There are basically two types of turntables: powered and unamplified.
Some turntables are standalone devices, not a complete entertainment system. These types often lack a preamp.
What is a preamp? First, a little history.
To fit long playing music on an LP record, vinyl is generally recorded with lowered lower frequencies and boosted higher frequencies. This is called the RIAA curve. To capture audio from your vinyl, you need to make sure this curve is corrected. A USB turntable, (one made specifically for digitizing vinyl, in other words) will take care of all of this for you. Some audio input devices, designed for computers that lack a sound input port, will correct this as well.
Another problem with preamps is boosting these frequencies to normal levels when playing a record. You can rebalance the frequencies by modifying the equalizer settings in your audio software.
A third problem with turntables is low-frequency hum. If you hear this when you’re trying to preview a record, you’re hearing ground, because the turntable your preamp amplifies sound from is not grounded. You can correct this by wrapping your turntable’s ground wire around the bottom pin of a three-prong plug such as the one on your power strip and connecting it to a grounded electrical outlet.
Neither of these things is a problem for you when you buy a USB turntable, one made specifically for digitizing vinyl, or when you use a turntable that has a built-in stereo receiver. How do you know if your turntable has a stereo receiver? If your unit has a built-in AM-FM radio or cassette deck, you can be sure that it also has a built-in receiver.
You can avoid these hassles by purchasing a turntable made specifically for converting vinyl to MP3 format. Sony’s PS-LX300USB USB stereo turntable system offers a built-in phono preamp, static balancing tone arm, and fully automatic operation. The Ion Audio TTUSB 10 USB turntable for vinyl recording offers switchable phono / line level RCA output (with built-in preamp) and adjustable anti-skid control for enhanced stereo balance.