Stewart MacDonald bomb boost User manual

stewmac.com ©2017 Stewart-MacDonald page 1 of 10
Sheet #i-2151 Updated 1/17
Assembly Instructions
The BOMB BOOST is a classic pedal created by JHS,
makers of high-end effects pedals. Whenever JHS
adds a new pedal to their line, they retire an existing
design. This means great JHS pedals like the BOMB BOOST
have become rare and sought-after. You can’t buy one, but
you can build yourself one—and it’s fun!
This BOMB BOOST KIT is the perfect entry into build-
ing your own pedals: an easy project without many parts.
If you’ve never assembled a pedal before, start right here!
This pedal is a 16dB JFET boost that will push a tube amp into
a clear, natural distortion. Use it in front of your overdrive,
distortion, and fuzz pedals for a thicker, more saturated tone.
Put it after your pedals to maintain your existing tone, but
make it louder (perfect for solos). Or keep it on all the time
to boost signal loss caused by long signal chains or by pedals
that aren’t true bypass.
The original BOMB BOOST was a MINI version, housed in a
mini-sized case. For this kit, we’ve resized the original circuit
to t a standard enclosure.
Easy instructions!
Clear pictures show where
each part goes.
CLASSIC PEDAL KIT
BOMB BOOST
StewMac

stewmac.com ©2017 Stewart-MacDonald page 2 of 10
Tools and supplies
Required: Soldering iron with ne point tip
Solder
Wire cutter/stripper
1/2" nut driver or socket
10mm nut driver or socket
14mm wrench
#1 Phillips screwdriver
Also helpful: Clear silicone adhesive
Circuit card holder
Magnifying glass or OptiVISOR
StewMac Soldering Aids
Power: This pedal requires a standard 9V DC
center-negative power supply (not
included) and consumes less than 100mA.
There’s no battery option.
Tips for soldering
The solder joints you’ll make on the
circuit board are very small, and too
much heat can damage the board.
The idea is to make joints quickly,
without scorching the eyelets.
Hold components in place for soldering by threading the
leads through the board and bending them apart on the
reverse side.
Make your solder joints on the reverse side. Insert the tip into
the eyelet and let it heat for 4-5 seconds before touching it
with solder. This heats the contact enough for the solder to
ow nicely without damage. You don’t need much solder,
just enough to ll the eyelet. After soldering, trim away the
excess lead wire.
Give your pedal a custom paint job!
Any paint sold for use on metal will work well on the kit case.
Spray paints like Rustoleum® or Krylon® are a durable nish.
You might want to paint the case before building the kit,
so you won’t need to take the parts back out for painting.
A way to add custom graphics is to print them from your
computer onto waterslide decal paper. If you use decals,
protect them from scratches by spraying clear topcoats
over them.

stewmac.com ©2017 Stewart-MacDonald page 3 of 10
Parts list
Resistor values are indicated by colored bands, read from left
to right. The rst color in the code is usually the one painted
closest to a lead wire. When a gold or silver band is present,
it’s always one of the last colors in the code. A magnier is
a big help in reading these codes.
#7422 (1) D8 Clear LED (5mm)
#7431 (1) LED mounting bezel (5mm)
#7481 (1) Q1 Transistor (J201)
#7318 (1) Ribbon cable (2")
(6) Lead wires (2")
#7460 (1) DC power connector (21MM)
#1611 (1) Footswitch (3PDT, latching)
#7360 (1) R1 Resistor (5.1 kΩ)
#7365 (1) R2 Resistor (100 kΩ)
#7351 (1) R3 Resistor (47 Ω)
#7357 (1) R4 Resistor (1 kΩ)
#7402 (1) D1 Diode (P6KE12A)
#7311 (1) C1 Capacitor (22 µF)
#7560 (4) Adhesive foam tape
#7456 (1) Volume pot (1 MΩ, linear taper)
#4652 (2) Mono jacks, 1/4"
#7551 (1) Metal case with 4 screws
(1) Circuit board
#7501 (1) Control knob
(Not pictured)
(Not pictured)
Green Brown Black Brown Brown
Brown Black Black Orange Brown
Yellow Purple Black Gold Brown
Brown Black Black Brown Brown
22uF
#7304 (1) C2 Capacitor (.1 µF)
.1J63

stewmac.com ©2017 Stewart-MacDonald page 4 of 10
DC Jack
Mini Bomb
C1
C2
Q1
VOLUME
InJ
D8
S
T
S
T
D1
OutJ
P78869
JHS Pedals Kit
For Stew Mac
R4 Resistor (1 kΩ)
R3 Resistor (47 Ω)
R4
R3
R1
R2
Yellow Purple Black Gold Brown
Brown Black Black Brown Brown
R1 Resistor (5.1 kΩ)
R2 Resistor (100 kΩ)
Green Brown Black Brown Brown
Brown Black Black Orange Brown
Step 1: Install four resistors
Step 2: Install the diode
Resistors have a low prole, sitting closer to the board than taller compo-
nents, so it’s a good idea to install them rst. Their locations are marked with
numbers on the board.
Resistors are not polarized, so it doesn’t matter which lead goes in which
eyelet. They can be installed in either direction.
Diodes are polarized, so they need to be installed in the correct orientation.
Note the stripe around one end: this marks the negative (minus) lead of the
diode. On the circuit board, the printed outline of the diodes also shows this
stripe. Install each diode so that its stripe matches the direction shown on
the circuit board.
Solder D1 in its marked location now.
The leads on diodes sometimes vary in diameter. If the leads don’t t into
the eyelets in the circuit board, trim them at a steep angle to create sharp
points that t into the holes.
JHS Pedals Kit
For Stew Mac
DC Jack
Mini Bomb
C1
C2
Q1
VOLUME
InJ
D8
S
T
S
T
D1
OutJ
P78869
D1Diode (P6KE12A)
R4
R3
R1
R2

stewmac.com ©2017 Stewart-MacDonald page 5 of 10
JHS Pedals Kit
For Stew Mac
DC Jack
Mini Bomb
C1
C2
Q1
VOLUME
InJ
D8
S
T
S
T
R4
R3
R1
R2
D1
OutJ
P78869
Q1Transistor (J201)
.1J63
JHS Pedals Kit
For Stew Mac
DC Jack
Mini Bomb
C1
C2
Q1
VOLUME
InJ
D8
S
T
S
T
R4
R3
R1
R2
D1
OutJ
P78869
R3
R1
R2
C2 Capacitor (.1 µF)
C1 Capacitor (22 µF)
22uF
.1J63
Step 3: Install two capacitors
Step 4: Install the transistor
C1 is a 22 µF polarized capacitor and has to be installed in the right orientation
or it will fail. Note that there is a white stripe running the length of the cap,
identifying the negative (minus) lead. On the circuit board, the circle for this
cap’s location has a thicker line on one side: insert C1 with its stripe facing
that side. (On polarized caps of this type, there’s a second way to identify the
minus lead: it is the shorter of the two leads.)
Solder cap C1 in place.
C2 is a .1 µF cap that is not polarized. Solder it in place facing either direction.
Q1 is a JFET* transistor. It is also directional and needs to be installed in a
specic orientation. Note that Q1 has a at side. On the circuit board, the
location outline also has a at side. Install this transistor to match its outline
on the card.
*JFET: Junction Gate Field-Eect Transistor

stewmac.com ©2017 Stewart-MacDonald page 6 of 10
JHS Pedals Kit
For Stew Mac
DC Jack
Mini Bomb
C1
C2
Q1
VOLUME
InJ
D8
S
T
S
T
R4
R3
R1
R2
D1
OutJ
P78869
.1J63
Footswitch
Ribbon cable
B1M
Step 5: Install the volume pot
Step 6: Install the footswitch, then the ribbon cable
The last component to go onto the circuit board is the volume pot. It installs
on the back of the board. The pot has three connecting lugs; the illustration
in Step 6 shows the pot in position on the board.
The pot has an index pin protruding from the case. Break o this pin before
installation, so the pot will mount ush against the pedal case. Needle nose
pliers work well for removing the pin.
Use the adhesive foam tape to insulate the back of the pot from the sol-
dered leads of the other parts. Solder the pot in place, making sure it sits at
on the back of the board.
Install the footswitch on the back of the circuit board. The switch lugs will
t in only one of two directions; either orientation works ne. Insert the lugs
through the nine eyelets so the switch sits ush, making contact all around.
Solder one lug and let it cool. This holds the switch in place while you solder
the remaining lugs.
Next, install the ribbon cable. Insert the cable leads through the front of the
board, and solder them in place on the back.
Volume pot (1 MΩ, linear taper)
Adhesive foam tape (Goes on back of volume pot)
Break o this index pin.

stewmac.com ©2017 Stewart-MacDonald page 7 of 10
Step 7: Install the lead wires, cut the board
Step 8: Install the LED mounting bezel and the two jacks
Cut the lead wire into six 2" lengths for the input, output, and power jacks.
Strip the insulation on the ends and thread them through the front of the
board. Solder them on the back of the board.
Now you can cut the switch portion of the board away from the main board.
Small wire cutters make quick work of this, and a small saw also works.
LED mounting bezel
Two jacks
Install the plastic mounting bezel for the LED indicator by pressing it in
from the outside, through the top of the case. Spread the tabs open inside
the case to hold it in place.
Install the input and output jacks on the sides of the case. Keep the lugs
facing up so you’ll have easy access when it’s time to solder them.
JHS Pedals Kit
For Stew Mac
DC Jack
Mini Bomb
C1
C2
Q1
VOLUME
InJ
S
T
S
T
R4
R3
R1
R2
D1
OutJ
P78869
D8
.1J63
Lead wire, cut into six 2" lengths

stewmac.com ©2017 Stewart-MacDonald page 8 of 10
JHS Pedals Kit
For Stew Mac
DC Jack
Mini Bomb
C1
C2
Q1
VOLUME
InJ
S
T
S
T
R4
R3
R1
R2
D1
OutJ
P78869
R4
.1J63
D8
D8 LED (5mm)
Step 9: Mount the circuit board in the case
Step 10: Install the LED in the mounting bezel
The main circuit board is held in place by the volume control pot.
Install the pot through the top of the case, and thread the at washer onto
it on the outside. Install the mounting nut so it’s good and snug, but take
care not to overtighten.
Like some of the caps and diodes, the D8 LED (Light Emitting Diode) is
polarized and has to be installed in a specic direction. One side of the diode
has a at edge, indicating the negative lead. Another indication is that the
negative lead is shorter than the positive. The circle marking the D8 location
on the switch circuit board has a corresponding at to indicate the mounting
orientation.
Insert the LED into the bezel. It will be held in place by soldering it to the
switch circuit board in Step 11, but for a more secure mount you can run a
bead of clear silicone adhesive around the LED and bezel.
JHS Pedals Kit
For Stew Mac
DC Jack
Mini Bomb
C1
C2
Q1
VOLUME
InJ
S
T
S
T
R4
R3
R1
R2
D1
OutJ
P78869
R4
.1J63
D8

stewmac.com ©2017 Stewart-MacDonald page 9 of 10
DC power connector Negative Positive
JHS Pedals Kit
For Stew Mac
DC Jack
Mini Bomb
C1
C2
Q1
VOLUME
InJ
S
T
S
T
R4
R3
R1
R2
D1
OutJ
P78869
R4
.1J63
D8
Step 11: Install the footswitch
Step 12: Install the DC power connector
JHS Pedals Kit
For Stew Mac
DC Jack
Mini Bomb
C1
C2
Q1
VOLUME
InJ
S
T
S
T
R4
R3
R1
R2
D1
OutJ
P78869
R4
.1J63
D8
Thread one of the nuts onto the footswitch, leaving
a 1/8" gap between it and the switch housing. Place
the split lock washer on next.
Carefully install the switch so the legs of the diode feed through the D8 holes
on the switch circuit board.
Place the at washer on the switch shaft on the top of the case. As you tighten
the remaining nut on the switch, hold the switch circuit board inside the case
so that it doesn’t rotate.
Solder the D8 LED and trim the leads.
1/8"
Insert the DC power connector so the negative lug is facing up, and tighten
it in place. The negative lug is the one with the largest metal tab.
Solder the installed leads from the circuit board to the jack. Where they attach
to the board, the positive lead is on the the right and the negative is on the left.
This pedal requires a standard 9V DC center-negative power supply (not
included) and consumes less than 100mA.

stewmac.com ©2017 Stewart-MacDonald page 10 of 10
Output
Input
Volume
Adusts the signal’s
overall output level
Requires 9V DC
center-negative power
supply (not included)
Output
Input
Footswitch
On/Off LED Indicator
On/Off
Step 13: Wire the input/output jacks
JHS Pedals Kit
For Stew Mac
DC Jack
Mini Bomb
C1
C2
Q1
VOLUME
InJ
S
T
S
T
R4
R3
R1
R2
D1
OutJ
P78869
R4
.1J63
D8
On the circuit board, the input and output jack leads are labeled InJ and OutJ.
The leads are also labeled Tfor tip, and Sfor sleeve. Looking at a jack, you’ll
see that the sleeve lug is attached to the threaded shaft. The tip lug connects
to the spring metal piece that contacts the tip of a guitar cord.
Solder these four leads as shown to nish the assembly.
Screw the bottom onto the case and put the knob on the volume control.
Plug in and rock out!
Here’s how to use the BOMB BOOST: