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by A. Edelstein
----------- Princeton Design Group Active Cartridge Stabilizer
Solid-state cartridge stabilizer. Price: $400 (30-day money back guarantee). MANUFACTURER: Princeton Design Group, P.O. Box 398, Princeton Junction, NJ 08550. (201) 329-6473.
Consider the stylus's difficulty of maintaining constant contact with the groove, which it must to maintain sonic fidelity.
The stylus is bounced about unmercifully on its appointed rounds by the undulating record groove. The wonder is that records work at all, much less reproduce sound as well as they do; bees fly, in spite of some engineers' proofs to the contrary.
Consider the difficulty a car's suspension has keeping the wheels in contact with the road, especially on a bumpy surface. A car's suspension is made up of two elements: the spring, for isolation of the chassis from the road; and the shock absorber (more properly named a damper in the UK), to resist the spring's tendency to oscillate continuously when excited.
In contrast, our beleaguered stylus has only one suspension element, a single piece of rubber which must act as both spring and damper. Compromises in the performance of either function are necessary, particularly the damping function. It would seem that separating the springing and damping functions in a cartridge would lead to better groove tracing, hence greater fidelity.
There have been attempts to separate the two functions, most notably silicon tonearm damping. Well-known examples are the SME trough and the Keith Monks and Decca International- unipivot tone arms, which have received favorable reports in these pages. A second type of more elementary damping is available from Shure in the form of their damped groove brush.
Yet a third form of damping, available from Princeton Design Group, is a more sophisticated way of separating the springing and damping functions of the pickup system. The product is called an "active cartridge stabilizer," which I'll simply refer to as "stabilizer" from now on.
The PDG product is an active electrical device placed in the signal path between cartridge and preamp. This sounds suspiciously like a pre-preamp, and, indeed, it can function in that capacity as well. I used the stabilizer, however, in a unity-gain con figuration to electrically stabilize the mechanical behavior of a moving magnet pickup, which is its unique capability, and my particular interest. My favorite cartridge is the Technics EPC-100MkIV, a moving magnet reviewed very positively by JGH in Vol. 7, No. 6; my observations were made using it, and a Signature 8M at PDG's booth at Chicago CES. It's a funny thing: all along, one of the real advantages of using a moving-magnet rather than moving-coil cartridge has been the elimination of the pre-preamp's extra circuitry, and the consequent economic savings. Now along comes a device to equalize this inequity-we moving magnet fans can finally hold our heads high.
Here's a simplified explanation of how the stabilizer works. Generators and electric motors are electromagnetically similar devices used in different ways. In a generator, a coil of wire is moved in a magnetic field, inducing a voltage in the coil of wire; both moving-magnet and moving-coil cartridges are generators. In a motor, the setup is the same, but electricity is passed through the wire coil, resulting in motion.
The Princeton stabilizer performs its damping function by feeding current back into the cartridge, turning it into a motor. The output of the cartridge is read by the stabilizer, and a current based on this reading is fed back into the cartridge, producing motion opposite to the spurious oscillations of the stylus. (Actually no motion occurs; instead there is resistance to the motion the cartridge is already involved in.) Since the amount of damping is directly related to the output of the cartridge, the Princeton stabilizer performs as an intelligent, electronic stylus damper-a very clever idea.
Each stabilizer must be set up for the cartridge with which it's to be used. The changes are simple, involving the exchange of a few plug-in resistors, but failure to configure the stabilizer correctly can be disastrous. Flat frequency response may well be destroyed, and the gain of the stabilizer can be incorrect for your system.
I learned this lesson the hard way the first time through with my Technics EPC-100MkIV.
Does the Active Cartridge Stabilizer work?
I wouldn't have spend my time on this review if it didn't. It sounds just about the way the design concept implies. The first time I heard it, at the Chicago CES with a Grado Signature 8M, I listened both with and without the stabilizer, and you didn't need a golden ear to appreciate the results. The expected improvement in clarity and definition was immediately evident over the whole sonic spectrum. Individual instruments and voices were more clearly defined; bass was a little less full, but tighter, more defined, and actually had greater dynamic impact. At first I was bothered by the loss of bass quantity; this might indicate a frequency response anomaly. Then I realized that this loss was consistent with the improved damping claimed for the stabilizer. Because of the large stylus motion involved in tracing bass tones, a greater portion of undamped spurious oscillation is in the bass region. There would therefore be more damping in the bass, which would reduce the apparent relative quantity of bass.
Treble was much cleaner, but at the same time brighter, than without the stabilizer.
This is consistent with the lightened frequency balance caused by the tightening of the bass. And, as expected, the midrange was smoother and better defined.
These listening impressions were con firmed when I got a chance to listen to the stabilizer at home with the Technics EPC-100MkIV. Home listening was also more extended and relaxed; I found myself listening at higher levels with the stabilizer than without it, indicating smoother overall response. Spatial characteristics were improved, but "air" was reduced, which sounds almost self-contradictory. I use the term "spatial characteristics" to refer to a sense of three dimensions. "Air" refers to the motion of the air within the soundstage. Increased air sounds exciting, but I worry that it's really a subtle distortion, or smearing; it seems to be reduced every time I substitute what I believe to be a smoother component in my system. I see the danger of circular reasoning here, so I won't be too adamant. I nevertheless feel that the better spatial characteristics and loss of apparent air in the Active Cartridge Stabilizer aren't contradictory facets, but real improvements.
This is a solid-state device (it wouldn't be possible to economically accomplish what the Princeton stabilizer does with tubes), and sounds like a solid-state device, albeit a very good one: smooth and lacking in grain. Audiophiles with good solid-state amplification will probably like the stabilizer. Tube enthusiasts used to the rich, lush, classic tube sound may not be so enthusiastic, but I recommend an audition anyway. Its virtues may put you at odds with your basic audio tastes. Audiophiles with the new, leaner, tighter-sounding tube gear will probably take the middle ground in their responses to the PDG stabilizer.
[1. AE's explanation of components being more accurate.
but seeming to subtract air, makes sense-but his definition of air doesn't, as far as either JGH or I could deter mine. To our (collective) mind, "air" refers to a quality of high frequency extension that makes you think there's no limit to how far out the highs go. The only air you could hear moving within any soundstage would be wind. Occasionally you get wind at the opera here in Santa Fe, which is outdoors, but not in most performing sites—LA]
This is a whole new type of device for moving magnet aficionados, one that owners of top-quality MM cartridges-Shure VI5 VMR, Grado Signatures, Technics EPC100 and EPC205, and others-will certainly find intriguing. Moving-coil users shouldn't forget that the Princeton stabilizer can be set up as a pre-preamp as well as a damping device, and deserves a listen in that configuration.
All in all, this is a unique and fascinating high-performance product. If you value bringing out all the detail there is on a record, you would be cheating yourself by not giving it an audition.
--
[based on a Feb. 1986, Stereophile review article]
Also see:
ANOTHER VIEW OF THE PDG--WITH THE DYNAVECTOR PE-2 "PHONO ENHANCER" THROWN IN
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