I should expand on my comment a little because I have experience with "inexpensive passive preamps", too.
I've experimented quite a bit with passive preamps over the years, and I am a big fan. The first one I built was a simple "pot-in-a-box" affair, and I was immediately struck by how
revealing the thing was; there's a lot to be said for simplifying your signal path as much as possible! I learned that
everything in that path can affect your sound, and that some things have a greater impact than others.
I built a bunch more using various attenuators in different configurations, including the cheapest Radio Shack Alps pot in a shunt-to-ground design in
my $8.01 cigar box preamp. I've used potentiometers from Alps, Apha, Audio Note, Bourns, TKD, and more. I tried the cheap stepped resistor units from China and the good ones from DACT, Goldpoint, Khozmo.
This is an overly broad statement, but pretty much all of the above are better than the standard issue, cheap potentiometer unit found in 99% of the commercial audio gear built today...
But in my opinion, a transformer volume control (TVC) is better than all of the above.
Autoformer Volume Controls (AVCs, or Autoformers) are technically
slightly different than TVCs, but most people lump them in the same category and call them all TVCs. That's fine by me. We could also call them Inductive Volume Controls but that hasn't really caught on...
I've used, built and/or listened to TVC units from Dave Slagle (Intact Audio), Stephens & Billington (S&B), Silk, and Prometheus Audio and they are all really really nice. My favorites thus far are the Slagle and S&B.
I don't pretend to fully understand
why these things sound better, but they do. I think it has to do with reflected impedances and loading of the respective source units. Inductive volume controls present a "friendlier
" load to our source components,
especially at lower volumes, than a resistive element.
My current passive preamp is a DIY affair that I built with Dave Slagle's autoformers in John Chapman's (Bent Audio) packaging. Mine were
silly expensive but the great thing is that you can get the
very same sound from Dave's $200 autoformers as you do from
EMIA's Elmaformer at many multiples the cost.
In my system, TVCs are non-negotiable. Give 'em a whirl -- I think you'll like them, too.