This is one of the best bass preamps ever made in my opinion. Its tone is surprisingly true and uncolored, but is able to get a fatter, tubier, growlier, SVT sort of sound compared to the studio cleanliness of the DB-680. It has more low mid punch and growl compared to the slightly scooped and dry mids of the DB-680. The lows also seem more extended than the tight bottom of the DB-680. The top end also has a bit more sparkle to it in the 8k+ region.
Compared to the other makers, no one even comes close. Everything with a Fender tone stack sounds scooped and muddy in comparison. Demeters have as much detail, but lack the low end muscle. The Kern is close, but lacks the clarity. Pretty much the same goes for all of the Ampeg offerings, too. The only pre's I have heard come close are high end recording studio channel strips like UA's and Millenium's.
The EQ is somewhat limited, though. The Bass and Treble affect a very wide bandwidth. The mid is pretty timid and adds more harmonic content than actual mid boost. These attributes leave little for actual scuplting, and are more for subtle alterations. But, the tone doesn't need much fixing if you like what you are putting in to it. The stock tubes are pretty crummy, so swapping in high quality NOS or Reissues is recommended. I like the Mullard and Tung Sol reissues personnally. Overall build quality is typical Aguilar; its a tank.