What considerations apply to material selection for cartridge mounting bolts?
I have found myself needing some longer bolts to relocate a Shure V15 Type 3 cartridge to a Holbo air-bearing system.
The Holbo tone-arm is a tangential tracker with a rigid rectangular 'launch pad' for the cartridge. The pad is 3-mm thick which is much more than the fixed SME head-shell my dad bolted the Shure to some 45 years ago. If it was supplied with longer bolts, they disappeared decades ago!
I will most likely have a similar issue with my Audio Technica VM540ML cartridge which is probably a better fit for the Holbo. It was supplied with a head-shell 4-mm thick, but the bolts slots are recessed by over 2-mm.
A quick internet search turned up bolts made of stainless steel, titanium, aluminium, brass, plastic and nylon. Some brass bolts are gold-plated (for corrosion resistance presumably). As a one-time metallurgist, I know that stainless steels can be non-magnetic, or magnetic.
Plastic and nylon are lightweight insulators and immune to electro-magnetic effects like induced eddy currents.
The lower the material density, the lower effective mass of the cartridge. Here brass is clearly the worst, being denser than steel and weaker than the other metals.
I presume that the main engineering requirement is to firmly couple the cartridge to the tone-arm but I have no idea how firmly.
The Funk Firm has an opposite view with its Houdini coupler which in effect splits the bolts in half, with an elastic suspension between the cartridge body and the tone-arm. It seems to allow the cartridge body to swing easily to the left or right side. Does anybody here use these?
LMAO I have a digital scale that I thought was accurate. It was off by a full gram!!! so instead of 2gr my vtf was set to 0.9 and distortion like I’ve never heard before. |
Cartridge bolts contribute significantly to a cartridges total weight once a cartridge is mounted. Aluminum is light, immune to hysteresis and readily available. Choose only the length you need. You only need enough torque to permanently hold the cartridge in place once you’ve aligned it properly. You want to avoid deforming the cartridge body and the head shell from too much torque! For VTF I’ve always used the Shure SFG II which is precise, repeatable and as accurate as it needs to be. Always at the ready since you don’t have to worry about the battery discharging when it’s been sitting unused for years at a time. The only issue is availability since it was discontinued by Shure when they abandoned their cartridge business. |
@faustuss I really like the Riverstone Audio gauge. You should check it out. |
In my several decades of experience with it, the SFG was imprecise and results were often not repeatable. Plus it could damage a cantilever if one were not careful. These days it makes no sense not to use a digital scale, just making sure that the one you choose has its weigh pan in the plane of the LP surface. if eddy currents through cartridge hardware is sensed, you have super human sensoria. Sheesh! I think this whole issue of cartridge hardware is a bit silly but FWIW titanium is a very poor conductor. |
I've just ordered some aluminium bolts because they just might be long enough - will be arriving in the new year on a slow boat from China. postage was nearly twice the $7 cost of the bolts. Will likely get some stainless-steel ones when I can find them. The only affordable titanium bolts I have found that will ship to Australia come in a 50-pack! |
