Today or in past applications there are about 3 different applications of Pre-Amplifiers

1. In Conjunction with a Condenser Microphone.
2. With or in a Amplifier or Receiver for a Magnetic Phono Cartridge.
3 A Tape head deck with no electronics.

In each case the voltage isn't strong enough on it's own to power a main amplifier without mass distortion.

Ampex made some tape decks with no electronics so you would have to get a pre-amp to play the tapes.
If you buy a Receiver or Amplifier with a Phono input the electronics are built in and no extra pre-amp is needed.
Sometimes with a condenser microphone the pre-amp is included with the Mic.

The RIAA Curve. When cutting a master disc to make a vinyl record there is a comensating circut that reduces the base frequencies so the cutting lathe doesn't cut back in the grove that has just been cut. This probably needs some adjustment of the levels.
This compension is added back in the electronics in a phono pre-amp so it all sounds ok. This curve is still used today.

A main amplifier circut needs about 1 volt peak to peak to drive it to normal levels. All other inputs on a receiver or amplifier is is set to use the 1 volt input without extra amplification.

I have seen where some people want a pre-amp that colors the sound. No such pre-amp is made. The only place where adjustments are made is with the tone controls on a receiver or amplifier.

Ray E. Strode