Mod Nexus Series User manual

Seismic Shift JFET Boost
SEISMIC SHIFT
SEISMIC SHIFT
Copyright © 2021 by modelectronics.com
The Seismic Shift is a JFET boost based on one of the earliest effects to ever be
used on stage. This pedal adds subtle color to a guitar's sound while
maintaining the natural tone of the guitar. It packs a serious punch that can cut
through any mix when soloing or whenever some extra “umph” is required. The
Seismic Shift pairs nicely with amps and other pedals. Place it ahead of tubes,
preamps, overdrives, distortions, and fuzz pedals to shift your gear onto a new
level.
The Seismic Shift pedal kit is the introduction to the Nexus Series from Mod
Electronics. This series features a PCB base rather than the Mod Electronics’
traditional point-to-point wiring kits to offer builders an even wider variety of
effects to build. The Seismic Shift kit is designed for all skill sets and is the
perfect first build for those unfamiliar with PCB construction.
The pedal operates on both 9VDC and 18VDC. A center negative power supply
is required for use (not included w/ kit). There is no battery connection. When
using 9VDC the pedal draws 8mA. When using 18VDC the pedal draws 16mA.
The enclosure size is a standard 1590B (4.4" x 2.4" x 1.2").

Table of Contents
Seismic Shift JFET Boost 1
Notes on PCB Construction
Parts Lists
PCB BOM's
Applying The Sticker
Main PCB Construction
3PDT PCB Construction and Enclosure Parts
Calibration
Schematic
2
3-4
5
6
7-9
10-13
14
15
Section Page
Required Tools
Adjustable Wrench
Cutters
Lead Formers
Needlenose Pliers
Phillips Head Screwdriver
Ruler
Small Flat Head Screwdriver
Solder
Soldering Iron
Wire Stripper
Xacto Knife of Similar Cutting Tool
Optional Recommended Tools
Anti Static Wrist Strap
Desoldering Braid
Desoldering Pump
Helping Hands
Multimeter
Oscilloscope
PCB Vise
Signal Generator
Tweezers
For a full-color digital copy of these instructions please visit https://www.modelectronics.com/

Notes on PCB Construction
Seismic Shift JFET Boost 2
Lead Spacing
This section is intended for those unfamiliar with or new to constructing circuit boards.
Components are made in two common mounting types, radial and axial. Radial
components feature leads that are parallel and oriented in the same direction
whereas the leads of axial components protrude from each end of the component
oriented in opposite directions.
These parts will have corresponding footprints on the PCB marked with text.
C_ designates a capacitor and R_ is used for resistors. The BOM (bill of materials)
will cover all of the designators. Each footprint has a specific spacing.
Footprints for the radial parts will match the spacing of that part but axial parts
require preparation to fit. For the resistors in this kit you can simply use your
finger to push the lead until it is perpendicular where the lead meets the part.
Other axial parts will have lead spacing that are referenced in the instructions.
Use a lead former tool on these parts.
Soldering
After inserting the PCB into its footprint make sure that the component is sitting
flush against the PCB. Hold it in place and bend the leads on the opposite side of
the PCB away from the component. This will keep the component flush to the PCB
when soldering.
Make sure your soldering iron is fully warmed up before soldering. Position the
tip of the iron so that it is touching both the solder pad of the PCB and the
lead of the component. Slowly feed solder onto
the pad. The solder should flow evenly across
the pad and will slope up onto the component
lead. You may need to move the end of the solder
strand around the pad to ensure that the pad is fully
coated in solder and that it is also bonding to the lead.
Repeat this process for each lead of the component then
use a pair of cutters to snip the lead directly above the peak
of the solder.
Ideally the solder will flow through the pad hole and a small
amount will reach the opposite side of the PCB. This can
take some practice to master and is not critical. Focus on
consistently achieving full coverage of the pad with slight
slopes surrounding the lead first.

R-N100
Main PCB Parts List
R-N100K
R-N22K
1MΩ1/4W Metal Film Resistor
P-Q1N5817
C-D100N-50
C-D100-3000
C-PEID047-100
C-PEID1-100
P-QPF5102
R-VT96Y-5K
R-VAV-B500K
100Ω1/4W Metal Film Resistor
100KΩ1/4W Metal Film Resistor
R-O1M
22KΩ1/4W Metal Film Resistor
1N5817 Schottky Diode
250uF Electrolytic Capacitor
100nF Film Capacitor
100pF Ceramic Capacitor
47nF Film Capacitor
100nF Ceramic Capacitor
50uF Electrolytic Capacitor
5KΩTrimmer, 3296Y
B500KΩ9mm PCB Mount Potentiometer
PF5102 JFET, N-Channel
C-ET50-50-MOD
C-ET250-25-MOD
Qty 1
Qty 1
Qty 2
Qty 1
Qty 1
Qty 1
Qty 1
Qty 1
Qty 1
Qty 1
Qty 1
Qty 1
Qty 1
Qty 1
K-902-BOARD Seismic Shift Main PCB Qty 1
Seismic Shift JFET Boost 3

P-L352
P-H501-L-BLK
R-N1K
Red 5mm Diffused LED
1KΩ1/4W Metal Film Resistor
Qty 1
Qty 1
Qty 1
P-L710-RED
P-K382B
W-RN-11
Black Skirted Knob with Arrow
Mono 1/4" Jack
Qty 1
Qty 2
Qty 1
S-W3024TC-BK-50 24AWG Stranded Top Coat Wire 3 ft
P-H1590BCE-BK Black 1590B Enclosure Qty 1
P-PC-3PDT-BOARD 3PDT PCB
Soft Click 3PDT Footswitch
Qty 1
3PDT PCB Parts List
Enclosure Parts Lists
Seismic Shift JFET Boost 4
Seismic Shift Sticker
K-902-LABEL Qty 1
Red LED Lens
P-JB-IN-U Low Profile DC Barrel Jack Qty 1

PCB BOM's
Seismic Shift JFET Boost 5
R1
R2
R3
R4
R5
D1
C1
C2
C3
C4
C5
C6
RV1
RV2
Q1
100Ω
100KΩ
1MΩ
22KΩ
100KΩ
1N5817
250uF
100nF
100pF
47nF
100nF
50uF
5KΩ
B500ΩK
PF5102
1/4W Metal Film Resistor
1/4W Metal Film Resistor
1/4W Metal Film Resistor
1/4W Metal Film Resistor
1/4W Metal Film Resistor
Schottky Diode
Electrolytic Capacitor
Ceramic Capacitor
Ceramic Capacitor
Film Capacitor
Film Capacitor
Electrolytic Capacitor
Trimmer, 3296Y
9mm PCB Mount Potentiometer
JFET, N-Channel
Part Value Type
R_LED
LED
Footswitch
1KΩ
Red
3PDT
1/4W Metal Film Resistor
5mm Diffused Red LED
Black Soft Click 3PDT Footswitch
Part Value Type
Seismic Shift PCB
3PDT PCB

Applying The Sticker
Seismic Shift JFET Boost 6
Locate the top of the pedal as well as the top of the sticker.
The cover of the instructions for your kit will have an image of
the pedal that can be used for reference.
Peel the backing from the sticker. Carefully line up the top
edge of the sticker with the top of the pedal. Try to line up the
center of the circles to the center of the potentiometer hole.
Press down to apply the sticker only to the edge. Run a finger
across the edge to push any air out from beneath the sticker.
Continue this motion as you work your way down the pedal
until the sticker is fully attached.
Locate the holes beneath
the sticker and depress
them using a fingertip. Be
sure that the area of the
sticker surrounding the
holes is fully adhered to
the surface.
With an Xacto knife or
similar tool, carefully
pierce the sticker in the
center of each hole.
Carefully work the knife
from the center of the
hole to the edge and begin
cutting fully around the
edge until the sticker has
been fully cleared from
the hole.

Main PCB Construction
Seismic Shift JFET Boost 7
Part 1: Resistors
Locate the Seismic Shift Main PCB. The following steps will cover the placement and soldering of all
parts that are mounted on this PCB. Use the BOM and Parts List as references.
Locate the 100Ωresistor. Its color bands are brown, black, black, black,
brown. Insert and solder this resistor at R1.
Locate one of the two 100KΩresistors. Their color bands are brown, black,
black, orange, brown. Insert and solder this resistor at R2.
Locate the 1MΩresistor. Its color bands are brown, black, black, yellow,
brown. Insert and solder this resistor at R3.
Locate the 22KΩresistor. Its color bands are red, red, black, red, brown.
Insert and solder this resistor at R4.
Locate the remaining 100KΩresistor. Insert and solder at R5.

Main PCB Construction
Seismic Shift JFET Boost 8
Part 2: Solid State Components
Locate the 1N5817 diode. When inserting the diode, note the orientation
of the band. This should match the orientation on the silkscreen. Use the
.4 notch on the lead formers. Insert and solder this diode at D1.
Locate the PF5102 JFET. When placing the JFET, note the orientation of
the flatted side. This should match the orientation on the silkscreen.
Take extra care to avoid bridging the solder pads. Begin with the middle
pad first then solder the two outside pads. Insert and solder this JFET at
Q1.
Part 3: Axial Capacitors
Locate the 250uF electrolytic capacitor. When inserting the capacitor, note
the orientation of the positive lead. This should match the orientation on
the silkscreen. Use the 1.0 notch on the lead formers. Insert and solder
this capacitor at C1.
Part 4: Radial Capacitors
Locate the 100nF ceramic capacitor. This is the circular capacitor marked
104. Insert and solder this capacitor at C2.
Locate the 50uF electrolytic capacitor. When inserting the capacitor, note
the orientation of the positive lead. This should match the orientation on
the silkscreen. Use the .8 notch on the lead formers. Insert and solder
this capacitor at C6.

Main PCB Construction
Seismic Shift JFET Boost 9
Part 4: Radial Capacitors (cont.)
Locate the 100pF ceramic capacitor. This is the circular capacitor marked
101. Insert and solder this capacitor at C3.
Locate the 47nF film capacitor. This is the rectangular capacitor marked
473. Insert and solder this capacitor at C4.
Part 5: Potentiometers
Locate the 5KΩ3296Y 25-turn trimmer. Insert and solder this trimmer at
RV1.
Locate the 100nF film capacitor. This is the rectangular capacitor marked
104. Insert and solder this capacitor at C5.
Locate the B500KΩ9mm potentiometer. Flip the PCB to show Side 2.
When inserting the potentiometer, make sure that the two outside
brackets are fully inserted and that the standoffs are flush with the PCB.
Make sure the Q1 leads are neatly soldered and trimmed before placing.
Insert and solder the potentiometer at RV2.

3PDT PCB Construction and Enclosure Parts
Seismic Shift JFET Boost 10
Part 1: Board-Mounted Components
Locate the 3PDT PCB. The following steps will cover the placement and soldering of all
parts that are mounted on this PCB. Use the BOM and Parts List as references.
Locate the 1KΩresistor. Its color bands are brown, black, black, brown,
brown. Insert and solder this resistor at R_LED.
Locate the 3PDT footswitch. Flip the pcb to show side 2 and insert the footswitch
into the 9 pin footprint. Solder all 9 pins to the PCB.
Locate the 24AWG stranded wire. Cut the following lengths and strip
the ends of each wire.
-Four 1 3/4" lengths
-Four 2 1/4" lengths
-Two 6" lengths
Part 2: Wire Preparation
Take the two 6" lengths of wire and insert them through side two of the
PCB at the POWER GND and POWER V+ holes. Solder the two wires to the
PCB.
Take the four 2 1/4" lengths of wire and insert them through side one of the PCB
at the PCB IN, PCB OUT, PCB GND, and PCB V+
holes. Solder the four wires to the PCB.

3PDT PCB Construction and Enclosure Parts (cont.)
Seismic Shift JFET Boost 11
Locate the two 1/4" jacks. Solder the four 1 3/4" wires to the sleeve and tip of
each jack.
Locate the red LED, the lens, and 1590B enclosure. Insert the LED
lens into the small hole directly above the large footswitch hole.
Some force may be required. Slide the LED into the lens. The LED
will lightly snap into place when fully inserted. Orient the LED so
that the positive lead (longer lead) is on the left side of the
enclosure and the negative lead (shorter lead) is on the right side
when viewed from below.
Part 3: Mounting to the Enclosure
Remove the mounting hardware from the 3PDT footswitch except
for the serrated lock washer and chrome nut. Make sure that the
chrome nut is threaded to the bottom of the footswitch bushing.
Carefully guide the LED leads through the LED + and LED - holes
while inserting the footswitch bushing through the footswitch
mounting hole at the bottom of the enclosure. The positive lead
goes through the LED + hole and the negative lead goes through
the LED - hole. When fully inserted slide the black metal flat
washer over the bushing of the footswitch
then use the black nut to secure the
footswitch to the chassis. Once
secured, check to make sure the
LED leads are straight, that
the LED is fully inserted into
the lens and that the lens is
flush to the exterior of the enclosure.
Solder the LED to the PCB.

3PDT PCB Construction and Enclosure Parts (cont.)
Seismic Shift JFET Boost 12
Locate the DC jack and mount it in the hole on the top side of the
enclosure. Run the two 6" wires connected to the POWER GND
and POWER V+ along the bottom left edge inside the enclosure
then connect the V+ wire to the longer lug and the GND wire to
the shorter lug. Solder both lugs.
Locate the two 1/4" jacks. Remove the nut and washer from each
jack. Lift the PCB wires (IN, OUT, GND, and V+) away from the
chassis so the two 1/4" jack mounting holes on the left and right
sides of the chassis are easily accessed. Insert the jacks in each
hole as shown to the right. Make sure that the POWER GND and
POWER V+ wires connected to the DC jack are tucked beneath
the left 1/4" jack. Slide the washer over the bushing and secure
each jack with its nut. Check to make sure that the lower lug of
each jack is not touching against the chassis. If so, slightly rotate
the jack until it is fully clear of the chassis.
Using needle nose pliers:
‣Take the wire connected to the lower lug of the left jack (sleeve)
and push it up through the IN JACK GND hole on the 3PDT PCB.
Solder this wire onto the PCB.
‣Take the wire connected to the upper lug of the left jack (tip)
and push it up through the IN JACK IN hole on the 3PDT PCB.
Solder this wire onto the PCB.
‣Take the wire connected to the lower lug of the right jack
(tip) and push it up through the OUT JACK OUT hole on the
3PDT PCB. Solder this wire onto the PCB.
‣Take the wire connected to the upper lug of the right jack
(sleeve) and push it up through the OUT JACK GND hole on the
3PDT PCB. Solder this wire to the PCB.

3PDT PCB Construction and Enclosure Parts (cont.)
Seismic Shift JFET Boost 13
Once the last four wires have been soldered, the main PCB can be
mounted. Insert the potentiometer through the hole towards the
top of the enclosure. If the longer lug of the DC jack is obstructing
the main PCB, bend it away from the shorter lug of the DC jack
until the main PCB can clear it. Slide the flat washer over the
bushing and secure the pot with its nut. Make sure that the four
wires connecting the two PCB's are positioned up and over the
right 1/4" jack.
The pedal is nearly complete. Secure the knob to the pot's shaft.
If installed correctly, the min and max rotational point of the
knob should line up with the edges of the red triangular section.
Leave the back plate offfor now since the trimmer still needs to
be calibrated.
Remove the nut and washer from the 9mm pot mounted to the main PCB.
Grip the small metal tab with a pair of pliers and gently rock the tab until it
snaps off.
Part 4: Mounting The Main PCB
Before mounting the main PCB to the chassis connect the four remaining
wires from the 3PDT PCB through side 1 of the main PCB.
‣PCB V+ connects to V+ on the main PCB.
‣PCB GND connects to GND on the main PCB.
‣PCB OUT connects to OUT on the main PCB.
‣PCB IN connects to IN on the main PCB.
Make sure that each wire is connecting straight across for each connection
as shown in the image below. Solder the four wires to the main PCB.
FULLY COUNTER-CLOCKWISE FULLY CLOCKWISE

Calibration
Seismic Shift JFET Boost 14
Locate the 5KΩtrimmer on the main PCB. With a small flat head
screwdriver rotate the trimmer fully clockwise. This is a 25 turn
trimmer. A quiet clicking sound will occur once the end has been
reached.
Calibrating By Ear
Plug a guitar into the pedal's input and connect the output to an
amp or other device for listening. Plug a 9VDC center negative
power supply into the DC jack. Engage the effect with the
footswitch and set the volume knob for a clean sound. Avoid
overdriving the amp with the pedal. You may need to lower the
volume knob during the calibration process to avoid clipping or
overdriving in the amp.
Strum an open string and begin adjusting the trimmer
counter-clockwise. Try to keep a consistent volume with your
strumming hand. As the trimmer is rotated counter-clockwise
the volume will slowly increase in the pedal.
Keep rotating until the volume begins to decrease. Once the decrease occurs, start rotating the
trimmer clockwise and try to dial in the loudest clean signal. This does not need to be exact and if
you prefer the sound in one direction or the other feel free to leave it as is. The pedal cannot be
harmed by setting the bias differently than intended.
Adjusting the trimmer using an oscilloscope and signal generator will
follow a similar procedure as tuning by ear. Send a sine wave to the input
of the pedal. Make sure the signal is low enough to not cause clipping in
the pedal. ~50mV RMS works well. Attach the oscilloscope to the pedal's
output.
Set the trimmer to the fully clockwise position. Connect the power supply
and engage the effect with the footswitch. Adjust the volume knob and
oscilloscope to get a stable image of the waveform.
The signal should look similar to the image in fig. 1. This means that the
bias is too low. Adjust the trimmer counter-clockwise until it reaches a
near-perfect sine wave like fig. 2. This will coincide with the largest peak to
peak setting for the trimmer. If the signal begins to look like fig. 3, the bias
is too high and the trimmer should be rotated clockwise.
Calibrating w/ Scope and Signal Generator
FIG. 1
FIG. 2
FIG. 3

D1
1N5817
R1
100
C1
250uF
C2
100nF
R4
22K
C5
100nF
V+
R2
100K
C3
100pF
C4
47nF
R3
1M
RV1
5K
Q1
PF5102
500K
RV2
C6
50uF
R5
100K
OUT
1
3
2
1
2
3
IN
3
2
1
GND
V+
OUT
IN
COPYRIGHT © 2021 BY MODELECTRONICS.COM
Seismic Shift (K-902)
Main PCB Schematic