Mod THUNDERDRIVE (K-950) User manual

1Copyright © 2011 by modkitsdiy.com
Use these instructions to learn:
How to build an effects pedal for overdrive.
The Thunderdrive is an overdrive pedal kit that will provide a strong clean signal boost in the early gain
settings and smooth distortion at maximum gain settings. Adjusting output and distortion controls provides
a wide variety of tones in spite of its simple construction. It is capable of overdriving the preamp section of
your guitar amp or adding its own layer of distortion at lower volume.
THE THUNDERDRIVE (K-950)
www.modkitsdiy.com
TO
AMP
IN
FROM
GUITAR
OUT
Unplug when not in use
to save battery life.
OUTPUT DISTORTION
The Thunderdr ve
Modk tsd y.com

TABLE OF CONTENTS
TOO IST …………………………………………………………………………...2
PARTS IST DRAWINGS………………………………………………………….3, 4
SO DERING TIPS …………………………………………………………………...5
STEP BY STEP ASSEMB Y INSTRUCTIONS …………………………………...6
Section 1 – Mount ¼” Jacks and Terminal Strip Components ……………...6
Section 2 – Mount Potentiometers and Footswitch ………………………...7
Section 3 – Mount and Connect Remaining Components ………..…………..7
Section 4 – Wire Remaining Connections ...……………………………...7
ASSEMBLY DRAWIN S (4 Drawings) ……………………………………8, 9
These are the last 2 pages. They should be separated and used as a reference to help
assemble the kit correctly.
2
Visit www.modkitsdiy.com if you have any problems when first turning on your pedal for
troubleshooting help. emember to use caution when applying power to the pedal to avoid electric
shock.
TOOL LIST
Wire Strippers
Needle Nose Pliers
Cutting Pliers
Desoldering Pump
Solder (60/40 rosin core)
Soldering Station
Phillips Head Screwdrivers
Slotted tip screwdrivers (3 mm tip)
Channellock Pliers (or similar type)
uler
Hobby Vise (or other means to secure box while working)

Enclosure
P-H1590BCE (1)
Knob (Scalloped Edge)
P-K801 (2)
Battery Clip
S-H155 (1)
¼” Mono Jack (Output Jack)
W-SC-11-T (1)
¼” Stereo Jack (Input Jack)
W-SC-12B (1)
Stranded Wire (22 AWG) - Blue
S-W22BL (3 FT)
PARTS LIST 1
3
RING LUG
SLEEVE LUG
TIP LUG
GROUND LUG
TIP LUG
250kΩ Potentiometer (Audio Taper)
-VBM-250KA-SS (2)
DPDT Foot Switch
P-H498 (1)
Terminal Strip with 5 Terminals
P-0501H01 (1)
1 2 3
#4 Screw (3/8" long)
S-HS440-38 (1)
#4 Nut
S-HHN440 (1)
#4 Lock Washer
S-HLW4 (1)
3/8" Lock Washer
S-HLW38 (2)

PARTS LIST 2
4
0.1µF Capacitor 50V
C-PFD1-50- (2)
yellow
violet
red
gold
4.7K
4.7kΩ esistor ½ W
-A4D7K (1)
red
black
green
gold
2M
-A2M (1)
2MΩ esistor ½ W
P-QMPSA18 (1)
NPN BJT (MPSA18)
MPS
A18
E B C
1N4148 HIGH SPEED SOLID STATE DIODE
P-Q971 (2)
104J
S-G312
Insulating Tolex
(1)
1"
1 ¾”
(Use to insulate the battery from the footswitch lugs)

SOLDERIN TIPS
1. Bend the component lead
and wrap it around the
connection point.
2. Wrap the component lead
so that it can hold itself to the
connection point.
3. Heat up both component
lead and connection point with
the soldering iron.
4. Apply solder to both
component lead and
connection point.
2. Apply fresh solder to mix in
with old solder joint
1. Heat up old solder joint
with the soldering iron.
3. Use a de-soldering tool to
remove the old solder joint
while it is heated.
De-Soldering Tip
5
It is important to make a good solder joint at each connection point. A cold solder joint is a connection that
may look connected but is actually disconnected or intermittently connected. (A cold solder joint can keep
your project from working.)
Follow these tips to make a good solder joint. Take your time with each connection and make sure that all
components are connected and will remain connected if your project is bumped or shaken.
Bend the component lead or wire ending and wrap it around the connection point.
Make sure it is not too close to a neighboring component which could cause an
unintended connection.
2. Wrap the component lead so that it can hold itself to the connection point.
Touch the soldering iron to both the component lead and the connection point allowing both to
warm up just before applying the solder to them.
Be sure to adequately cover both component lead and connection point with melted solder.
Remove the soldering iron from your work and allow the solder joint to cool. (The
solder joint should be shiny and smooth after solidifying.)
Cut off any excess wire or component leads with cutting pliers.
Clean the soldering iron's tip by wiping it across the wet sponge again after making the
solder joint.

SECTION 1 – Mount ¼” Jacks and Term nal Str p Components
Please refer to DRAWING 1 and DRAWING 2.
Orient the box with ½” hole nearest you.
Mount input jack in 3/8" hole on left side of box with hardware provided.
Mount output jack in 3/8" hole on right side of box with hardware provided.
Mount the terminal strip to the 1/8" hole as shown in drawing 2.
GROUND LUG
TIP LUG
Output Jack
RING LUG
GROUND LUG
TIP LUG
Input Jack
6
Unless noted otherwise, connect and solder all of the following to their respective connection points
as stated. (Make sure none of the component leads are so close together that they could lead to an
unintended connection). Be careful not to overheat the solid state devices (diodes and transistor)
when soldering.
1) Mount one end of the two diodes to terminal #1 on the terminal strip (leaving the other end free
for now). Make sure to connect the diodes with the reverse polarity of one another. In other words,
terminal #1 should be connected to one diode’s cathode as well as the other diode’s anode.
4) Mount the 4.7K resistor to terminals 2 and 5. Do not solder.
2) Strip and tin a 1 ½” piece of wire and connect terminal #1 to #3.
5) Mount the 2M resistor to terminals 4 and 5. Do not solder.
yellow
violet
red
gold
4.7K
red
black
green
gold
2M
3) Mount the MPSA18 transistor to terminals 3, 4 and 5.
Term nals #3: Emitter
Term nals #4: Base
Term nals #5: Collector
MPS
A18
E B C
Washer goes under nut on outside of box. Make sure center “ground” lug of input
jack is facing up. Correct positioning of jack will make soldering connections much
easier. When positioned correctly, tighten nut.
Washer goes under nut on outside of box. Make sure the “tip” lug is on top
(towards the enclosure opening) before tightening nut.
We will refer to terminal numbers from “1” to “5” as illustrated.
Keep the diode leads long so they can reach the volume pot to be mounted later in the instructions.
You might want to connect to the lower terminal holes to leave room for other
components.
Do not solder.
cathodeanode
cathode side is
marked with a
black band
You might find it easier to mount
these diodes by twisting their
leads together first.
1 3

7
SECTION 2 – Mount Potent ometers and Footsw tch
1) Mount the two 250K potentiometers in the 3/8" holes at the top of the enclosure using hardware
provided.
emove nut and flat washer from potentiometers and
place large lock washers (S-HLW38) over shaft of each
pot before inserting them through their mounting holes.
Fasten nut over flat washer and tighten. 1 2 3
1 2 3
Before mounting, gently
bend the pot lugs back so
they are pointing straight
up when mounted.
2) Mount the DPDT footswitch in the ½” hole with its solder lugs oriented as in the drawing.
(The top hex nut and large plastic washer should be fastened on the outside of the box).
Please refer to DRAWING 3.
SECTION 3 – Mount and Connect Rema n ng Components
1) Connect the loose ends of the two diodes to output pot lug “1”. Do not solder.
2) Connect one of the 0.1µF capacitors to output pot lug “1” and terminal #5 of the terminal strip.
Solder all connections at output pot lug “1” and terminal #5 now.
3) Connect the other 0.1µF capacitor to terminal #4 and to both lugs “2” and “3” of the distortion pot.
Solder all connections at terminals #3, #4, #5 and distortion pot lugs “2” and “3” now.
4) Locate the battery clip. Cut 1 ½” length off the ends of each
lead and discard (or save for other projects). Connect the black
lead to the “ring” lug of the input jack. Connect the red lead to
terminal #2 of the terminal strip. Solder these connections now.
Please refer to DRAWING 4.
SECTION 4 – W re Rema n ng Connect ons
1) Strip and tin a 1 ½” piece of wire connect footswitch lugs “3” and “6”.
2) Strip and tin a 1" piece of wire and connect the input jack “tip” lug to the footswitch lug “2”.
3) Strip and tin a 3 ½” piece of wire and connect footswitch lug “1” to distortion pot lug “1”.
4) Strip and tin a 1 ¾” piece of wire and connect the output jack “ground” lug to
output pot lug “3”.
GROUND LUG
TIP LUG
5) Strip and tin a 1 ¼” piece of wire and connect the output jack “tip” lug to
footswitch lug “5”.
6) Strip and tin a 3 ½” piece of wire and connect the output pot lug “2” to footswitch lug “4”.
F n sh t off by double-check ng all of your connect ons, connect and nsert a 9V battery (w th nsulat on), screw
the l d on and fasten the knobs to both pot shafts.
RING LUG
SLEEVE LUG
TIP LUG
Leave the area behind the footswitch free from obstruction because it will be a tight fit for the 9V battery back there.

DRAWING 1
TOP
LEFT SIDE
RIGHT SIDE
1/2"
DRAWING 2
INPUT JACK OUTPUT JACK
1
5
INSIDE VIEW OF THE
ENCLOSURE
1/8"
3/8" 3/8"
MPS
A18
4.7K
2M
8
B
E
C

123
123
DRAWING 3
INPUT JACK OUTPUT JACK
1
5
MPS
A18
4.7K
2M
123
123
INPUT JACK OUTPUT JACK
MPS
A18
4.7K
2M
DRAWING 4
OUTPUT
POT
104J
DISTORTION
POT
104J
BLK
ED
2
3
1
6
5
4
9
1"
1 ¾”
Place the insulating tolex
between the battery and
footswitch lugs “3” and “6”
to prevent shorting the
signal to ground through the
battery case in bypass.