I can't tell a difference between 4 phono preamps

[mhardy6647]

Hearing blacker blacks is a synaesthetic thing, yes?
(or maybe a lysergic thing, I suppose...)

 

[egellings]

If you hear a difference it would most likely be noise (hum and/or hiss). But that's tricky because it's the signal-to-noise ratio that's important, and higher gain means more noise and more signal, so if you're just listening to noise higher gain is going to be more noticeable and "worse". So, you have to match the listening volume before comparing noise.

If you do hear noise, the record's surface noise is usually worse anyway. But, it's kinda' nice if you don't hear any noise with the stylus out of the groove. (I don't think I've ever had a phono preamp that didn't have audible noise with headphones, but I'm not 100% sure I don't "play records" anymore.)

There could also be differences in RIAA equalization, but if none of them are terrible you might not notice any difference without careful (level-matched) A/B listening, and that's not easy unless you have two turntables with identical cartridges and two copies of the record... (Or you could make digital recordings to compare.) And if you do hear a difference in EQ you probably won't know which one is right... I once built a phono preamp and it had "enhanced bass" but I didn't know until I compared it to a "proper" phono preamp, and to me mine sounded better!!! (My speakers were probably a little wimpy in the bass.)

But if you are listening to older records their EQ/frequency varies a lot. As with everything else vinyl, the record is the weak link. So if the RIAA EQ (or cartridge frequency response) is not as important as you might think. I assume newer records are better and more consistent but I haven't bought a record since I got my 1st CD player.

It very unlikely that you'd have any audible distortion from the preamp. Again, the record is the weak link.

Deviations from the standard RIAA frequency response curves for vinyl records could also cause sound quality variations.