These functions complement a third 2-position toggle that gives you a choice of 2 watt or 8 watt operation. Dual inputs and an array of Gain, Treble, Bass, and Master knobs top off the feature set. The amp also sports an “auto aligning” output stage, which automatically adjusts for 8- or 16-ohm speaker loads. The potential downside is that you only get one 14" speaker jack.
Ambitious as the U84-TNT is, it’s an easy amp to get comfy with. Set the Gain switches to their lowest settings, plug into the Lo input—which is still pretty sensitive—crank the Master, and see where things go from there. With a humbucker-loaded guitar, this setup provides good clean response, and has the ability to get reasonably deep into the distortion end of the pool when the Gain is turned up. With single-coils, the same input provides crisp, airy tones at significantly higher settings. Nudging the upper Gain switch to its X2 position (twice the preamp gain) brings a healthy dose of grind that sounds bluesy sweet with humbuckers, but also slicing enough with single-coils to require a severe downward twist of the Treble control. I was never able to get a warm “ooh” thing going with Strats or Teles, but, heck, would you really expect that from an amp with the letters TNT in its name?
Activating the second Gain switch doubles the power amp gain and readjusts the damping. This is like kicking on the afterburner, and the U84-TNT starts showing its explosive side as you wick up the Gain knob. In this mode, the amp rages mightily with humbuckers, and sounds downright toothy and mean with single-coils—think Deep Purple-era Blackmore, but without the blown eardrums. I dig this little maverick’s tightness and aggressive bite, and the fact that it doesn’t go out of its way to be smooth and polite is refreshing, to say the least. The U84-TNT is like a vintage amp in the sense that there’s a “liveness” to it that allows your personality—and that of your guitar—to come though. If you want a small amp that carries a big stick, this little terror definitely warrants an audition.