Belts.

Someone in the group was asking about these seemingly cheap components earlier, and the advice for replacement from many quarters was to buy a genuine replacement. The Thakker was also mentioned, and I have found it’s a good second best, but alters platter speed. This isn’t a problem if you’re confident in adjusting the motor tilt. The Linn belt is £50 and many people look to alternatives that are cheaper. The Linn belt cost was under £20 for a long time, and this is reportedly because in the early days they bought many thousands of them and stored them for years to be used as required. When stocks were discovered to be dwindling, they’d have had to find a source of replacements, and found that manufacturing costs were high. Why should this be?

By utter coincidence today I found myself working for a very wealthy chap who had made his fortune in Rubber Goods (lucky chap) and had during his career made turntable mats and belts for several hifi manufacturers. I mentioned the Linn belt price, and he said that the unit cost was probably only a couple of quid a pop, but... and it’s a huge one... the setup cost for the mould and finishing gear could be £15,000 upwards. Considering that Linn don’t make thousands of LP12s, it would therefore be a long time before costs could be recovered. £50 retail is not out of the way at all. Rubber goods manufacturers usually get the client to front the cost of moulds and machinery, then charge for the unit cost per item. For turntable belts it’s much cheaper to get a series of moulds made at the same time, so if you’re making many sizes of belt as Thakker would be, the setup cost per belt type is a fraction of the cost of that for making one belt type. The more popular sizes would thus be subsidising the more exclusive ones.

The cheapest way to make a turntable belt is to cut and join a linear strip of rubber, but this results in a join which may have a different characteristic of stretch even if ground to be dimensionally correct. This will result in impaired performance. Linn belts are not made in this way.

The belt thickness and width both influence platter speed, especially on a barrelled pulley as used in the LP12. The thicker the belt, the faster the platter. This is because the pulley diameter is measured across the physical pulley and platter, plus the distance to the neutral axis of the belt. (The neutral axis is the part within the rubber that is neither in tension around the outside of the belt, nor in compression nearest the pulley. It’s somewhere close to the middle of the belt thickness, but not quite!) Thus material is also important because this influences where the neutral axis lies.

The width of the belt must be uniform and correct to spec, otherwise it will ride up and down the pulley causing wow and flutter.