Silicone motor mounts for vintage turntables

Motorupphängningar i silikon till USA-byggda studioskivspelare från 50- och 60-talen. Beklagar den engelska texten, men de här delarna har en begränsad svensk publik.

Upgrade motor mounts for about one half of the US vintage broadcast turntable brands, including at least Gates, QRK, RCA, Russco. (E. g. Rek-O-Cut and Empire decks have different motor mounts, which we do not make).

The parts have been developed and tested in cooperation with members at the Audio Karma and Lenco Heaven forums.

The original parts were industry standard isolators, put to a clever use for the mono playback of those days by allowing for a much freer movement vertically than horizontally. At the time this made a major part of the motor vibrations inaudible, since the early mono cartridges were designed to only register lateral (horizontal) movement. This advantage was lost with the advent of stereo recordings, cut in a V-shape with both a vertical and horizontal movement. While this wasn't much of a problem for the intended use of these machines in heavily frequency limited playback over AM radio, it was much more so for any hifi aspirations.

These new motor mounts are not copies of the orginals. Instead, they are cast with the inner isolator part and the outer frame in silicones in two different hardnesses. The opaque inner isolator part is much thicker than the original membranes, in order to even out the vibrations vertically and horizontally, while at the same time providing a more effective overall damping. The black outer frame is not in steel as on the originals, but a stiffer silicone than the inner part. This provides further damping of the motor vibrations before them reaching the top plate.

A set consists of one thinner and two slightly (ca 0,7 mm) thicker isolators for a correct balance of the motor carrier plate, just as on the originals. The different parts are marked with small dots: at 11 o'clock for the thinner parts, and at 1 o'clock for the thicker one, as illustrated above.

A set of five pairs of steel spacers and washers per mount is also provided. But please note, no screws are included. Since we cannot know every type of screw used in all the different models using these mounts, we expect you to reuse the ones you already have, or to find replacements yourself.

Another quirk is that while most machines using these mounts only needed two threaded holes for the original steel frame of each isolator in the top plate, we recommend drilling and tapping the top plate for using all four fasteners (or three in the narrower positions). Since the frames of the new mounts are softer than the originals, this will improve the stability of them. Some of these turntables were factory built with four holes; if yours is, use them all, regardless of how the originals were mounted. While using only two screws should still be workable, the mounts may get slightly warped by the weight of the motor, possibly affecting its position.

The parts are made and sold in a square shape only, as in the images. One corner can easily be cut for a snug fit in positions originally requiring elliptic mounts. For best results, remove as little as possible of the frame when doing this.