Just a quick report on the recent installation of one of the Classic range (no Z mode switching) in my Letts fretless. [url="http://www.audereaudio.com/Classic2.htm"]http://www.audereaudio.com/Classic2.htm[/url]
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I went for the custom configured option with two stacked knobs, treble/bass EQ and volume/tone. I have to say that I am very happy with the results. The preamp is actually quite subtle which is exactly what I was after. I have landed on boosting the bass by c. 50%, the treble by a bit less (say 25%) and then rolling off the tone just a nadge to keep the overall warmth.
The low end is now much better defined to my ears and the overall sound of the bass hasn't been changed a great deal, just evened out, so very happy with the results. Not the cheapest option I have to say, but in terms of the easy of installation and sound a good buy (imho of course).
I had seriously considered the East BTB but having an active tone on my ACG bass, I really like this feature within the preamp.