I'm using right now Ernie Ball Super Slinkys and I find them just a bit too bright for my taste. Are there any nickel rounds which are slightly mellower when they are broken in?
Let them settle and the out of the package zing will go away and it will get warmer. But for a warmer round try a set of those Fender all nickel roundwounds they are quite warm right out of the package. Also they are only 20 dollars!
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Official Fender Precision Bass Club #396
Oh man the zing goes away after a couple of days for me. Have you tried flatwounds? Maybe thats you're answer. If you want to stick with rounds try the fender all nickel not the super bass but the pure nickel roundwound.
Give the EB coated strings a try. They have "bite", but no "zing". It's like they're already broken in to the optimal sound. I'll have to give them awhile to see how they sound, but I think I've found my new favorite string.