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.

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.

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.

Components

Part

Value

Type

Part

Value

Type

22n

MKT

1% metal film

4u7

Electrolytic 25V+

560R

1% metal film

2u2

Electrolytic 25V+

1% metal film

MKT

1% metal film

100p

MLCC/Silver Mica

47R

1% metal film

MLCC/Silver Mica

1% metal film

4u7

Electrolytic 25V+

1% metal film

MKT

1% metal film

22n

MKT

1% metal film

C10

Electrolytic

25V+/MKT

R10

10k

1% metal film

C11

Electrolytic 25V+

R11

1% metal film

C12

100u

Electrolytic 25V+

R12

1% metal film

C13

10n

MKT

R13

100k

1% metal film

R14

100k

1% metal film

Distortion

A100k

Filter/Tone

A100k

Volume

1N4001

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

Turbo

RAT

Vintage RAT

You Dirty

RAT

33p

30p

3n3

2n7

3n3

C10

10u

10u (?)

D1-D2

1N914

1N4148

LED

1N4148

1N34A

IC1

LM308N

LM308 / OP07

OP07

LM308N / OP07

OP07

2M2

1k5

1k6

2M2

R11

10k

R12

47R

47R or 100R

47R

A150k

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.

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.

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.

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.

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.

Schematic

Table of contents

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