Benefits from bolts that are just nuts!
By Roy Gregory
Bolting a phono cartridge into a tonearm headshell might seem like the most basic of mechanical tasks, but like everything else in audio there are subtleties to consider beyond the obvious. Yes, you want a positive mechanical interface and yes, you want the fixing to be easy to use – hence the choice of allen heads over slotted screws – but there are other considerations…
Cartridges are micro generators, involving waggling a coil of wire in a magnetic field (or vice versa). The fixing bolts in any cartridge sandwich that magnetic field on either side and, if they are themselves magnetic, they exert a direct influence on performance by altering the relationship between the wire and the magnetic field. So fixings should be non-magnetic – and many aren’t. Non-magnetic stainless steel is perhaps the obvious choice. The problem is that despite many peoples’ assumptions, not all stainless steel is non-magnetic. In fact, the majority of stainless alloys exhibit varying degrees of magnetism. It is only Austenitic stainless steel, with its higher proportions of chromium and nickel that is genuinely non-magnetic. So simply using ‘stainless steel’ isn’t enough.
Then there’s the question of mass. Cartridge/tonearm resonance is a critical factor in phono performance. It depends on the weight and compliance of the cartridge and the effective mass of the tonearm. But in calculating the weight of the cartridge you must add the weight of any fixings (nuts, bolts and washers). That’s why, back in the day, SME supplied nylon mounting bolts with its super low-mass Model III/IIIS tonearms. After all, why make a super-light tonearm and then hang lumps of steel on the end of it?
Finally – and from a rather more esoteric perspective – there is the ‘sound’ of the fixings themselves. Although the idea that certain materials impart a signature to sound is anathema to the measurement brigade who demand scientific explanations for everything (while ignoring the fact that ‘science’ only explains what we can, not what we can’t) there is a considerably body of work/opinion within the audio field as to the musical merits of various materials. In certain cases this influence can certainly be demonstrated, even if it can’t be fully explained.
Most cartridge mounting hardware uses an M2.5 thread. There are exceptions, such as the Goldbug Briar cartridges, but they are increasingly rare. Over the years, other cartridge manufacturers have supplied specific mounting hardware made from a ‘preferred’ material, such as brass or aluminium, chosen for its non-magnetic qualities. The problem is that even if those fixings are mechanically sound and reliable (questionable in the case of aluminium) then all too often they fall foul of their sonic characteristics. Despite its widespread use in connectors, an increasing number of audiophiles are questioning the character imparted by brass parts.
It’s all about access…
Back when I started in hi-fi retail, getting decent cartridge mounting bolts meant a trip to Clerkenwell Screws in the City of London, one of those wonderful old specialist shops with a dusty window, a narrow counter and a stock room that stretched back like the final resting place of the Ark in Raiders… The staff at Clerkenwell Screws, clad in their brown shop coats, could dig out almost anything, just so long as it had a thread. These days, thanks to the dubious wonders of eBay, any member of the public can access esoteric fixings with nothing more than a few clicks of their mouse. You want M2.5 stainless-steel allen bolts in almost any reasonable length? Not a problem. But why stop at stainless-steel, when other, potentially superior options exist.
