Bass 400 Plus
The Spirit of Art in Technology
CONGRATULATIONS! You've just become the proud owner of the world's finest bass
amplifier. When people come up to compliment you on your tone, you can smile
knowingly... and hopefully you'll tell them a little about us! This amplifier has been
designed, refined, constructed and tested to deliver maximum musical performance of any
style, in any situation. And it is very easy to operate.
The idea behind this amplifier is to assemble all the elements of a custom rack system
into one perfectly matched unit. Your Bass 400 Plus includes two separate (and slightly
different) bass preamps, plus a versatile tone control network, an adjustable Effects Loop,
a seven-band Graphic Equalizer, and special driver and buffer circuits feeding a highly
dynamic, twelve-tube power amplifier. All were created especially for bass.
Most musicians know that tube amps are unbeatable for guitar… but what about bass?
Isn't it better to have a big, clean, high-power transistor amplifier? We don't think so. And
our proof is that your Bass 400 Plus will offer superior tone and more usable power than
solid-state systems costing two to three times as much! In our years of research we have
made some surprising discoveries: the best sounding power amplifier for bass is quite
different than the one we use for guitar. And is very different than the best power designs
for keyboard or stereo fidelity. Transistor systems are designed primarily for "laboratory
conditions", not the real world of live music. Your Bass 400 Plus will demonstrate the big
difference: you'll hear knockout punch (without the farting attack) and clear, distinct pitch
(without boominess or mud).
Input 1 and Volume 1 offer a high-headroom preamp that you might find preferable for
active type basses. The gain is slightly lower than Channel 2 and the tonal personality is
slightly different. The Pull Bright switch built into Volume 1 can be great for funk bass, as it
accentuates the harmonics above the Treble control region.
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Input 2 and Volume 2 recreate the classic sounds of the D-180, predecessor to your Bass
400. The gain is slightly higher and may be better suited for traditional basses than
Channel One. But be certain to sample both channels because their tonal personalities
are both very usable with very interesting differences. It is even possible to preset the two
channels and footswitch between them using our separate A-B Footswitch Box.
The Bass 400 Plus uses traditional type tone controls which have been especially tailored
for bass, and whose ranges can be extended by use of the “Pull Shift” switches. The
Treble control, when set high, becomes the most powerful of the three. At settings of 7
and above it will minimize the effect of the Bass and Middle, but they will become the
stronger controls when the Treble is below 5. Most players find a “sweet spot” between 2
and 5 where the tonal balance is just right for them. Pulling out the Treble Shift alters its
frequency center-point downward, toward the upper mid-range. (And since there is more
musical energy at these frequencies, your amp will seem to get a little louder as well.)
Using either Bright switch injects an extra dose of high treble. The Bass control is
wide-ranging and using the Pull Shift can boost its power. Your Bass 400 Plus (especially
when used with our speaker cabinets) can produce more true fundamental tone than just
about anything else. Its bottom-end response is truly "profound" and yet it avoids
boominess and muddiness. The Middle control is the subtlest of the three. Its purpose is
filling the gap between the treble and bass frequencies. Spice according to your liking.
The Master control comes after the Effects Loops and after the Graphic Equalizer. So its
best use is as a sensitivity control for the Effects Return and/or the power amplifier
section. Full undistorted power is developed at settings around 5. There is rarely any
reason to run the Master above 6 or 7, as higher settings merely increase noise without
improving power or tone.
Two pairs of Send and Return jacks are provided; one on the front and one on the rear of
your Bass 400 Plus. So whether you use effects devices on the floor or in a rack, patching
with your Bass 400 is clean and professional. A unique Blend control located on the upper
rear amplifier chassis (where it won't get broken or damaged) enables you to mix “dry”
and effected signals. With the Blend control at 10, all signals will pass through the
accessory effects. Set at 0, the Effects Loop is fully bypassed, as it should be when no
effects are used. Most players find an ideal setting between 2 and 5.
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The Effects Return jack can also be used to plug directly into the 400's power section. The
Master can regulate sensitivity, and the Graphic EQ will be functional. If you wish to use
only the preamp section of your Bass 400, you can use the Effects Send jack as a preamp
output; be sure to set the Effects Blend at 10 and the Master to 0. This will prevent signal
from driving the power section, so running the amp without a speaker or load resistor will
be OK.
Two 8-ohm, two 4-ohm and 2-ohm speaker jacks are provided on the Bass 400 Plus. The
amp will produce its full power at all of these impedances, provided that the total
impedance of your speaker cabinets is matched to the output(s) used. (Slight mismatches
are not a major problem, but they will cause slightly lower output and may shorten tube
life.) When using more than one speaker cabinet, remember that the total load impedance
goes down as more cabinets are connected. For example, if you use one 8-ohm speaker
cabinet, use one of the 8-ohm jacks. But if you use two 8-ohm cabinets, they will be
operating in parallel and the total load will be 4 ohms. Therefore, plug each cabinet into a
4-ohm jack. If you want to use two 2x15 cabinets where each cabinet is rated at 4 ohms
(which is how Boogie 2X15’s are wired), connect both cabinets to the 2-ohm Jacks
The Slave system is an adjustable Direct Output that can be used to feed a mixing board
or another power amplifier. The signal is taken right from the output transformer where the
tone is best and loading problems are avoided. When using the Slave, be sure to first get
the desired sound on the Bass 400 with the Slave Level at zero. Then turn up the Slave
Level until the proper output level is achieved.
A three-pin male XLR jack is provided for connecting to the balanced 600ohm
transformer. Again, the signal is taken from the speaker jack for best results. This output
has a fixed level of about 2 volts peak-to-peak (when the Bass 400 is at clipping level). It
is therefore suitable for either “mic” or “line” inputs on a mixer, although line-level would
be preferable. When using either the Slave or the Balanced XLR output, it is important
that a speaker (or suitable load resistor) be used.
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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.
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.
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.
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!)
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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