Preamp - what's the purpose?

Some people have multiple sources and need a switch.  I have 2 inputs but have an amp with 2 inputs.  My new amp I ordered custom has 3 inputs, one for a spare.  

Some DACs don't have volume control, so they use the pre for that.

Some people think a preamp improves the quality of the sound.  I say it can only color it.  

And I do it just like you--DAC into my tube amp.  

Jerry

Fair question. Obviously, you need a preamp if your amp has no volume control and you want to use more than one source and want to conveniently select between them with a switch. With some sources, you might need amplification to get to line level. Phono, for vinyl and MC or MM cartridges and no phono preamp, some digital sources (I remember an Apple Airport I used as a streamer some years ago needing quite a bit of volume addition from my Rotel Receiver.) If you want to use headphones but don't want to have a dedicated headphone amp, a preamp can provide. These days, other devices have assumed some of the preamp functions, so you could make do without a separate preamp. Many streamers have DACs and preamp volume, bass, treble and balance functions of classic preamps in their phone apps, some even have phono preamps and headphone amps with headphone jacks, functions which duplicate or replace those typically on a preamp. Depending on your use case, the need for a preamp could range from not at all to essential.

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.

The BEST sound comes from a TUBE PRE and a SS amp....PERIOD !