If you have a decent valve amp, how do preamp's enhance your sound?
preamps shape your tone and boost the signal from instrument level to a level appropriate for a poweramp. Poweramps amplify the signal to drive speakers. Each adds it's own character and coloring to your tone, and you need both to have a functional amplifier. People use different preamps to have different voicing options, so it can sound like a completely different amp. You can use different combinations of preamps and poweramp, but you need both.

combo amps have a preamp, poweramp, and speakers in one unit.
heads have the preamp and poweramp in one unit.
rack units are seperate so you can mix and match.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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They just add preamp distortion. it doesnt neccesarily enhance your sound, but if you have just a power amp, then it would make a difference. your valve amp already has a preamp.
i saw a guy on youtube using a mesa boogie preamp with a 5150 head which sounded amazing (type in mesa boogie and he is first on youtube).
Quote by avalanche930
Ive heard better out of just a 5150 without the mesa preamp.

new that one was coming. bear in mind its on youtube, you tube.