What is the 'BAT sound'?

Very , very high pitched.

Thanks for the responses. :-)

I'm asking because I'd like to find a preamp that has some midrange bloom without being overly tubey.

I've heard the ARC 3 a while ago (and found it very un-engaging), but I've never heard, say, the VTL 7.5 or BAT 52se or REX.

" I'd like to find a preamp that has some midrange bloom without being overly tubey."

Have you considered Joule-Electra LA-300ME? Harry Pearson wrote that it is most romantic preamp ! (without euphonic coloration) and if you will look for the owners reviews, even here on AudiogoN, you will see that almost everybody state that its most important characterisic is "grabbing" you into the music and not letting you go.

REX by BAT is also excellent preamp but as other noted it has "robust, deeply engaging midrange " - I fully agree. Joule-Electra, on other hand, has nothing robust, nothing specific which bring attention to your ear. One thing - deep involvment with music. Nothing more.

All The Best
Rafael