[quote name='Matte_black' timestamp='1435175468' post='2806307']
On those amps the DI probably goes thru the transformer?
Anyway, I think the ABM 500 is already very "boomy" and "wooly", no idea about how that preamp would work with a tube power stage.
I have the 427 myself but it's got a Bassman-style tube preamp. Otherwise, I wouldn't have bought it.
The power stage makes a big difference, though. Expecially on dynamics. You dig into the strings, the amp gives it back - more than on SS amps.
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I think the BTA power stage has more bite and zing to it actually, the ABM stage feels like it has a softer transient response. The BTA is the best bass amp I've ever used, just damn big and heavy...!