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Turntable preamps are components in a stereo system linked between a turntable and receiver. For systems designed with sound quality in mind, these components often come separately, though they are sometimes integrated within the receiver itself. Vibrating signals caused by a stylus, or needle, on a record must be amplified many times in order to be reproduced into normal hearing range or public address levels. The preamp, short for pre-amplifier, processes the signal from the tonearm cartridge, stepping up its power, or splitting stereo signals into different channels for separate speakers. Common types include solid-state single stage, or op-amp; moving magnet, moving coil and wideband; and traditional vacuum tube.
In function, turntable preamps differ from ordinary preamps due to their frequency responses. Vibrations translated through record grooves and tonearm needles create multiple frequencies picked up at different levels by the varying magnetic cartridges of tonearms. Turntable preamps equalize signals in order to maximize signal-to-noise ratio for cleaner sound and more precise amplification. These devices are also known as phono preamps, phono stages, and Recording Industry Association of America (RIAA) preamps.
Types serve the particular technology of a tonearm cartridge. Essentially, these can differ in whether a small vibrating magnet induces current between fixed sets of coils, or a small coil induces current within a permanent magnet. Technical differences affect accuracy and noise of a turntable's signal reproduction, as well as costs and user preferences for sound.
Moving magnet turntable preamps require at least 10 times less gain, or signal power amplification, than moving coil types. This is because moving magnet cartridges can follow grooves more closely with less pressure. Consequently, less amplification is needed for an equivalent performance to moving coil components, which generate higher gains and more unwanted noise.
Conversely, moving coil types generate a lower output of around 0.5 millivolts (mV) to the moving magnet's 5 mV, and so are often used with a step-up transformer. The moving coil cartridge possesses fewer coil windings, is more susceptible to noise, and is generally more expensive than the moving magnet type. In addition to these two types, digital chips called op-amps modernize the technology, varying sound reproduction quality from poor to very good.
Inclusion of turntable preamps in a stereo system or disc jockey setup permits a more uniform processing of varied components. These can include compact disc, tape, and television audio. This function typically serves components that don't require complex mixing. Some equipment can also process signals from dynamic microphones and musical instruments, making these units a flexible backup for complex or live entertainment audio systems.
Equipped with conventional cabling jacks, some turntable preamps are also outfitted with Universal Serial Bus (USB) jacks. This technology permits the transfer of records to computer formats. Components might possess their own sound cards and be specially equipped for handling large audio files.
Wideband types of turntable preamps increase signal processing in the high-frequency range. This is in addition to maintaining the middle and low frequencies, while reducing audible defects. Noise creeps in from the stepping up of signals and operation of equipment. Technologies feature varied characteristics that make it necessary to listen carefully — not only to evaluate the quality of reproduced sound, but to evaluate the equipment itself without any music signal. The resulting sound qualities of these components very often come down to a matter of subjective preference and debate.