Trace Acoustic TAB100 Operating Instructions Manual

OPERATING
INSTRUCTIONS

TAB100

INTRODUCTION

The TAB100 is a 100watt combo amplifier that has been specifically designed for the amplification
of the double bass and/or acoustic bass instruments.

All Trace Acoustic Amplifiers are supplied with a moulded mains cable for connecting
power to the mains inlet socket located on the rear panel of the unit.

The Power On/Off Switch is located on the rear panel and fully isolates the Live and
Neutral.

FRONT PANEL CONTROLS

Inputs

The TAB100 has two independent channels to allow a different EQ and gain setting to be achieved
from two separate pickups if required.

Channel 1

Two instrument inputs have been provided on the HIGH Z (high impedance) channel 1 to cope
with the wide variety of different types of acoustic pickup and the equally wide variation in signal
level from different pickup and instrument combinations.

Piezo/Lo Level

The first of these is the PIEZO/LO LEVEL input, which suits any kind of pickup that does not have
its own built in preamp (especially piezo pickups). It has a very high input impedance that gives
excellent results with many types of passive pickup.
This input may also be used with active acoustic guitars that have a low level output signal.

Active/Hi Level

The second input is the ACTIVE/HI LEVEL input; this should be used with instruments or pickups
that produce a high signal output that may overload the PIEZO/LO LEVEL input.

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Input Gain - Signal Level Indication

The GAIN control should be set in conjunction with the SIGNAL LEVEL INDICATING LED. Setting
this control correctly may also influence the decision on which input to use. When correctly set
the amplifier will perform with very little background noise. It is therefore important to set the
gain control correctly using the following procedure:-

1. Plug the instrument into the appropriate input chosen from the previous descriptions.

2. Set the graphic to flat.

3. Play the instrument in the way you wish to use it (e.g. plucked, slapped, bowed, etc.).

4. Increase the GAIN control until the LEVEL INDICATION LED lights up green for most of the
time while playing.

5. Advance the GAIN control further such that on heavy playing the LED changes from green
to red.

6. Decrease the GAIN control slightly to allow a margin of safety.

7. If the LED cannot be made to register red while using the ACTIVE/HI LEVEL input then
transfer your input to the PIEZO/LO LEVEL input and re-adjust the gain, as from 3.

IMPORTANT When correctly set, the green LED should light for most of the playing time.

NOTE As the LEVEL INDICATION LED is driven from after both the GRAPHIC and SHAPE circuits,

it may be necessary to re-adjust the GAIN control once these have been selected/altered.

Hi Trim/Lo Trim

The HI and LO TRIM controls have been provided to “trim” the sound from the user’s
instrument/pickup combinations to achieve a fundamentally flat response prior to any tailoring of
the sound with the graphic of shape facilities.

Channel 2

The channel 2 input operates in exactly the same way as the PIEZO/LO LEVEL input of channel 1.

Input Gain - Signal Level Indication

Set the GAIN control in the same way as channel 1.

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Hi Trim/Lo Trim Channel 2

The HI and LO TRIM controls have been provided to “trim” the sound from the user’s
instrument/pickup combination to achieve a fundamentally flat response prior to any tailoring of
the sound with the graphic or shape facilities.
The HI TRIM controls on CHANNEL 1 and CHANNEL 2 have been set at different frequencies to
allow the two channels to be used for different purposes, e.g. CHANNEL 1 as a “plucked” input
and CHANNEL 2 as a “bowed” input. This arrangement is also useful for treating the outputs of
two independent pickups separately. Some upright bass players prefer to mount a second piezo
pickup under the fingerboard of their instrument to amplify the percussive “slap” produced by
some playing techniques. Channel 2 allows the second pickup’s output to be independently
processed in this situation.

Graphic Equalisation

The five bands of graphic equalisation offered, have their centre frequencies chosen specifically to
suit the acoustic guitar signal and may be used to adjust the sound of the instrument to your
liking.
Avoid extreme settings on any slider as these are unlikely to give any useful results.

Notch Filter

All models in the Trace Acoustic series include a NOTCH FILTER that can be switched IN or OUT.
This is included as an anti-feedback device to allow amplification of an acoustic or double bass
without trouble from feedback caused by the resonance of the body of the instrument.
What is a NOTCH FILTER? Basically, what a NOTCH FILTER does is to remove a very narrow band
of frequencies from the response of the amplifier. If this band of frequencies is narrow enough it
will not be missed from the wide band of frequency response of the unit. This band, of “notch”, is
then made tuneable so that it can be adjusted to the resonant frequency of the body of the bass,
thus reducing the amplification at that particular frequency and eliminating the feedback.
Why is this necessary? Most pickups on an acoustic or double bass are usually mounted on or
near the bridge of the instrument, at the centre of the front of the soundboard. This picks up the
vibration of the strings but also picks up the vibration of the soundboard itself. The soundboard,
being a relatively large area, will also pick up the sound of the speaker. This will be amplified via
the pickup and amplifier and cause feedback to occur at the resonant frequency of the
soundboard.
Each instrument will have its own resonant frequency and it is this frequency that you must
adjust the NOTCH FILTER control to find. The most effective way of doing this is to deaden the
strings of the bass, turn the amplifier up loud until feedback occurs, switch in the NOTCH FILTER
and adjust it until the feedback disappears. This has then set the NOTCH FILTER to your particular
instrument.

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