Decca Mark V phono cartridge

The Decca Mark V is the latest version of that English firm's unique "tip-sensing" stereo-matrix-ing pickups. The "matrixing" apellation refers to the fact that the Decca pickups do not use 45°–45° sensing coils, but use instead a combination of vertical and lateral-sensing coils. There is a single coil for lateral sensing, with its pole pieces brought down next to the tip. This is the tip-sensing feature, whose major attribute is that the stylus motions don't have to be conveyed along the length of an armature before reaching the transducing pole pieces. Thus there is virtually no possibility of the stylus vibrations being modified through flexing of the armature prior to their transduction into audio signals.

Then there are two vertical-sensing coils with pole pieces located directly above the top of the armature (fig.1). These are not tip-sensing, but since the armature is a straight, vertical rod, the only thing that could modify tip vibrations on the way to the pole piece is longitudinal compression of the rod, which is likely to be of negligible magnitude.


It is important to note though that, while the lateral sensing arrangement is push-pull (the stylus approaches one pole piece as it leaves the other), the vertical sensing is single-ended (becoming more sensitive as the stylus lifts up towards the polepiece). In theory at least, this must cause more waveform distortion from vertical modulations than from lateral ones. More about this later.

One end of the lateral coil is connected internally to the connection between the two vertical coils, with the latter connected in opposite electrical polarity. And here's what happens:

Whenever the stylus traces a 45° stereo modulation, representing one channel of recorded information, it moves both laterally and vertically (fig.2). Sensing takes place in both the lateral and vertical coils, but since the vertical ones are out-of-phase, only one will match the polarity of the signal from the lateral coil and produce output. The other will cancel the lateral-coil signal, producing no output. Result: stereo separation.


As the groove angle changes from 45° for a change in stereo direction, vertical-lateral cancellation will increase in one channel and decrease in the other, and the relative signal-output levels will change accordingly and appropriately.

Lateral groove modulations (mono, or center-stage stereo) will produce sensing in the lateral coil only. The vertical coils won't respond, so no cancellation will take place. Vertical modulations (rear ambience or, when mixed with lateral, stereo difference signal) will produce equal out-of phase signals. The lateral coil won't respond, so no cancellation will take place.

An odd way to play stereo discs? Not really. All London discs, and many other European ones, are made with cutterheads that use the same matrixing principle only in reverse.

How then does the Mark V do as a reproducer? That is a moot point, for the English Decca firm (footnote 1) has such sloppy quality control that it is said, with justification, that there's no such thing as The Decca Mark V; there are a number of them, all different, and ranging in performance from excellent to execrable.

At least one of the US importers (Paoli Hi-Fi) pretests every Mark V received, and packs the machine-run frequency-response-and-separation curves with each Export model that passes muster. As a consequence, outright duds aren't likely to reach the consumer, but there are nonetheless still some measurable variations between one sample and another.

The curves in fig.3 show what can be expected from a typical Export Mark V (curve 1) and a typical standard Mark V (curve 2). Curve 3 is what can, if you're lucky, be found in an occasional Export model and in a rare standard Mark V.


The curves don't tell the whole story, though. High-end smoothness is high-end smoothness no matter how you interpret it, and the smoother the highs, the better the sound. But, there's something else that affects the Mark V's sound, and which has no effect on its frequency response, and that is the distance between its armature and its single-ended vertical-transducing polepieces. The distance which yields maximum lateral/vertical cancellation (ie, the widest separation) may not yield the lowest distortion. Thus, there is an inverse relationship between measured separation and the listenability of the Decca pickup. Samples which have less than the 20dB+ midband separation of a typical Mark V tend to sound sweeter and more musical, yet there is no audible impairment of stereo spread until separation (in the 3kHz range) falls to around 15dB, which happens to be the reject point for Paoli Hi-Fi's Export models.

Choosing a Good One
So, that suggests how you can select the best-sounding Export Mk V from a dealer's stock (if he'll cooperate). pull about half a dozen Export boxes from his stock (more, if he'll sit still for it) and peruse the response and separation curves of each one. Choose the one with the smoothest high-end response and the separation closest to 18dB at 3kHz.

If you're buying a standard Mark V, or an Export model from a distributor that doesn't include curves, picking the best of a batch is a bit more difficult but not much. There are two ways of going about it: The needle-talk test and the usual listening test. It's preferable to use both.

First, obtain a disc with some loud, shrill massed-violin passages on it. (Any recent Columbia, New-York Philharmonic recording should do fine.) Take the disc to your friendly hi-fi dealer and ask if you can try out a number of his Deccas. But use your head about this; if you ask for that favor when he has a store full of customers, you should not expect (and probably won't get) cooperation. Schedule your auditioning session in advance, for a time when you'll have the store to yourself.

Snap each cartridge in turn into the arm, turn the system's volume all the way down, play one of the shrill sections on your disc, and listen to the needle talk coming directly from the cartridge. Pick the one with the least, and the smoothest-sounding, needle talk

Then listen to it through the dealer's system, comparing it with some of the samples you rejected. Yours should sound the least brilliant of the bunch. It's a sad commentary on Decca's quality control, though, that an occasional standard Mark V (the "cheap" $109.50 version) will sound, and measure, better than typical samples of the $135 Export model.

Sound Quality
In truth, most current stereo pickups could well do with some of the extra hardness that is audible from some samples of the Mark V, for the majority of them have a rather dark, dull sound to begin with. The Mark V's strongest point, though, is that a good one has just the right amount of brilliance to make a disc sound almost exactly like its master tape, so any additional brilliance as a result of distortion can be too much of a good thing.

It isn't brilliance alone that sets the Decca apart from its competition, though. The pickup also yields the clearest, most highly-delineated sound of any stereo pickup we know of, and has a limpid transparency that was equalled only by the old Weathers monophonic FM pickup (which also used tip sensing!).

That quality of delineation is hard to describe, inasmuch as we hear it in live music as well as in some (not all) master tapes. But dauntlessly, we will attempt to desscribe it anyway. If you can visualize an audio signal as a series of impulses with sharp dips between them, and then mentally blunt the bottoms of the dips, you'll have an idea of what the Decca does not do that all other pickups (to date) do (fig.4). How the Mk V's superior detail sounded to us (top) in comparison with that of the Shure V15-III and Ortofon M15 Super.


To quote one observer, the Decca's sound seems to have "air" around it.

Along with this airiness, and possibly also attributable to the tip-sensing feature, are a remarkable quality of front-to-back perspective (depth) and of imaging stability. The sound is not quite as vastly spacious as that from, say, the Shure V15-III, but the Decca seems better able to maintain full separation and directional specificity at high modulation levels, despite the slightly superior measured separation of the Shure.

Some listeners, unimpressed with the way the Decca's "aliveness" can so easily become hardness, have raised the question of the pickup's electrical distortion, pointing with suspicion at the single-ended vertical sensors. We must acknowledge that possibility, as there is certainly nothing about the Mark V's frequency response that would explain why it has that tendency toward brightness.

Footnote 1: Once a division of the Decca Record Company (of Decca, Deram, London, ffrr, ffss, and not-signing-the-Beatles fame), the Special Products Division became an orphan when the record label was absorbed by PolyGram in the late 1970s.—John Atkinson