How Does A Turntable Work?
There are several factors affecting the quality of sound
a turntable can deliver, and it can be very, very good. These factors are the base, the motor, the
bearings, the tone arm, the cartridge, and the diamond needle.
Bit of background here. The turntable
was invented by Thorens over 100 years ago to improve the sound of the cylinder
technology at the time. But while the turntable is still going round,
cassettes, 8-track, open reel tapes have disappeared, MP3’s and CD’s fading
away.
But what magic is this? A needle scraping across the groove
of a record, delivering beautiful and accurate sounds? We’ll get to that in
another blog.
Let’s start with the base and motor of the
turntable. First it must be heavy, to provide a steady platform for the record.
Obviously it must be perfectly level so that the needle presses equally on both
sides of the groove. A good brand will have adjustments for that. To make a
record spin at 33rpm is easy enough, but any variations, called “wow &
flatter” can be heard. “Wow is a relatively slow form of flutter (pitch
variation) which can affect both gramophone records and tape recorders. In the
latter, the collective expression wow and flutter is commonly used.” Imagine a single note of a piano
varying in pitch as it fades away? Even tiny variations may not be obvious, but
listeners will say they don’t like it. So the motor has to have rock solid
accuracy, and no noise from the bearings, a fault known as “rumble,” and heard
on all cheap turntables. To help the speed accuracy the platter material should
be heavy. This inertia effect is like a car’s flywheel.
Looks solid? That's because it has to be. With turntables quality of materials and manufacture matter.
Driving the platter round and round can be done
three ways. Originally a rubberised wheel pressed against the inside of the
platter. This noisy arrangement was called “rim drive.” To stop all the
mechanical noise a large rubber band was used for rotation, and is known as
belt drive. It allows the heavy platter’ mass to be isolated from the motors
tiny variations, as well as being noise free. This is now the most popular and
common utilised by quality turntable manufacturers. Direct drive relies on
electronics and the heavy platter, which becomes part of the “motor.” These
dominated sales for years, and now are favoured by disc jockeys who abuse every
known rule to make their distinctive scratching sounds.
My next blog will be on turntable tone arms.
Digby Paape is Wellington’s best known audio
expert, and has been writing, commentating, and selling HiFi since 1972. He is the owner of Associated Audio Ltd.





