What's the Difference between a Head and a preamp?

Surprise! Panda! You're not a noob.

A head is a preamp plus a power amp in one box. If you just have a preamp, you need a separate power amp to drive the speakers.

Basically, a preamp boosts the signal from your bass so that it is "hot" enough to drive a power amp. Plus it gives you tone shaping options such as EQ (and on fancier preamps, perhaps compression, effects, etc.)

 

Most amps have what's call a preamp section. And on most rigs you can bypass this preamp through the effects return so that you can color the signal with some other device (e.g. SansAmp BDDI box). The preamp section is for coloring the sound before going to the power amp section.

The other side of the equation is the power amp of the head. It's job is to amplify the preamp or re-directed preamp signal. It just amplifies. Most bass heads have both the preamp and power amp, although you could buy just a power amp.

 

A preamp takes the small signal from your bass, and turns it into a marginally larger signal. They come equipped with all manner of tone shaping circuitry, but probably don't put out more than 3v or so.

A head has (usually) a preamp built in with tone shaping circuitry, but the preamp in the head feeds into a POWER amp section. That way you don't need a separate power amp to hear all that wonderful tone shaping.