Points Of Pickup

Points Of Pickup

Written by Haden Boardman

The point of contact between the cartridge’s generator system and the actual moving vinyl record is of course the stylus, mounted on to the cantilever. The stylus has to cope with the enormous forces thrust upon it, and stay tracking the groove. Just like every other part of a record playing system, it will impart its own mechanical vibrations and resonances upon the sound vibrations passing through it. Keeping the stylus mass small helps reduce record wear and increase fidelity.

It is not just the size, but the shape and the finish which matter. All styli are amazing works of art; the skill in making and mounting the most basic shapes is immense, and some of the more complex profiles are mind boggling.

A simple ‘spherical’ tip is somewhat frowned upon in High End circles, but if small enough and well polished, they are perfectly valid stylus types. The natural progression from a ‘spherical’ tip, is to carefully polish two sides, and make it more elliptical; usually to a ratio of 1:1.5. Lower priced ‘ellipses’ may well have a lower ratio; more expensive, a higher ratio. Even more expensive and more difficult to manufacture are the ‘line contact’; the diamond is now machined to form very sharp edges, much finer than either the spherical or elliptical types. Different manufacturers give all these quite fancy names, but the premise remains the same, a very small contact area with the vinyl record.  The most famous development of this type is worth mentioning, this was by a chap called ‘Shibata’ in Japan, it was developed to extend playback bandwidth enough resolve the 45 KHz signal required on Quadraphonic CD 4 four channel discrete records.  This wide bandwidth cannot harm stereophonic replay, either.

The last type of stylus profile was developed by the famous Dutch firm of Van den Hul: Under analysis, they concluded the best stylus profile to replay records with was one very similar to the record cutter itself, with refinements so it didn’t damage your precious records on play back. There are of course variants, and competitors such as Fritz Gyger, Paratrace, MicroLine, etc.

A ‘spherical’ stylus type has minimum contact with the groove. The more you progress through elliptical and fine line through to Shibata, the stylus sits very snug in the records groove, with the whole edge of the stylus in contact with the record groove wall.

As mentioned earlier, the stylus is mounted on to the cantilever, which transmits all of the vibrations/musical information in to the main body of the cartridge. The cantilever needs to be ultra rigid, and ultra light, most commonly it is a thin-wall metal tube, but sapphire, carbon, and other exotic materials have been used. Mounting the stylus tip is no easy thing. More budget designs simply ‘glue’ the tip in place, whereas more expensive types use ‘clasps’ not dissimilar to those used on a diamond wedding ring. Somewhere in between,  the end of the cantilever tube is formed in to a ‘flat’ and the stylus tip pierced through. It is obvious alignment is critical – and with all these microscopic procedures you can begin to appreciate why some styli and cartridges cost as much as they do!

Cartridge generators, the parts that turn the mechanical energy in to an electrical signal, are no less complicated and varied. The four main types of generator system are crystal (which are not really hifi – I am wasting no time on these) moving magnet, moving coil, and moving iron.  Moving magnet, or MM, is possibly the most common type. At one end of the cantilever is the stylus, at the other a tiny tiny magnet(s). The vibrations wiggle the magnet in front of (usually) four small coils. These four coils can be a ‘reasonable’ size and are reasonably sensitive, producing a fairly healthy output in millivolts (usually quoted between 3 and 7 mv). The coils are wired in a ‘sum and difference’ arrangement, which translate the up and down and side to side movements in to distinct left and right audio channels. For more information, check out Alan Blumlein’s classic 1930s patent and text on stereophonic sound. MM cartridges tend to be quite light and compact, and are what is classed as high compliant cartridges. They suit lower to medium mass arms.

Moving coil ( MC) switch this around: the magnet is fixed, and the coil is attached to the end of the cantilever. The coils need to be microscopically tiny; to remain low mass enough  to track a record correctly, may be only 25 turns of wire used per winding. Different armature designs vary from a cross shaped device (like an ‘X’), to winding directly in the cantilever. In most MC cartridges a fairly substantial (heavy!) magnet is fitted. This gives the advantage over a MM cartridge of saturating the coils with magnetic flux, which makes for a very linear response.

MC of course have their problems. Those coils need connecting to the back of the cartridge pins with micro fine wire (usually a continuation of the coil itself) and those tiny tiny coils are only capable of generating very very tiny outputs in micro volts, some as low as 100 uV. This places demands on the amplifier chain, and requires nothing but the finest arm cables to connect it. Moving coils weight quite a bit too. The heavier the magnet, the more linear the performance – but the higher the mass. The smaller the coil, the more linear the performance, but the lower the output.  High output moving coils exist: they literally have much larger coils, compromise exists here.

Easier for the electronics to be more linear, but a slightly less linear cartridge. Ortofon patented the stereo moving coil cartridge back in 1961. It, again, was pretty much identical to Blumlein! But through the 1960s and 1970s, you either paid Ortofon to use their patent, didn’t bother, or came up with something else. Audio Technica  came up with something else: their cartridges are based on a record cutter in reverse. With just two coils ‘on top’ of the cantilever. The current en vogue Neumann  DST uses a similar system too, but with the coils virtually ‘sat on top’ of the stylus- certainly gets around some cantilever problems!  But post-1983, when Ortofon’s patent run out, it was a free for all. And most manufacturers use a generator system pretty similar to this classic design.

London DECCA produced the most successful moving iron pick-ups. Again, there isn’t much of a cantilever, in fact there isn’t one! A ‘T’ shaped armature has the stylus at its base, and the iron inductors are placed within a set of coils above and below the iron inductor (a magnet sits on top of the entire structure). In a conventional stylus a cantilever has a critical ‘pivot point’ between the stylus and the generating system – some manufactures go for a very short cantilever, others a long one. The DECCA has none. There can be no doubt the powerful sound this gives. But it is very unkind to record, and record wear is somewhat enhanced compared to more standard methods.

There are of course variants on these themes. B&O moving micro cross (in recent years revived by Soundsmith), Technics HPC, Grado, plus some outright oddities: STAX electrostatic (more electrets!) ribbon, strain-gauge, optical….

As you can see, there are very many variables in cartridge design. Is a MM cart with a line contact stylus better than a moving coil with a spherical tip? Answers on a post card, although yours truly has always been more of a ‘coil fan! It must also be remember the smaller the stylus tip, the smaller it moves in the groove, and the smaller its output. The lower the output, the better your electronics better be!

The most important thing to consider is arm compatibility. A high mass cartridge (low compliance) needs a high mass arm; otherwise it will distort and mistrack. A low mass, high compliance cartridge will likely be ‘bottomed out’ by an arm too high mass. Sadly even manufacturers get this wrong. And with all these variables, you can see why! Once you have the right arm, its vital to align it with the record groove correctly. Not just the tracking error, but also the vertical tracking angle, or VTA. A spherical stylus is quite unfussy about this in comparison to a Shibata, which is critical. Failure to set this right will mean a very expensive Shibata will mistrack, and sound much worse than styli a quarter of its price.

Whoever said record players are easy?

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