If you're new to vinyl and unsure what's required to get a turntable up and running, at least the electronics required, this guide should answer most, if not all, of your questions.
A complete turntable is comprised of three different parts: a device for physically turning records, a tonearm to hold the cartridge (often refered to simply as "the arm"), and a cartridge to produce the signal. The cartridge houses the stylus, which is the tiny part that actually comes into contact with the record and traces the groove. The stylus may or may not be replaceable.
The part which simply turns the record, which is sometimes refered to, confusingly, as "a turntable" is also known less ambiguously as a motor unit. At the higher end of the price spectrum it is common for the motor unit, arm and cartridge to be purchased as separate items, often from different manufacturers. With more modestly priced equipment it is more usual for the motor unit and arm to be purchased together as a combined unit, sometimes with a cartridge already fitted.
Most modern music playback devices such as CD players and MP3 players output a signal of the order of a volt (roughly), and frequencies across the audio spectrum are outputted with equal intensity. These devices contain lots of electronics to achieve this. However, turntables are very different. A turntable is essentially a mechanocal device and its output is a tiny signal of the order of a few millivolts or less. The signal is generated by the motion of the stylus as it traces the groove. The way it works is to have tiny coils of wire within the cartridge moving relative to a magnetic field as the stylus moves from side to side whilst tracing the record's groove. It is, in effect, a tiny electric generator. However, being so tiny, it produces a tiny voltage. This voltage needs to be amplified to raise its level to something comparable with CD players etc, so that a typical domestic system amplifier can handle it. But there's an added complication - vinyl records are recorded with bass frequencies severely reduced and treble frequencies seriously boosted. The reason for this is to prevent bass frequencies from taking up too much space on the record (which would reduce available playing time) and to prevent treble frequencies from taking up so little space that surface noise would drown them out. This bass cutting and treble boosting is known as pre-equalisation or pre-emphasis, and on playback the opposite must be done to restore the correct balance, ie the bass must be boosted and treble cut.
what is RIAA?
RIAA stands for the Recording Industry Association of America, who set a standard in 1954 for the precise amount of bass cut and treble boost to be applied when records are made, and the converse boost/cut required when records are played back. There were numerous different standards of cut/boost before 1954, each requiring amplifiers with different playback characteristics to achieve accurate reproduction, but the RIAA specification became universally adopted and allowed all record manufacturers and amplifier manufacturers to work with a common standard. All modern records are cut to the RIAA standard.
So, a turntable requires a special amplifier to raise its output voltage to about a volt, and apply RIAA equalisation so the record sounds as it should. This device is known as a phono pre-amp or a phonostage amplifier.
different types of cartridges
There have been several different types of cartridges produced over the years, but the two which are common today are known as moving magnet cartridges and moving coil cartridges. Moving magnet cartridges, often abreviated to mm, are the most common and are the type found at the cheaper end of the price spectrum, though there are plenty of high quality and expensive moving magnet cartridges available too. They work by having fixed coils of wire (one for each channel in a stereo cartridge) and a magnet which is moved relative to them by the motion of the stylus as it traces the record's groove. Moving coil cartridges on the other hand work by having fixed magnets and coils which move as the stylus traces the groove. They are generally more expensive than moving magnet cartridges. The advantage of the moving coil principle is that coils of wire are lighter than magnets and therefore can be moved more easily. The disadvantage is that moving coil cartridges put out a lower signal than moving magnets, by a factor of about ten. The large difference in signal levels between the two types of cartridge means that the phono pre-amp must amplify an mc cartridge more than it does an mm cartridge.
Incidentally, many moving magnet cartridges have a stylus which can be replaced without the need to purchase a whole new cartridge. Moving coil cartridges usually have a stylus which can't be replaced, requiring the replacement of the entire cartridge when the stylus becomes worn.
Some phonostages are compatible with both mm cartridges and mc cartridges, usually having a switch to select which type of cartridge it is set for, and some are compatible with only mm (or mc).
A low output moving coil cartridge can have its output raised to that of a moving magnet cartridge by using a step-up transformer, allowing it to be used with a phonostage set for moving magnet amplification. This route can yield extremely high quality reproduction but is expensive and relatively uncommon - usually adopted only by the most serious audiophiles.
the complete playback chain
So, in order to play back records, a turntable with arm and cartridge is required, plus a phonostage which is then fed into an amplifier which drives a pair of loudspeakers. Before CD players were invented, and up until the mid 1990s, it was normal for amplifiers to have a phonostage built-in to them, with one input on the amplifier labeled "phono". The built-in phonostage was often, though not always, compatible with moving magnet cartidges only. Many of these older amplifiers are still in use and if you have one you don't need an external phonostage unless the built-in phonostage is mm only and you want to use an mc cartridge. If you do want to use an external phonostage with an amplifier which already has a phonostage built in you can simply feed the external phonostage into one of the spare line level inputs, often labeled auxiliary or aux, though the CD input, tuner input etc. can be used too. "Line level" simply means an input designed for signal levels of about 100mV - 1V and not requiring RIAA or other non-linear amplification. Pretty much all the inputs on modern amplifiers are line level inputs.
In more recent times a lot of loudspeakers which don't appear to require an amplifier have become available. In actual fact, they don't require an external amplifier because the amplifier is built into one of the speakers. These are common for use with, for example, computers. Built-in phonostages are not usually included with these amps/speakers and an external phonostage will be required for playing back vinyl.
combined turntable/phonostage packages
Another recent development is the introduction of turntables with a phono pre-amp built in to the turntable plinth. These devices put out a line level signal and do not require an external phonostage, or a phonostage built in to the following amplifier. Sometimes the output is in the form of a USB connection to make it possible to connect the turntable directly to a computer. Although some of these products are of hi-fi quality, quite often they are simply a convenient way to minimise the number of boxes and expense involved with a separate turntable and phonostage. Often they are of only modest quality and not really suitable for serious audiophile use.
So, in general, the requirements for playing back vinyl are a motor unit, arm, cartridge and phonostage, making sure that the cartridge and phonostage are compatible. The motor unit and arm probably will be bought as a combined package and called a turntable, and the phonostage may be an external unit or may be built in to the amplifier which is used to drive the loudspeakers. Possibly, though not commonly, the phonostage will be built into the turntable.
This should be enough information to get you started with vinyl, but of course there are many other things to consider if you are looking for the best possible performance. Beyond the scope of this article are considerations of compatibility between the tonearm and the cartridge, how to align the cartridge properly etc. A search of the internet should find lots of information on correctly setting up a turntable’s mechanical parts.