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A record player preamp is a necessary piece of gear for increasing the signal of a turntable. While CD players, cassette decks, and other stereo components have plenty of gain, turntables produce much lower output and require additional amplification. That's where the record player preamp comes in, giving turntables the extra boost they need. Phono preamps were commonly built in to older stereo receivers and power amps so that the turntable could be directly connected. Due to the consumer migration from LPs to CDs in the 1980s and 90s, most newer stereo systems don't even have a phono input at all, much less a preamp built in.
Therefore, a record player preamp must be used on newer stereo component systems. For those who might be looking to transfer a collection of old vinyl LPs to a digital format, selection of a quality phono preamp will be essential. While a high price doesn't always guarantee high performance, it generally holds true that cheap record player preamps do not produce adequate results. To reduce background hiss, it's important to choose a record player preamp with a high signal-to-noise ratio; the higher the ratio, the lower the hiss.
Part of a phono preamp's job is to provide the proper RIAA equalization. Vinyl records have a special equalization curve known as the "RIAA curve," a specific equalization curve developed by the Recording Industry Association of America. This EQ curve is applied when the signal passes from the turntable through the phono preamp, restoring the recorded music to its original fidelity without coloring the sound.
Some modern vinyl record enthusiasts prefer to connect the turntable directly into a computer for burning CDs of their favorite LPs. A preamp is still needed to bring the record player's output signal and impedance up to the line level of a computer's sound card input. A popular alternative to the analog preamp is a USB phono preamp designed especially for use with computers. An external USB preamp has a sound card built in to the preamp for the purpose of working with large digital audio files, such as burning an entire album side at a time. Since most PCs internal sound cards are part of the motherboard, they often deliver inferior sound quality and are not always up to the task of high-fidelity audio restoration.
Most turntable preamps also have line inputs for connecting cassette decks, CD players, radio tuners, or televisions when needed. More advanced models feature optical in/out ports, which can be used to connect devices such as MP3 players, DAT machines, or digital mixing boards. Nearly all record player preamps have a ground connection that helps reduce that problematic 60-cycle hum or "buzz" that often mars the sound from an ungrounded turntable. The record player's ground wire connects directly to the ground connection on the preamp.