Mesa/Boogie Bass 400 Plus Operating Instructions page 4

GROUND SWITCHES
A three-position ground switch is provided to help in reducing buzz originating in the AC
power. It is advisable to leave this toggle switch in the center "OFF" position unless
position A or B reduces buss. With the ground switch in its center position, any residual
shock between the 400 and other equipment (microphones, guitar amps, etc.) cannot
possibly be originating in the Bass 400. Another type of ground switch is located at the
extreme right end of the upper chassis rear. This switch "floats" or isolates the internal
signal ground from the metal chassis. It may be helpful in rack installation, where ground
loops and ground hum might otherwise be caused by contact with rack rails. A safety wire
ground (connecting to the ground pin on the AC mains plug) is internally wired and
remains connected at all times.
FAN SWITCH
Normally the fan should operate at its LOW speed because cooling will be adequate and
dust build-up is minimized. If fan noise is objectionable in a recording studio for example -
you can turn the fan off without causing overheating unless the Bass 400 enclosure is in a
confined space. Use the fan's HIGH speed when the 400 is in an equipment rack with
other units and free air circulation is reduced.
POWER TUBES
The Bass 400 Plus uses twelve MESA 5881 STR-425 power tubes. This massive power
section places very little strain on any individual tube, which allows for tremendous
headroom and greater tube reliability (you'll notice how cool they run). You can expect
about two years of outstanding performance from the tubes; when replacements are
needed, be sure to use only genuine MESA 5881's (available from MESA/Boogie Pro
Centers and Tube Dealers, and from MESA/Boogie directly). The use of other tube
brands will invalidate your Bass 400 Plus warranty! Amplifier bias has been permanently
set at the factory and should never need adjustment.
SPARES KIT
We offer an economical "spare tire set" for the touring professional; it includes a complete
set of replacement tubes, plus spare fuses, knobs, resistors and the like. The whole
package sells for less than the normal price of the tubes alone. Should any problems
occur in your Bass 400 Plus, it is likely that a simple repair using the Spares Kit will have
you up and running in minutes. (Compare that with trying to fix a transistor monster!)
ENJOY!
Most of all, enjoy your music. Your band mates will really appreciate the way your Bass
400 Plus improves the band's overall sound. And you too will enjoy a renewed - and
lasting - burst of playing pleasure. The Bass 400 Plus will give your sound so much more
"punch" and clarity of pitch – especially in conjunction with MESA/Boogie Bass Speaker
Cabinets - that your playing will have far more dramatic impact than ever before!
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