[krmathis]

Preamplifiers are mainly used for:
* Volume level controlling
* Sources selection

 

[kramer5150]

Selecting between multiple sources. Some implement tone shaping as well. Some are merely used for tone shaping prior to amplification, and don't have multi-source inputs.

 

[manhattanproj]

going on this similar topic, what's a loop out?

 

[Lord Chaos]

Loop out is used for external processing: a dbx expander, a noise-reduction unit, an equalizer, etc. The signal goes out to the offboard device, is processed, then comes back to be listened to.

Signal levels of stereo gear range from -70dB for moving-coil phono cartridges, around -60dB for moving magnet or moving iron, -50dB for a microphone, -10dB for most "line-level" sources such as tape decks, tuners and CD players. A pre-amp is a separate component that includes all the various inputs and allows control of them, which is why they're often called "control amps."

The simplest way to handle all of this is to buy a "receiver," which is the common term for a component that includes all of the above. It has a phono pre-amp (also known as phono stage) that applies the necessary equalization to the signal from the cartridge. It has a tuner built in. Some have a mic input (I used to use a Marantz 1060 as a mic preamp for recording; note that the phono stage applies the right amount of gain but has different EQ) you can use for various purposes. It has the loudness compensation circuitry and all the other controls, and the power amp. All in one box. They work well.

Separating the pre-amp from the power amp offers some advantages. Pre-amps have to apply a lot of gain to some of the signals so you don't want those circuits near the hefty power supply the power amp uses.

Pre-amps can be simple or complex. I now use a Benchmark DAC as my pre-amp as all of my sources are digital. Deluxe pre-amps can apply EQ, room reverb, balance and various other things.