The signal that comes from your "sources" (CD player, turntable, tuner, etc.) feeds the preamplifier, which in turn sends a conditioned and somewhat boosted signal to the power amplifier. Many home audio setups contain an integrated amplifier that combines preamp and amp into a single housing.

Many amps need nothing more than a good cleaning and a bias adjustment to sound good. In others, a better power cord, better diodes, filter capacitors, and interstage coupling capacitors can improve the sound. Older amps in particular will likely need new electrolytic caps, which dry out over time. Power and integrated amps that tend to run hot may last longer if provided with a whisper fan cooling circuit. High quality opamps can also improve preamp circuits. Check pricing here.

photo courtesy Rega Research Ltd