MANUAL OF ANALOGUE SOUND RESTORATION ... - British Library

y, the groove. “Tracking” concerns the alignment of the reproducer compared with the
geometry of the original cutting lathe.
4.2 Basic turntable principles
I assume my readers know what a turntable is, but they may not be aware that the
equivalent for cylinder records is called a “mandrel.” My first words must be to encourage
you to use “a good turntable (or mandrel) and pickup”. It isn’t easy to define this; but to
recover the best power-bandwidth product, the unit must have a lower background-noise
and a wider frequency-range than any of the media being played on it. This is something
we can measure, and does not need any “black magic.”
The unit should also have reasonably stable speed, although we shall come to a
technique in section 4.16 where this need not necessarily be to the highest standards. In
Chapter 4 we shall be studying the problem of establishing the correct playing-speed for
rogue records. These are in the minority, but at least one machine must have variable
playing-speed so this matter may be researched. (It may be necessary to have two or
more machines with different features to get all the facilities).
The unit should be insulated so it is not significantly vibrated by sounds from the
loudspeakers, loose floorboards, etc; this may mean fixing it to a massive mounting-plate,
and suspending it in compliant supports. All this is good engineering practice, and needs
no further comment from me.
Rather more difficult to define is that the unit should have “low colouration.” This
is much more a black magic subject. Basically it means that the wanted sounds are
reproduced without “hangover” - that is, the machinery should not contribute resonances
or sounds of its own which continue after the wanted sounds have stopped.
The main point about hangover is that the stylus and record themselves generate
it. As the stylus is vibrated by the groove, reaction-forces develop in the disc or cylinder
itself. It is important that such vibrations are quelled instantly, especially in the presence of
clicks and pops. When we remove these clicks and pops using electronic techniques, we
may not be able to get a clean-sounding result if hangover exists in the record itself or the
pickup arm.
To deal with the record first. We cannot prevent the vibrations being set up; we
can only ensure they are eliminated as quickly as possible. One method is to use a heavy
rubber turntable-mat in close contact with the back of the disc. The only suitable kind of
mat is the kind with a recessed area about four inches across in the middle, so the disc
makes good contact irrespective of whether the label-area is raised or not. As I say, it
helps if the mat is thick and heavy; the kind with lightweight ribs is pretty ineffective.
Some vibrations can also be attenuated by a clamp - a heavy weight placed over the
record label.
The Pink Triangle Turntable is designed without a mat at all. It is made from a
plastics material of the same specific gravity as vinyl. Any vibrations set up in the vinyl are
efficiently conducted away without being reflected back towards the pickup. Basically this
is a good idea, but it cannot give perfect reproduction unless the disc is in intimate contact
all over. You should be prepared to flatten warped records to cut down wow and tracing
errors, anyway; please see Appendix 1 for details. In my experience, Pink Triangle’s
method is as good as the best turntable mats, but not better.
I can see no virtue in “anti-static” turntable mats, especially ones that aren’t thick
and heavy. A more suitable method of neutralising electrostatic charges is to keep an
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