaving relatively little to be desired. For example, the Audio Standards MX-10A is decidedly less trans parent, even if slightly sweeter and smoother- for three times as much money. The Marcof has all the earmarks of a giant killer.

Our laboratory measurements revealed no faults worth discussing, although the Marcof isn't nearly as wideband, fast and straight-wire like as the Audio Standards. Who cares? In its very adequate passband it stays out of trouble just as successfully, maybe more so.

There's a small penalty of inconvenience to be paid for all this value. The PPA-1 is battery-operated; you have to turn it on and off like a flashlight. The batteries won't last as long as the AC from your wall outlet, and there's a big on/off transient you should guard against by having your preamp volume control turned all the way down. We have no other negatives to report.

Until further notice, then, the Marcof PPA-1 is our Reference B step-up device for MC cartridges. Just in time, too; the Cotter transformer has become much too expensive for anything but Reference A.

Recommendations

As we still believe in the overwhelming superiority of properly designed moving-coil cartridges over ordinary magnetics, these MC step-up devices aren't just accessories but essential links in the chain of our recommended components.

Best way to play moving-coil cartridges, regardless of total cost: Cotter MK-2 trans former.

Best MC step-up device per dollar: Marcof PPA-1 pre-preamp.

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[adapted from TAC]

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Also see:

More and Better Preamplifiers (Again and Again)

Various audio and high-fidelity magazines