Many vinyl records are manufactured with an oversize spindle hole, and some turntables have undersized spindles. These conditions can result in pitch variation from not being able to center the record onto the spindle, which causes eccentric rather than concentric rotation of the record. To solve the problem, I created a custom record centering accessory, intended as a quick and simple way of centering vinyl records with oversize center holes.
This compact and lightweight accessory is simply placed on the center spindle of your turntable over the record and twisted into position, which locates the sharp edge of the device between the spindle and the record hole, taking up any excessive clearance.
The bore and conical outer surface of the centering accessory are concentric within 0.00002 of an inch (0.5 µm), ensuring that the center hole of the record is perfectly concentric with the spindle.
If a record is rotating eccentrically, the difference in linear velocity will cause a periodic change in speed, audible as a once-per-revolution wow.
A tight fit between the center spindle of the turntable and record hole is the usual means of ensuring a record is centered for playback.
However, due to manufacturing tolerances, some records have oversize holes and some turntables have undersize spindles, preventing the record from establishing a positive location, unless a tool like the one shown is used.
The record centering device in use.
The advantage of this method of centering is simplicity and speed. The limitation is that it will only center the record based on the center hole location. The groove structure on a record, however, is not always perfectly concentric with the center hole.
The master disks used in the vinyl record manufacturing process are cut on a lathe and subsequently electroplated to create the stampers that will be used to press the multiple copies of the vinyl records. During this process the original center of the lathe is lost. The stampers are manually centered prior to pressing, by an operator observing the locked groove at the end of the record under a microscope. Each record manufacturer has their own definition of what constitutes an acceptable centering tolerance for their product, and in addition, there is always the possibility of human error that would only be detected if there are strict quality control procedures in place, both at the pressing plant and at the receiving end (the record label ordering the records).
If, due to the aforementioned manufacturing and QC considerations, the groove structure of a record is not concentric with the center hole, then an accurate location of the center hole would still result in eccentricity and speed errors. The accessory presented here cannot solve this issue and there is no quick and simple way to compensate for such errors on domestic reproducing equipment. This accessory will only fix eccentricity caused by oversize record holes, again, provided that the groove structure is concentric with the center hole.
The centering device when not in use.
The centering accessory can be left in place during playback, or carefully removed, as preferred.
This project was commissioned by George Vardis, an EMT turntable enthusiast in Athens, Greece, who came up with the concept after becoming frustrated with the lack of repeatability when measuring wow and flutter with his Audio Precision system and Hewlett-Packard spectrum analyzer, due to the test record having an oversize hole. He turned to our company, Agnew Analog Reference Instruments, for the engineering and manufacturing of this accessory.
Please contact Agnew Analog Reference Instruments at info@agnewanalog.com for pricing and availability.
In the photos, the centering accessory can be seen on a Thorens turntable with an SME tonearm and van den Hul moving coil cartridge.
Note: This article was first published as a blog post on the Agnew Reference Analog Instruments website. It appears here in edited form by permission of the author.
