If you're experiencing a low signal level when you plug a turntable into your stereo or computer, there's a simple fix for that. A record player preamp is what you need. Most stereo components like cassette and CD players are at "line" level, but turntables only have an output of a few millivolts. A phono preamp boosts the output signal up to line level.
Older stereo receivers usually had a phono preamp built in, but the advent of CD's gradually eliminated the phono channel altogether. Attempting to play an LP on a modern stereo system with no preamp will result in very low volume, or no volume at all.
Connect the colour-coded jacks of the stereo cable from the turntable's left and right audio output plugs to the stereo input jacks on the back of the preamp.
Take a second stereo cable and run it from the stereo output jacks on the back of the preamp to the "Phono" channel on your stereo receiver. If your receiver does not have a phono input, you can use the "Auxiliary" or any other available channel.
Power on your amp, turntable and speakers. Select the correct channel on the front of the receiver -- either "Phono" or "Aux."
Play a record on the turntable. You should now have plenty of gain. Listen for any hiss or hum. If all sounds good, the connection was made properly.
See "Warnings" section if you hear a 60-cycle hum. This will need to be addressed.
If you prefer to connect the turntable to your computer, a phono preamp is still necessary. There are USB phono preamps available that are designed specifically for computer use with a sound card built into the unit. Most USB turntables available on the market do not score very high marks with audiophiles. It is recommended you do some extensive research before investing in a USB turntable if you want professional-sounding results.
Make sure to properly ground your turntable; an ungrounded turntable can produce a very loud 60-cycle hum. To do this, connect a ground wire between the ground plug on the back of the turntable and wrap around the "Ground" knob on the back of the preamp. If this does not cure the low-frequency hum, try some of the other fixes described in Reference 1.