AudioQuest 7000 Fe5 MC phono cartridge Page 2
The stylus profile is not as radical as that of a MicroRidge tip, but it is "friendlier," Carr told me, to set-up inaccuracies and won't chew up records. In fact, I found that with both cartridges, the tip contacted virgin areas of the groove, thus reducing wear noise on many of my older records—a definite plus.
Both tips dug dirt from record grooves I thought were clean, a minus. For some reason, the Clavis was more prone to sludge build-up than the Fe5, though I have no explanation as to why. The solution, of course, is to play cleaner records; neither of these cartridges, nor any other premium priced unit, should be used with dirty records. In fact dirty records shouldn't be played with any cartridge!
In the general model, the cartidge cantilever is bonded to an aluminum pipe which is fitted with a brass or aluminum end piece with a small hole drilled into its center. A tiny piece of wire is passed through the hole and crimped on the other side in the space between it and the end of the cantilever, thus locking it in place.
The wire can be any kind of spring material: piano wire, beryllium/copper, phosphate/bronze (like a guitar string). It can be solid or stranded. Solid wire tends to be more springy, stranded more compliant. In the original Dynavector Ruby—a classic hi-tech cartridge of the late '70s/early '80s—a piece of nylon was used instead of wire. The material used in this critical part of the design affects both the compliance of the cartridge and its final sound. This is, as Carr told me "a designer's choice."
The ultra-thin wire is then threaded through a tiny hole in the all-important core/coil combination, which then mounts flush with the back of the aluminum pipe. The wire is threaded through another pipe, called the "stopper pipe" by Scan-Tech, and then it's crimped on the other end.
There is a space between the two pipes where the wire is free to flex. That, believe it or not, is the pivot point around which the whole shebang moves. Thus, when you lower the stylus into the groove and you see the cantilever "give," it is the wire which is flexing. In order for this single-point suspension system to work optimally, the stopper pipe must not allowed to move.
The core itself can either be square, as it is in the Scan-Tech designs (two millimeters square), or it can be an X, a cross, or even a V shape. The X shape can offer somewhat greater channel separation, but because there is less core material, the cartridge has a lower electrical output. Again, this is a design choice: the highly regarded Benz line uses the X core, for example.
The core can be iron, or carbon fiber, or other materials. According to Carr, the Clavis DC's core is gold-plated "five nines" (99.999%) chemically pure iron. The Fe5's core is also fabricated from "five nines" iron (thus the Fe5 name), but Low did not say whether it was gold-plated.
A pair of crossed wire coils are wound around the square cores on both Scan-Tech designs: the Clavis uses "six nines," high-purity, stress-free copper; the Fe5 long-grain, "five nines" "FPS" (Functionally Perfect Silver). Again, these are designer choices based on listening.
The cantilever/core/coil subassembly is fitted through a cone-shaped hole drilled in the pole-piece, a hole you can see when you look down the barrel of the cantilever of most cartridges. Usually, there is also a hole drilled into the rear pole piece, into which the stopper pipe fits. Yet another hole is drilled into the rear pole-piece, but at a 45° angle to the first hole. This one is tapped for a set screw, which is used to firmly anchor the stopper pipe.
Consider the miniature size of all of this, and the precision with which it all must be machined and assembled. and you begin to appreciate the difficulties involved in cartridge manufacture.
The space between the core and the rear pole-piece is where disc-shaped rubber dampers are fitted, threaded over the stopper pipe before it's inserted into the rear pole-piece. Usually there's a large damper to control bass frequencies, and smaller ones to deal with high-frequency resonances. The wire is the suspension "spring," the dampers are the "shock absorbers" of the system.
Whether butyl rubber, silicone rubber, or just plain natural rubber is used as the damper is a design choice which, according to Carr, probably has the "single biggest effect on the final sound—that and the cantilever material itself."
The pinch test
This rubber material is what analog devotees are talking about when they say the "suspension" has dried up and a cartridge no longer sounds good. How long it takes for that to happen depends on the material used, and the smog/ozone condition where the cartridge is used. According to Carr, pure organic rubber can last longer than carbon-impregnated rubber, where the additives can attack the rubber from within.
One way to illustrate graphically what happens to the rubber as it ages is to do "the pinch test" on the back of your own hand. Grab the skin in the middle of the back of your hand with the thumb and index finger of your other hand. Pull up and then let go. If you're in your twenties or even thirties, your skin's "settling time" is probably instantaneous. The older you get, the longer it takes for your skin to snap back, and the longer you'll be able to see the ridge of skin you've pinched.
With proper care, your stylus may very well outlast your suspension, though Carr says that if the designer knows what he's doing, you won't have a suspension "time bomb." Speaking of which, now that you have a feel for what makes the cantilever "give," you can understand why it is so critical to lower the stylus into the groove gently. If you drop it repeatedly with force, you'll flex the thin wire suspension beyond its elastic limit and your cartridge may "bottom out."
Cantilevers and dampers
According to Carr, boron tends to have an easier-to-control resonant signature than Ceralloy, so on the AudioQuest Fe5 just the two sets of dampers previously described are used. On the Clavis DC, an additional rubber "donut" fits over the entire core/damper assembly—an Ortofon innovation (used originally on its MC-20) which Scan-Tech uses with permission.
Pole-pieces and magnets
The magnet sandwiched between the cartridge pole-pieces can be samarium/cobalt, neodymium (the "n" in nsx), or some more mundane magnetic material. Its shape and size can also vary.
The purpose of the pole-pieces is to transfer the magnetic flux from the magnet to the gap in a focused fashion, while preventing stray magnetic fields from reaching the coils directly. A short pole-piece results in a greater amount of magnetic energy reaching the gap (thus greater efficiency), which is good. Unfortunately, it also increases the likelihood of stray energy reaching the gap, which is not good because it increases distortion. The inverse is also true; thus, the designer has to find the ideal balance of magnetic strength and distance from the magnet to the gap.