Warm, yet detailed tube preamp

I’ll add a +1 to look at Don sachs. I have his model 2 and it’s outstanding. I prefer a more neutral sound and so I am running this with the provided rectifier tube; however experimenting with Mullard GZ34 gave exactly the warmer detailed sound you are asking about.  But given your price point you are right at the Raven cost point which is noted to be even more special.

I have Zu Omen Defs also, along with an RP1 (RCA Cleartops).I feel the Rogue with those particular tubes has just the right touch of warmth. It replaced an LTA MZ2 which was not warm at all no matter what tubes were tried,but was very transparent and clear.I enjoyed it more as a 1watt power amplifier.The only fault I find with the RP1 is the volume control - not enough steps to fine tune it just right.I owned a Conrad Johnson PL10 in the past that I wish I'd hung on to sometimes. If I upgrade someday I would have CJ on my short list.

I agree with inna the Vac preamp would be worth your consideration.

Another vote for a Don Sachs pre. Another one that comes to mind is a CJ Premiere 17LS II.

Backert represents a value and sound way above its price point. I’ve never been happier with a hifi component. It’s a lifetime preamp and I recommend it fervently!