Preamp - what's the purpose?

either is ok, modified sound with pre or pure sound with no pre.

once you feel pure taste with no sauce, you will remove the preamp!

@r27y8u92 I have LPs and CDs I recorded. I find that using a preamp gets me more neutral sound as the preamp is able to eliminate the coloration caused by the interconnect cables- if you've ever auditioned interconnect cables and heard a difference, you know what I mean.

I've also found that quite often if a passive control is used, when turned down from anywhere other than all the way up there is a loss of impact across the audio band- usually most noticeable in the bass. This is caused by the passive control being in series with the output impedance of the source (which might be a DAC). Active preamps do not have this problem.

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?

In a smaller system you might not need a preamp. If you have multiple sources (tuner, tape, phono, TV, etc) you might. Most sources cannot drive long cables very well; if you want the best you have to use monoblock amps so they can sit by the speakers, allowing you to keep the speaker cables as short as possible.

A good preamp can drive long interconnects without the interconnects imposing a 'sound'- so it can be more neutral. You don't need to sacrifice any transparency or 'air' with a good preamp.