Finding a replacement drive belt for Thorens suspended sub-chassis model turntables
Drive Belts and suspension: Thorens suspended turntables isolate the platter and tonearm from electric motor vibrations by utilizing a separate chassis suspended by springs, and by an elastic drive belt. In the case of the TD125/6, 14x, 15x, 16x models, three conical coil springs are located under the floating sub-chassis. The TD125/6 differs from the others because it supports the springs from below by adjuster cups located in a metal tray. The TD 14x, 15x and 16x models hold their springs on three steel studs that hang downward from the top plate. In each case, the springs are located below the platter bearing.
In all of these designs, the belt itself is an important part of the overall suspension scheme. The job it must do is not simple. The flat belt drives the inner driven-platter by grip. In order to produce exceptional sound, the belt must maintain constant velocity between the motor pulley and the driven inner platter. Any belt slippage or variation in rotational speed of the driven-platter caused by belt action will degrade sonic output. At the same time, the belt is relied upon to allow independent motion of the suspended chassis. In reality, the belt will exert some influence on the action of the floating sub-chassis. Be sure that all this was taken into account by the original designers. The belt is an integral part of the suspension design.
Belt tension and the motor: Belt tension (and belt elasticity) not only affects suspension operation, it also affects motor noise. If there is too much belt tension, the motor shaft will be forced into hard contact with the upper motor bushing.....causing excessive motor vibrations to be introduced into the chassis. The result is dull, lackluster sound quality. Too little belt tension and there will be slippage at the drive pulley (lack of dynamic snap). Either condition is to be avoided.
Above: The outer platter of a Thorens TD150 is removed to show the driven sub-platter, belt, and the driving motor pulley. In this photo an original equipment replacement belt has been sourced from the North American Thorens distributor. (Acoustic Sounds)
above photo: some NOS Thorens drive belts purchased from a Thorens dealer in Athens (2004). pn# Z6800574 (thanks to Thomas Kamvoussioras for sending in this photo)
Correct dimensions for the popular Z6800574 belt:
Q: How often should I replace the drive belt?
A: Approximately every three years. It varies depending upon atmospheric conditions and also the amount of use the turntable gets. In certain climates with high air pollution the rubber belt can deteriorate more quickly than in other areas where air quality is more benign. Additionally, a worn belt will be evident by its stretched condition
Above photo compares a new replacement belt with a worn belt. The longer belt is the worn one.
Q: How can I tell if a belt is worn out?
A: Worn belts will be stretched. In an extreme case, the stretched belt will slip at the drive pulley and possibly tend to fall off due to inadequate tension. Poor shifting between the 33-1/3rd - 45 rpm pulley steps has also been noted as an obvious sign of belt stretch.
basic rule: replace the belt every three years.
Thorens drive belt part numbers:
Rutherford Audio is the North American Thorens Distributor and also sells official Thorens replacement belts from their website at this link:
Q Audio: http://www.qaudio.com, has genuine Thorens replacement belts with the Thorens Logo. I have not yet purchased from this vendor but this vendor has been an authorized Thorens dealer for several decades.
Turntable Basics, http://www.turntablebasics.com/ cross references belt substitutes at $10 each. I have not tested one of these belts. Reports by other users suggest a wider belt with a thicker cross section. Some have reported finding a workable size by trying progressively longer belt lengths until good function is achieved. These are not original equipment replacements. However the seller is reputable and will work with the buyer to find an appropriate belt length that seems to work. Personally, I prefer using the correct belt in the first place.
If you know of any vendors offering correctly dimensioned Drive belt replacements for Thorens please contact me so that I may list them here: