Once we have established a firm base for our turntable, and have it revolving flutter- and wow-free, we need to add an arm and cartridge to decode all those tiny, tiny, grooves filled with musical information. They are in essence dynamic explosions, as pointed out previously: some 30 tons per square inch of energy.
The name ‘tone arm’ is interesting, and in the current form of record replay, the last thing we actually want are ‘tones’ to be added by the arm! Of course the phrase developed in the acoustic gramophone era; the ‘tone arm’ was an integral part of the acoustically-amplifying arm, with a ‘sound box’ on the end, rather than an electric device like a cartridge.
Throughout the 1930s electric ‘pick-ups’ replaced the purely acoustic variety. Playing pressures dropped from pounds to ounces, and a one-piece molded arm (usually plastic or Bakelite) had been fitted with a simple coil in which a steel needle was fitted down the middle of the coil.
After World War II, the English company DECCA Records produced the first true high fidelity system, Full Frequency Range Recording (FFRR) , which used a much more sophisticated pick up design. Hot on the heels of this development were of course the 33 1/3 RPM LP, and singles, spinning at 45.1 RPM. Both of the latter were true ‘microgroove’ (early 78s being ‘coarse groove’) discs.
By the late 1950s, stereophonically-recorded discs added another twist. In a mono disc the stylus only moves in the horizontal plane; in a stereo disc, the stylus moves vertically too, with each side of the groove wall containing the separate channels— hence the 45/45 cut. A stereo disc will be ruined by inappropriate use of a mono pick-up, and the stylus for the ‘new’ stereo discs, was even smaller than the ‘new’ microgroove.
It was common in the 1950s for manufacturers to build and sell a matching arm and pick-up cartridge as a package. DECCA’s classic FFSS (Full Frequency Stereophonic Sound, the successor to FFRR) pick-up system was available with three pick-ups: red for 78s, green for mono microgroove, and white for stereo microgroove. EMI’s stereo pick-up package was similar, as was that of Ortofon. At the more budget end, a deck would come complete with a fitted arm and suitable, usually ‘turn over’ cartridge, with a 78 stylus on one side, and an ‘LP’ stylus on the other.
The tone arm that really broke away from this mold was the classic SME 3009/3012. Rather than fixed geometry, the SME design was ultra flexible, allowing usage of a wide range of cartridges. The arm remained pretty much a reference until the 1970s.
The majority of arms made to today, or through the 1960s use some kind of ball race for horizontal movement, with a fixed pair of bearings for vertical, up and down movements. (REGA, Linn, etc – SME used a ball race, and the famous knife edge bearing). Of course the ball race has to be as smooth as silk, friction-free, and noise-free. Gimbals can be used, and offer a much smoother system than a ball race (the earliest I have in my collection using a gimbal is a LEAK arm and moving coil pick-up, the most recent an Alphason Xenon). Highly underrated in general is the uni-pivot, which can come in ultra low mass, ultra high mass, and even oil damped.
A few other clever systems have been tried. The famous Well Tempered Arm uses a microfiber thread, from which the arm is hung; the arm base ‘damped’ in a large bath of fluid, which provides the mechanical grounding. A recent twist on this tale (no pun intended) is Clearaudio’s magnetic bearing. It is not a true magnetic bearing at all, but similar to the Well Tempered , a strong (this time metal) thread ‘anchors’ the arm to the base, from which it pivots and twists, and an extremely powerful magnet system holds the cable taut, and provides some mechanical damping. Clever, but in my experience, the sonic results aren’t that impressive.
That leaves us the so called ‘holy grail’, the parallel-tracking tone arm. Fantastic idea in theory, the record is played in exactly the same style as the way it was cut, reducing tracking error to a theoretical zero. These designs fall into three distinct categories.
The first popular type was the RABCO. This used a pretty primitive mechanical system, with a small electrical motor being used to propel the arm. As the arm was playing through a record, the arm would move out of true alignment slightly, and a small rubber wheel (I’m simplifying this!) engaged onto a spinning shaft which helped propel the arm base down its linear track. Sticking, jumping, and mechanical noise are quite major issues.
RABCO was wiped out by a more sophisticated electronic European competitor, which further inspired Japanese competition. Bang&Olufsen threw everything in to the Beogram 4000. Industrial design by Jacob Jensen (a personal hero) leaf spring sprung suspension, a fantastic main bearing, and electronics, lots of electronics! The arm featured an electro-optical sensor on the rear of the arm; so there was nothing mechanically touching, a huge improvement on the RABCO. This operated an electronically controlled servo motor to gently pull the arm along. This still generates noise, and the arm still has to go in and out of alignment all the time, but with an ultra light tonearm with one of B&O’s superb moving iron cartridges on the end, it was quite successful. Even if, despite high costs, it could be blown out of the water by much simpler decks at half the money. But what an influence this deck had! Look at Technics range of parallel trackers. They stole the entire concept, even down to the T4P plug in cartridge, a pure rip from B&O. And some of these don’t sound that bad!!
There have been a couple of attempts to make a non powered arm. The Souther and Nottingham Analogue arms had a go; both pretty useless, in my mind. But the models that really gain excitement are the ‘air bearings’. To break friction, something the other arms mentioned in this paragraph totally failed to do, the arm rests on a cushion of compressed air. Air bearing arms are possibly the most recognized sub-set of parallel trackers, but are not without their issues. Air is not the most dense or strong of materials, even if you compress it. Air bearing parallel trackers are more ‘hover arm’ than a firmly-grounded arm, and to my ears, I prefer a more solid connection. Never mind the noise the air pump makes….
Back to more conventional arm designs. Obviously, sticky bearings are going to spoil the party, so nothing but the finest engineering should be utilized, and clearly the arm’s geometry must be spot on, as well . As it is plainly obvious the arm itself will have a tonal and resonant effect on the sound, it should be self-damped as much as possible through shaping and construction. One piece arm and head shell units, such as the Xenon and HR100s designed by Mike Knowles at Alphason design, are one very valid approach to providing self-damping.
Rigidity and strength are also worthy obsessions, but both the overall mass and the “compliance factor” need to be watched. Simply put, the lighter the cartridge mechanism and overall weight, the lighter the arm should be to match it. For record wear the lighter the better. But just to be awkward, the most linear cartridges tend to be heavier moving coils, with large saturating magnets, which tend to offer a better sound.
Luckily, these days most modern arms are quite happy with a reasonable range of cartridges, and most cartridges seem to be around the 6-10 gram in weight mark. Some do get it very wrong; I was amazed at one budget manufacturer who fitted an incredibly lightweight carbon fibre arm, with a moderately heavy cartridge. The result was it jumped on most of my 12” 45s – this is very basic stuff!
I am shocked when I look at some arm designs, as it is clear that a lot of so called ‘experts’ don’t really have that much of a clue. Unlike electronics, there are very few texts about arm design, and most of them are from the 1960s. So it does take a pure mechanical genius to come up with something really new.
0 comments