The files for the label are provided in psp, pdf, and jpg
formats. They were made using Paint Shop Pro 6 at 300
dpi and measure 2. 8' H x 5.1" W. I printed multiple copies
of the GTR_Pre-Amp Lbl3M.jpg label and used one for the
drill and filing guide on the enclosure (Figure 4). The
alignment marks should line up with the center of the
dimples in the top cover. I made pencil marks on the rim
to align the label.
I also printed multiple copies of the GTR_Pre-Amp
Lbl3.jpg (Figure 5) for the label itself. After cutting out
the label, I laminated it with Fellows self-adhesive
laminating sheets. After you burnish the laminating sheet
to the label, cut the holes out for the phone jacks,
Next, apply 3M Scotch
removable poster tape to the back
of the label. I placed it around the
outer edges and down the center.
Cut any poster tape that
covers the openings in the label.
Do not peel off the backing from
the poster tape yet. When all the
holes are cut out and you have
dry-fitted the label to the unit to
make sure that all the holes line
up properly, remove the poster
tape backing and carefully align
and mount the label to the enclosure (Figure 6).
Hold the phone jacks inside the enclosure to
prevent them from turning while tightening the control
nut and washer on the label side.
Finish the electrical assembly by connecting some
24 gauge hookup wire from the circuit board to the
input and output phone jacks. Mount the board to the
mounting bosses in the enclosure using small Phillips
head sheet metal screws (Figure 7).
Push the knobs onto the control shafts. I used a 3/8"
drill to remove two of the mounting bosses from the rear
cover so that the quad AA battery pack would fit.
Finally (refer to Figure 8), place the battery holder
over the circuit board with the
batteries facing the board and
secure the bottom cover to the
unit with the four self-tapping
sheet metal screws that are
To use the pre-amp, plug a
1/4" shielded patch cord from your
guitar into the input of the GMPA-
4. Plug another patch cord from
the output of the unit to the input
of an amplifier, PA channel (line
level or low gain), or aux input of a
mixer. The pre-amp works with
most guitar pick-ups, and electret
or high impedance microphones.
For my guitar, I have to set the
treble at about + 6 dB to + 8 dB
( 3 to 4 o’clock), and the bass at
about - 6 dB to - 8 dB ( 10 to 9
o’clock). This gives a very natural,
balanced sound from the house PA
44 November 2013
■ FIGURE 7. PCB installed.
■ FIGURE 8. Final assembly.