High end stereo preamps? Worth it?

Many posts saying hi-end preaamps improve sound.
One post saying 'why', surely the additional circuitry cannot improve the signal it is fed with.  Doesn't it just add noise?
Or does it add some aspect to the sound that these posters find pleasing?
Can somebody who understands the tech please tell me.

YES.  When I first plugged in the Audio Research SP-3 pre-amp in 1974, in my shop, I had a true revelation in how systems can sound.

Obviously, in the many years since then pre-amps have evolved and even improved somewhat.  I suggest you work with your local dealer and audition as many as he carries IN YOUR ROOM to find the one YOU like best.

It will be as much a revelation to you as it was to most of the rest of us who have been down this road before.

This is not to say that there are not some SS pre-amps that are very good, because of course there are. However, the one that sounds best IN YOUR ROOM is the one you need to purchase and be delighted with in your system.

Cheers!

Surely its not just more components adding more ’noise’ - its a question of WHICH sort of components and WHICH sort of circuit implementation, no?
Maybe a drastic example of my own, a run of the mill mid/low-fi Rotel preamp I’d replaced by a Levison no. 326S preamp.
The difference like day and night. Maybe hard to believe - but that’s what can happen, and I’m pretty sure will happen - so long you own speakers, amp etc. that will match the ’new’ setup.
Cheap shoebox speakers and or low-fi amp will possibly just paste over the difference.
So as always it’s ’horses for courses’.
And the best expensive cable will NOT make any difference with a low/mid-fi preamp. Tried that of course too. Nada.
M. 🇿🇦

clearthinker129 posts

Many posts saying hi-end preaamps improve sound.
One post saying 'why', surely the additional circuitry cannot improve the signal it is fed with. Doesn't it just add noise?
Or does it add some aspect to the sound that these posters find pleasing?
Can somebody who understands the tech please tell me.

Many have posted how a quality preamp improved their systems.  None will be able to tell you the science.  To many of us, It just sounds better..  Bascom King, in his interview on inserting a preamp, states "the music is more compelling and real"  Compelling and Real.  I don't think we will ever measure these qualities, but I know I can hear it, or at least I am convinced I am, and convinced enough to own a nice pre amp. 

First- one premise made by the OP is incorrect- phono stages are not noise free. Some are very quiet but none are dead silent. 
Next, I’ve been messing around in this audio world since the 1970’s. Everything makes a difference and a great preamp can make a system and a dud of a preamp can break a system. More so, I believe, than can different amps.