Front panel controls – Mesa/Boogie Walk About Bass Amplifier User Manual

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FRONT PANEL CONTROLS:

(Continued)

GAIN:

This control determines the overall character of the input sensitivity. The lower regions of the control (below 12:00) lend

greater headroom and provide a scooped, brighter personality. The upper harmonics come through more prominently in this area of
the control making the top end sound more transparent and sweet. This region is especially useful for funkier stuff when thumbing is

in order. It keeps the rubber- band feel intact in the lows and mids while voicing the snap just
high enough to avoid harshness, or the dreaded “gak” when the G string is plucked.

As the

GAIN control is increased past 12:00 a richer, more “well-rounded” voice becomes

dominant and headroom starts to diminish in increments until eventually, a tube overdrive
sound appears as the 12AX7 input tube is driven into saturation.

The region between 12:00 and 2:30 is where the classic, warm tube sound resides and within
this narrow band you will discover a world of tone. Tiny increments here produce subtle, but
important differences in the attack characteristic which in turn, feel like changes in the time
domain. By experimenting with the amount of gain, you can actually voice the amp to feel as

if it bounces just ahead of the groove - or lays back a little deeper to produce a more Fatback feel. The difference in attack and sustain
produces striking results as to how the bassist - and in fact the whole band - perceives things in the time domain.

BASS:

This control is responsible for the basic mix of low frequencies in the tube pre-amp. As mentioned earlier in the Helpful Hints

section, the

BASS control is an active shelving type as opposed to a passive style control. This means that a center Q point has been

chosen and this control allows you to either boost or cut that frequency. This control differs from the low band of the PARAMETRIC
in that it has a broader Q point with a more gentle ramp as opposed to the PARAMETRIC’S’ narrow Q that is used with a separate
GAIN control.

The

BASS control is actually a gain and frequency control all rolled into one with the Q

center at 55Hz and harmonics in both low and high directions are affected because of its
broader band nature. As the control is increased past 12:00 there is a 6db per octave rise
in gain with the frequency topping out at 321Hz. With 12:00 straight-up representing “ﬂ at”
(a no boost/no cut setting).

As the

BASS control is dialed below 12:00, 55Hz and all associated harmonics are reduced

and eventually notched completely out of the signal. Conversely, there is a 6db per octave
cut beginning at 55Hz going down to 20Hz where the shelving ends with a cut gain of -20db

cut gain

as the control approaches 7:30 (off).

This type of broad band, active rotary control makes it possible to achieve bass characteristics far beyond that of a conventional
passive type control. It can increase the low end to an almost absurd level and with a ﬂ ick of the wrist, dip it to near transistor radio
skinniness. Needless to say, with any control this powerful a certain amount of ﬁ nesse must be applied to achieve musical results. Be
especially mindful of this when using the 3 Band Semi-Parametric in conjunction with the

BASS control.

this narrow band you will discover a world of tone. Tiny increments here produce subtle, but

INSTRUMENT

INPUTS

PASSIVE

ACTIVE

GAIN

BASS

FOUR - STAGE VACUUM TUBE