OtalgiaFX MOSFET BOOST User manual

Build Guide
October 2019
MOSFET
BOOST
OtalgiaFX
www.otalgiafx.co.uk
“A nice clean Mosfet booster
based on a popular crackling
boutique pedal ”

** Please note that this some of the
parts in this list are interchangeable.
For example you can use carbon
resistors instead of metal film,
however it is possible that changing
these components might alter the
sound slightly.
PART LIST
BILL OF REQUIREMENTS
PART
VALUE
DEVICE TYPE
CAPACITORS
C1
100nf
5mm Polyester Box, 63v (or higher)
C2
10uF
Polarised Electrolytic, 25v (or higher)
DIODES
Z1
9v1
Zener
RESISTORS
R1
5K1
1/4W Through Hole, Metal Film
R2
10M
1/4W Through Hole, Metal Film
R3
10M
1/4W Through Hole, Metal Film
R4
100K
1/4W Through Hole, Metal Film
TRANSISTOR
T1
BS170
Mosfet, 500ma, 60v
POTENTIOMETER
GAIN
C5K
16mm Anti-Log Taper, Pin Terminals

BUILDERS NOTES
In the parts list each component has a component number. This number corresponds to the placement number silk
screen printed on the top of the PCB. Components should be mounted on the printed side of the PCB and
soldered into place on the underside of the board.
To aid in construction and make soldering easier it is suggested that components are soldered to the board in
order of their height profile from low to high, starting with resistors, diodes and then progressing on to larger items
such as sockets and capacitors. The potentiometer should be soldered last.
Some items may require correct orientation for the circuit to work correctly as documented below -
Polarised Capacitors -
The PCB will have a “+” mark printed. This mark indicates where the positive lead of the capacitor should be
soldered. In general the positive lead of a polarised capacitor is longer than the negative. Also in many polarised
capacitors the body of the component will be marked to indicate the polarity of each lead.
Transistors-
The transistors will need to be orientated correct and match the placement image marked on the PCB. If you intend
to use transistors that differ from the build list then please be aware than the Collector, Base and Emitter legs may
be in a different order. The pinout legs of different transistors can be found by referring to their technical data
sheets on the Web.
It is also worth noting that transistors are susceptible to heat damage so take care when soldering. Alternatively use
transistor sockets and insert the transistors after the sockets have been soldered into place.

BUILDERS NOTES (ctd)
Diodes -
A diode has 2 sides - a Cathode and Anode. The Cathode side of a diode has a circular band printed around
the body of the component to aid identification. The PCB is printed to also showing this this marking to aid
correct orientation. Zener Diodes are sensitive to heat & static so take care when handling / soldering, or
maybe consider use of sockets for mounting.
Resistors -
Resistors are not polarised so can be mounted either way around.
Non Polarised Capacitors-
Non-Polarised capacitors can be mounted either way around.
Potentiometers -
The potentiometers should be mounted onto the topside of the PCB with it splined shaft facing outwards.
Please refer to the picture later in this document if in doubt.

BUILDERS NOTES (ctd)
When mounting this circuit into an enclosure the potentiometer will hold the PCB in place within the enclosure
and stop the circuit board from moving around. Please take care when mounting the potentiometer not to
over tighten the nut or you might damage the potentiometers thread.

TESTING THE CIRCUIT
Before proceeding to the off board wiring of switches and LED’s it is advised to test that the circuit is working
as expected. To do this you need to solder four wires from the connectors on the PCB, marked I,O,9V & G.
The connectors are sized to accommodate AWG24 Single Strand Wire. If using this wire be careful not over
bend it as it may snap. If you are not comfortable with handling single core wire then stranded may also be
used.
To test your circuit -
1. Unplug the power supply
2. Plug a mono guitar cable into your guitar and a second mono guitar cable into your amplifier
3. Connect the wire from I (This is the input wire) to the tip of your guitar cable
4. Connect the wire from O (This is the output wire) to tip of your amp cable
5. Connect the wire from 9V (This is the Voltage wire) to the +9V of your power supply
6. Connect the wire from G (This is the Ground wire) to the sleeve of your guitar cable, the sleeve of the amp
cable and to the Ground wire of your power supply.
7. Plug in the power supply and test the circuit is working. If it is then you can proceed to off board wiring.
The easiest way to perform off board wiring is to use a 3PDT switch daughterboard -
https://www.otalgiafx.co.uk/wp-content/uploads/2017/09/3PDT-Instructions.pdf

Schematic