Lithium Grim OmniRat Instruction Manual

OmniRat
Building instructions
v1.0

OmniRat v1.0
Manufacturers and product names are mentioned solely for circuit identification, and where applicable their trademarks are the
property of their respective owners who are in no way associated or affiliated with the author. No cooperation or endorsement
is implied.
2
Table of contents
PCB layout ............................................................................................................................................... 3
Components ............................................................................................................................................ 4
Configurations..................................................................................................................................... 4
Build sequence ........................................................................................................................................ 5
Off board wiring ...................................................................................................................................... 6
Potentiometers.................................................................................................................................... 6
Diode Switch........................................................................................................................................ 6
Modifications........................................................................................................................................... 7
OpAmp................................................................................................................................................. 7
Drill instructions ...................................................................................................................................... 8
Troubleshooting ...................................................................................................................................... 8
Schematic ................................................................................................................................................ 9
Read this entire manual thoroughly before you start building the effect! There are some available
options and you should choose which one you want to incorporate before starting your build.
Last update: 17-07-2019

OmniRat v1.0
Manufacturers and product names are mentioned solely for circuit identification, and where applicable their trademarks are the
property of their respective owners who are in no way associated or affiliated with the author. No cooperation or endorsement
is implied.
3
PCB layout
Dimensions: 49,5 mm x 38 mm
1.95 inch x 1.50 inch

OmniRat v1.0
Manufacturers and product names are mentioned solely for circuit identification, and where applicable their trademarks are the
property of their respective owners who are in no way associated or affiliated with the author. No cooperation or endorsement
is implied.
4
Components
Part
Value
Type
Part
Value
Type
C1
22n
MKT
R1
**
1% metal film
C2
4u7
Electrolytic 25V+
R2
560R
1% metal film
C3
2u2
Electrolytic 25V+
R3
**
1% metal film
C4
1n
MKT
R4
1k
1% metal film
C5
100p
MLCC/Silver Mica
R5
47R
1% metal film
C6
**
MLCC/Silver Mica
R6
1k
1% metal film
C7
4u7
Electrolytic 25V+
R7
**
1% metal film
C8
**
MKT
R8
**
1% metal film
C9
22n
MKT
R9
**
1% metal film
C10
**
Electrolytic
25V+/MKT
R10
10k
1% metal film
C11
1u
Electrolytic 25V+
R11
**
1% metal film
C12
100u
Electrolytic 25V+
R12
**
1% metal film
C13
10n
MKT
R13
100k
1% metal film
D1
**
R14
100k
1% metal film
D2
**
P1
**
Distortion
D3
**
P2
A100k
Filter/Tone
D4
**
P3
A100k
Volume
D5
1N4001
Q1
2N5458
IC1
**
VR1
10k
Bourns 3386
Optional diode switch SW1 SPDT (On-On)
MKT can also be FKS, SMF or even greenies.
Configurations
Early Big
Box RAT
RAT
Chinese
RAT2
RAT2
Turbo
RAT
Vintage RAT
You Dirty
RAT
C6
33p
30p
30p
30p
30p
30p
30p
C8
3n
3n3
2n7
3n3
3n3
3n3
3n3
C10
1u
1u
10u
10u
10u
1u
10u (?)
D1-D2
1N914
1N914
1N4148
1N4148
LED
1N4148
1N34A
IC1
LM308N
LM308N
LM308N
LM308 / OP07
OP07
LM308N / OP07
OP07
R1
x
x
2M2
2M2
2M2
x
x
R3
1M
1M
2M2
2M2
2M2
1M
1M
R7
1k5
1k6
1k6
1k6
1k6
1k6
1k6
R8
x
x
x
x
2M2
x
x
R9
1M
1M
1M
1M
2M2
1M
1M
R11
x
x
10k
10k
10k
x
x
R12
47R
47R
47R or 100R
47R or 100R
47R
47R
47R
P1
A150k
A100k
A100k
A100k
A100k
A100k
A100k

OmniRat v1.0
Manufacturers and product names are mentioned solely for circuit identification, and where applicable their trademarks are the
property of their respective owners who are in no way associated or affiliated with the author. No cooperation or endorsement
is implied.
5
Build sequence
Before starting with this section, make sure you have read the configurations section first!
Soldering this board can be very complicated for some people since the solder pads are very close
together. Use a magnifying glass to make the job easier.
The trick to soldering a PCB is to work from small to big components. My building sequence
suggestions in this section are based on the parts I used myself. Sometimes some components are
smaller (or bigger) so always use your own common sense and change the order accordingly. Usually
capacitors can differ a lot in size depending on their rating and value.
Note: Do not blow on your solder in an attempt to cool it down. That can result in a bad join that
might corrode! Also take extra care not to short components.
Start by soldering the jumpers (if applicable) , resistors and small diodes (not LEDs if used). If needed
you can create a jumper using a spare piece of lead from a resistor or diode.
If you want to experiment with another transistor for Q1 then you could socket it instead of soldering
it to the board. You’ll need a some 20 SIL sockets, break off the 3 pin socket and solder it to the
board. Now is the time to solder this socket on the PCB as well as the socket for the IC. Place the
transistors and IC once you are finished with all soldering and off board wiring!
Now continue by soldering the MLCC, small SMF/MKT/Wima capacitors then solder the internal trim
pot (VR1). Now finish by soldering the transistors (if not socketed), the bigger SMF/MKT/WIMA and
the electrolytic capacitors.
I suggest you now drill the holes in your enclosure so you can use it during the off board wiring. This
PCB is very sensitive to noise! Prevent crossing input and output wires and keep the wires as short as
possible (and/or use shielding on the input and output).
Besides the components mentioned in the components table, you will need:
•1 stereo input kack and 1 mono output jack.
•2,1mm DC jack (isolated).
•22 gage stranded hook-up wire.
•LED holder. This enables you to mount the LEDs in the enclosure.
•Footswitch 3PDT (9 pins)
•Hammond 1590B or 125B style case (or similar) in your favorite color. You can of course
experiment with other enclosures, but measure twice before you start drilling!

OmniRat v1.0
Manufacturers and product names are mentioned solely for circuit identification, and where applicable their trademarks are the
property of their respective owners who are in no way associated or affiliated with the author. No cooperation or endorsement
is implied.
6
Off board wiring
Potentiometers
In the pictures below you see the correct pin numbering of the pots (Alpha 16mm style).
Solder the wires accordingly and it is always a good idea to twist the wires together to create some
extra shielding against external noise. The rectangle pad marks pin 1.
You can break off the pin I marked with the yellow circle with a small pair of pliers.
Note that the Tone/Filter pot is wired different on early RATs vs later RATs. So there is no actual right
or wrong way to wire it. If you do not like the orientation in this version you can reverse the PCB
mounted pot or use a reverse wired Alpha pot with solder lugs (like in the picture above).
Diode Switch
The wiring for the switch is the same as for potentiometers, marking pin 1 with a rectangle pad.
There is no wrong way to wire it as long as the pad of pin 2 is connected to the middle lug of the
SPDT switch.
The optional diode switch (SW1) enables you to switch between 2 sets of diodes. You could choose
to equip D1 and D2 with the correct set of diodes per your chosen configuration and use D3 and D4
to experiment with your own configuration. As the 1N4148 and 1N914 are almost identical, I suggest
you use 3 mm LEDs for D3 and D4, but of course you are free to choose different. D1 and D2 are
designed to fit almost all types of diodes, but D3 and D4 are designed for LEDs. If you want to use
other diodes in those positions, you will have to mount them upright.
VR1 is a so called Warp control as described by AMZfx. This control is used to change the harmonic
content of the clipped output from primarily odd harmonics to a mixture of even and odd harmonics.
If you do not want to use it you can leave it out and connect pin 1 to pin 2 with a jumper.
3 2 1

OmniRat v1.0
Manufacturers and product names are mentioned solely for circuit identification, and where applicable their trademarks are the
property of their respective owners who are in no way associated or affiliated with the author. No cooperation or endorsement
is implied.
7
Rled can be somewhere between 1k5 and 10k (try 4k7). The lower the value the brighter the LED
shines, but at the cost of power consumption and wear of the LED.
The diagram is also based on star wiring where all ground connections go to the sleeve of the input
jack. It requires very good conductivity between the input jack, output jack and the enclosure to
work correct. If you do not have good conductivity, please connect a wire between the input jack
sleeve and the output jack sleeve.
Modifications
OpAmp
It all started with the LM308N Opamp. Through the years as these got obsolete it changed to the
OP07. Nowadays the LM308N can still be bought, but be aware of fakes!
Other alternatives are the CA3130 and TL070.
Actually you can use almost any single pin compatible OpAmp, but be aware that it is externally
compensated via pin 1 and 8.
Ring
Sleeve
Tip
Cathode (short leg)
Input
Anode (long leg)
Tip
Sleeve
Output
Rled

OmniRat v1.0
Manufacturers and product names are mentioned solely for circuit identification, and where applicable their trademarks are the
property of their respective owners who are in no way associated or affiliated with the author. No cooperation or endorsement
is implied.
8
Drill instructions
17,8mm
Volume Distortion
Tone/Filter
17,8mm 17,8mm
Holes for the potentiometers should be 7mm.
Troubleshooting
All PCB’s have been 100% factory e-tested and out of every batch I receive I build an effect to double
check, so there should not be a connection problem on the PCB itself.
The board is not working (at all), what now?
•Check if your 9V is plugged in correctly (and/or soldered correctly on the board). Pay special
attention to the polarity.
•Check that you oriented the capacitors, IC’s ,transistors and diodes the right way. SMF, MKT
and ceramic capacitors as well as resistors do not need to be oriented. A likely sign of
incorrect capacitors and/or orientation is when an effect is sputtering, rumbling or
“motorboating”.
•Check if you used the correct values of the components. For resistors you can look here:
http://www.diyaudioandvideo.com/Electronics/Color/
•Double and triple check your soldering! A loose or cold solder can be really bad for your
board.
•Replace the IC and/or transistors, one might be defective. Before doing that first unplug the
9V and wait for 5 seconds.
•Check that you have good/high grade components. A lot of Chinese sourced parts are fakes
(especially high end opamps, audio capacitors, vintage diodes and transistors) so be careful
that you source your parts from reliable suppliers.

OmniRat v1.0
Manufacturers and product names are mentioned solely for circuit identification, and where applicable their trademarks are the
property of their respective owners who are in no way associated or affiliated with the author. No cooperation or endorsement
is implied.
9
Schematic