I've not found tube preamps to have a sound. Those are wide band enough, and clean enough unless a broken design they don't color the result.
I can see the logic there. Frankly, the idea that tube preamps would have a "tube" sound has always seemed less plausible to me than tube amps (for reasons you've given).
Nonetheless I have had strong impressions that the various tube preamps I owned had different "tubey" sounds. So for instance with my CJ Premier 16LS2 tube preamp: it's common among reviewers and tube amp fans to hold that CJ's amplification has become more neutral sounding over the years, but in their classic hey-day CJ was known for a "golden glow" or "bronze glow" or "caramel tone" to the sound, a sort of upper midrange/lower treble bloom or glow, along with a richness to the sound.
My Premier 16 preamp comes from that purported CJ era and that is precisely what I feel I've always heard from the pre-amp: along with a slight thickening of the sound and addition of "body" often associated with "tubes" it seemed to have this upper mid "glow" or texture that "lightened up" the sound and made the sound more texturally, tonally 'present' a bit less 'stuck in the recording.' Every time I ever took the CJ preamp out of the system either to drive my amps directly from a DAC or to compared it to an SS preamp, exactly those features would seem to come and go with the CJ preamp.
When I got the Benchmark preamp I was able to match levels and spend weeks going back and forth between the signal going through the CJ preamp or going straight through the benchmark preamp, with the click of my remote button. The sonic impressions above where solid and reliable. But of course knowing about bias effects I got around to blind testing between the two (much easier for the preamp vs my tube amps):
Hey folks, I thought I'd post about a little blind test I did between my two current preamplifiers: Benchmark LA4 vs. Conrad Johnson Premier 16LS2 tube preamplifier. People are familiar with the Benchmark LA4 I'm sure: https://benchmarkmedia.com/products/benchmark-la4-line-amplifier A...
www.audiosciencereview.com
Even when I didn't know which preamp I was listening to, it was exactly the characteristics described above - the classic "CJ tube sound" -that seemed to allow me to easily identify the CJ vs the Benchmark preamp. Not that it will convince skeptics - this was mostly for my own interest, but I found it pretty compelling.
That Tube sound is a myth!
See above