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With the switch in the
active
position, the preamp presents a lower gain and input impedance which is
tailored to
active pickups.
An
active pickup
is, for all practical discussions, any pickup that uses pre-
amplification between the pickup element and the amplifier input. The purpose of this pre-amplifier is to
buffer the high impedance signal from the pickup element (magnetic, piezo-ceramic, piezo-film etc) and
convert it to a higher level, lower impedance form. It is common for a bass with active pickups to have
higher output level and longer sustain because only a small portion of the energy is required to make the
electrical signal comes from the vibrating string. The majority of the energy comes from an external
power source such as a battery. Additional features may be provided with the active pickup, such as
equalization, volume control and compression.
Input Signal Mute Switch —
The input on the
GBE 400 bass amplifier
includes an “
input mute”
switch. With this switch, you can place the amplifier (and the direct output) in standby mode between
sets without having to change any of your volume settings. This feature is especially handy when using
the tuner output since you will still be able to use your tuner without having sound come from the ampli-
fier or P.A. system. No more re-patching or fumbling in the dark! A red LED turns on when the input
mute is active, reminding you that you are in “stand-by” mode.
Input Gain Control & O/L LED —
The “
input gain”
control, in conjunction with the signal and clip LED,
allows you to adjust the preamp input gain sensitivity to the instrument you are playing. Basses can
have an output level from a few thousandths of a volt to several volts. Generally, you want to see only
an occasional flash of the red clip LED when you really hit the string hard, then adjust the
master volume
control
for playing volume. Distortion of the preamp gain stage will occur when the red clip LED is illumi-
nated, so plan accordingly. The best signal to noise ratio will result with the above method.
Signal Shaping Switches —
There are 3 separate shaping filters on the
GBE 400
. The
“L.F. EXTEND”
lowers the low frequency roll-off response of the preamp (between 30 and 45 Hz) to allow the full effect
of 5+ string and extended scale instruments. The “
MID SCOOP”
function introduces a midrange scoop
at approximately 800 Hz, with a lower “Q” than typical equalization provides. The
“H.F. ATTACK”
func-
tion increases brightness and sparkle (approximately 4KHz) of the signal, allowing exaggeration of per-
cussive effects and string sound.
Active 5 Band Equalization —
The “
active 5 band equalization”
used in the
GBE 400
amplifiers is com-
posed of 1 shelving low frequency control, 3 peaking midrange controls and 1 shelving high frequency
control. These filters are not interactive and are effective as an advanced tone control system. The filters
have a cut/boost range of +/- 12dB and a smooth, musical sounding response.
Low Frequency - 80 Hz
Low-Mid Frequency - 200 Hz
Mid Frequency – 500 Hz
High-Mid Frequency – 1250 Hz
High Frequency - 4000 Hz
Tuner Output Jack —
The “
tuner output jack”
is provided to allow a tuner to remain plugged into the
amplifier while playing. This output remains active when the “
mute switch”
is pressed, allowing for tuning
your instrument while not sending signal to either the “
direct output”
or the speaker. Signal level of -30dB
(typical hot bass level) will drive all known tuners.
Effects Insert Jacks —
The “
effects insert jacks”
are provided to allow access to the pre-equalization
signal for the purpose of inserting signal processing equipment such as compressors, chorus, delay &
reverb processors. “
Send”
(output) and “
return”
(input) are n4 dB level. “Series” devices (such
as compressors and gates) require that the signal flow out from the send jack on the amplifier, through
the processing device and back into the return jack on the amplifier. Parallel or mixed signal devices
(such as chorus, delay and reverb processors) require that the signal flow out of the send jack on the
amplifier, through the unit where it is split into a dry (unaltered) signal and a wet (processed) signal.
