The Pre-Amplifier is sometimes known as the Control Amplifier in a HiFi system.  It is the device that provides greater control of the sound from volume control, equalisation and input/output selection.  Pre-Amplifiers should ideally be sonically transparent.  However interesting and often very pleasing results can be obtained by pairing a valve pre-amplifier with a solid state power amplifier, or vice versa.  One of the greatest benefits of using separate pre-amp and power amp components is the ability to mix and match to find the perfect combination for your ears.