Marshall Amplification VBA400 - Manual (Page 4)

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10. Gain
The VBA400 is an all valve bass head and as
such is ideally suited to creating thick musically
overdriven tones or warm clean tones. If you
require a clean bass sound turn this control up
until your bass just starts to distort and then back
it off slightly. If on the other hand you would
like a distorted sound, simply turn up the Gain
control until the required amount of distortion is
achieved. Another tip, for those of you who
have got active basses who want a distorted
tone, is to try plugging your bass into the Passive
Input. This will cause no harm and may provide
the sound you are looking for.
Tuner Mute
The VBA400 features a Tuner Mute facility. On
the rear panel there is a tuner output, item 1,
which allows you to keep a tuner connected
permanently in-line. By pressing the Tuner
Mute On/Off button, item 12 on the front panel,
you will cut the sound to the speakers and to the
DI output allowing you to tune up in silence.
11. LED
Indicates when the Tuner Mute facility is in use.
12. On/Off
Allows you to switch the Tuner Mute facility on
and off.
Inputs
Though the Passive and Active inputs were
designed around the signal from an active bass
and a passive bass guitar respectively, you
should experiment to see which input best suits
your style. Don’t worry, connecting your bass to
the wrong input will not harm your VBA400 but
may give you the sound that you are trying to
capture.
If you are using a Tuner in-line via item 1 on the
rear panel, you should still use one of these
inputs to connect your bass.
13. Passive
This input is designed to take the signal from a
passive bass. If your bass guitar is passive plug
it in here. We recommend that you always use a
high quality screened cable for this to help
prevent noise, interference and unwanted
feedback.
14. Active
This input is designed to take the signal from an
active bass. If your bass guitar is active plug it
in here. Again we recommend that you always
use a high quality screened cable to help prevent
noise, interference and unwanted feedback.
15. D.I. pre-post selector
The VBA 400 features a D.I. Output, item 5 on
the rear panel, designed for connection to
professional recording or P.A. equipment.
By selecting ‘Pre’, the signal for the DI will be
taken from a point in the signal path before the
front panel controls and will only be affected by
the Tuner Mute, Item 12. This means that you
will have no other influence over your sound
being sent to the external recording or P.A.
equipment connected to the D.I. output socket.
By selecting ‘Post’, the signal for the DI will be
taken after the Gain and Equalisation controls
(but before the master volume control), giving
you tonal and level control over the signal being
sent to the external equipment.
1. Tuner Output
The Tuner Output allows you to keep a tuner in-
line at all times. See Tuner Mute in the Front
panel Functions section for a full overview of
this facility.
Effects Loop
The VBA400 features a series effects loop for
optimum connection of external effects. As this
is a series loop, all of the pre-amp signal is
passed through the loop when in operation and
the blend between ‘dry’ and ‘effects’ is
determined solely by the setting of the ‘mix’
facility on your chosen effects processor.
2. Send
For connection to the input of an external effects
processor.
3. Return
For connection to the output of an external
effects processor.
4. D.I. Normal / Earth Lift
Linking one piece of earthed electrical
equipment to another earthed piece of electrical
equipment can result in an audible hum, due to
the formation of an earth loop. In the past
people would get round this problem by
removing the earth of one of the appliances,
which is of course extremely dangerous. The
VBA400 features an Earth Lift which allows
you to safely ‘lift’ the D.I. signal earth on the
amp, should you be experiencing earth loop hum
problems.
5. D.I. output
The VBA400 features a low impedance,
balanced XLR D.I. Output for connection to
professional recording or P.A. equipment.
See Item 15 on front panel for more details.
6. Impedance Selector
It is imperative that the output impedance
selector on this amplifier matches the impedance
of the speaker(s) that it is driving.
The VBA400 delivers 400 Watts R.M.S. into 2
or 4 Ohms. Both the VBC810 and VBC412
cabinets are 4 Ohm cabinets. Therefore if you
are using one cabinet ensure that the impedance
selector is set to 4 Ohms, and if you are using 2
cabinets ensure that the impedance selector is set
to 2 Ohms.
Failure to do this can result in serious damage to
the amplifier.
7. & 8. Loudspeaker Outputs
For connection to VBC810 and or VBC412
cabinets. See above for impedance details.
Always use short, high quality, heavy duty
speaker leads to connect this amplifier to the
loudspeaker cabinets. Two speaker leads are
supplied with the amplifier for this purpose.
Do not use screened, guitar type, leads.
9. Fan Speed - Low & High
The VBA400 features 12 valves in total, 8 of
which are power valves. Normal air convection
would not be sufficient to keep such an amplifier
cool, and the VBA400 therefore features a fan
which sucks cool air through the front vent and
pushes the resulting warm air out through the
rear vent.
To ensure optimum cooling of the amplifier in
all operating environments, the fan has two
operating speeds, low and high. Low should be
selected for normal operating situations.
However, if this amplifier is going to be used in
close proximity to other units generating
appreciable amounts of heat, or if the ambient
air temperature is high, the higher fan speed
should be selected. The VBA400 features over
temperature protection which will shut the unit
down should internal temperatures become
excessive, due for example to obstructed front or
rear air vents. This protection is self-resetting
after a period of approximately thirty minutes.
10. H.T. Fuse
Always ensure that the correct value fuse is
fitted - see rear panel for details.
If this fuse fails repeatedly, you should refer the
amplifier to a qualified Marshall service agent.
11. L.T. Fuse
Always ensure that the correct value fuse is
fitted - see rear panel for details.
If this fuse fails repeatedly, you must refer the
amplifier to a qualified Marshall service agent.
12. Mains Input
Connects the amplifier to the mains power
supply.
The VBA400 is able to operate on 100, 115 or
230 Volts A.C. (50-60 cycles) by appropriate
selection of internal voltage setting links and
fuse types. Should you require to operate your
VBA400 at a different mains voltage to that
which the unit was originally intended, refer the
amplifier to a qualified Marshall service agent,
who will make the required adjustments.
VBA400 Rear Panel Features (page 26)
Valve Replacement
The valves fitted at the Marshall factory have been extensively tested and selected to ensure close
matching of electrical characteristics, which, in conjunction with the amplifier’s internal bias and balance
controls (which are not user adjustable) should ensure long and reliable operating life.
As with any valve amplifier, the valves (particularly the output valves) do not have an infinite life and will
require replacement at some point. The life expectancy of a set of valves depends on many factors including
how frequently the amplifier is used, the quality of the valves fitted and proper use of the mains and standby
switches when powering the amplifier up and down.
Signs that the valves are nearing the end of their useful operating life include loss of perceived output
power, increase in valve microphony (detectable as a background ‘ringing’ type noise) and deterioration in
tone. When the time comes to fit new valves it is strongly recommended that only Marshall replacement
valves, tested to the same specification as the originals, be used, and that these are installed by an approved
Marshall service agent who has access to the measuring equipment required to set the internal bias and
balance controls to optimally suit the new valves being fitted.