How does a turntable work? - The base

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.