Preamp - what's the purpose?


Intentionally dumb question...

I've heard various 5-15W tube amps in my room. EL84, 300B, etc. They all have input stages and the output stage. I send them a line-level signal from a DAC.

Sitting a few meters away from my loudspeakers, the first watt alone gives me roughly 80db of volume. I think these amps are biased to expect the line level signal directly. Why wouldn't the designer do that?

So what's the point of adding a pre-amp? Why do people do it?

thanks in advance

 

clustrocasual

Thanks for the replies. The obvious answer is regarding sources and level control. I wondered about people who use it to color the sound, as some salespeople have said "it just sounds _better_ with the ($5-15k) preamp!" and based on the gear they were talking about, it seemed kinda BS. But I know there are power amps which the designer biased on the low or high side.

I think if I needed input selection or attenuation, I would try to build or look into buying a passive pre-amp... 

@clustrocasual -- "I wondered about people who use it [a preamp] to color the sound..."

Its been explained that "colored sound" can also happen when there is a mismatch between the source's output and the power amp's input. 

You can't just assume that all line level sources are capable of optimally driving a power amp. Sometimes that's true, and sometimes its not.

Never been a fan of preamps. The main course is the amp, preamp is like adding salt n pepper.