Frequency Central Meth Amp Rev.2 Manual

Frequency central
Build documentation for:
Meth amp Rev.2
Meth Amp is based around the fuzz core of the EH Big Muff pedal. The clipping diodes have
been replaced by red LEDs to take account of the change in power supply from 9V in the
original Big Muff to +/-12V in Meth Amp. To the fuzz core has been added a bunch of OTAs,
each controlling a different aspect of audio processing: gain, regen (a new feature –not
present in Big Muff), tone and volume. Thereby, each feature is fully voltage controllable.
Additionally, there is a separate x100 preamp which can be used to boost external audio for
further processing by Meth Amp.
Main PCB: Panel PCB:
Please observe correct polarity of the electrolytic caps (indicated by +), transistors, ICs (pin 1
indicated by square pad), LEDs (cathode indicated by flat edge) etc!
‘n’ = npn transistor BC547
‘p’ = pnp transistor BC557

Bill of Materials
100R x 8
1K x 4
2K2 x 4
4K7 x 4
10K x 7
22K x 7
27K x 2
47K x 8
100K x 7
200K x 2
220K x 1
470K x 2
1M x 4
33pF x 1
150pF x 1
330pF x 1
470pF x 2
10nF x 2
100nF x 6
1uF electrolytic x 1
10uF electrolytic x 3
47uF electrolytic x 2
LM13700 x 2
TL072 x 2
TL084 x 1
BC547 x 2
BC557 x 4
3mm red LED x 4
B100K x 8
All pots are 9mm Alpha
100K trimmer x 4
All trimmers are 6mm
(Tayda)
Power header
Male header strip
Female header strip
Kobiconn sockets x 8

Main PCB:
Populate the Main PCB as shown on the silkscreen, starting with the lowest profile
components, so:
Resistors
IC sockets
Non-electrolytic capacitors, transistors, trimmers
Power header
Electrolytic capacitors
Finally, cut 3 male header strips to the correct lengths (4, 4, 4) and solder to the PCB so that
the long legs stick out of the rear of the PCB.
Panel PCB:
Populate the Panel PCB as shown on the silkscreen in this order:
Resistors
IC socket
Transistor
Potentiometers (bend back the mounting lugs , then solder the middle lug in place.
Reflow and adjust as necessary so that they all lie correctly. Solder lugs 1, 3 and the
mounting lugs)
Cut 3 female header strips to the correct lengths (4, 4, 4) and solder to the PCB so that the
black parts stick out of the rear of the PCB.
Now, place the 8 sockets onto the PCB with their ground lugs pointing towards the bottom
of the PCB. Don’t solder them in place yet! Assemble the panel to the panel PCB, put on the
pots washers and tighten up the nuts. Now set the sockets to the panel using the nuts,
making sure they all sit right. Place the assembly face down and solder the sockets in place.
This process should allow a small space to be created between the rear of the sockets’
bodies and the PCB, allowing jacks to go in balls-deep (!). Everything should line up nicely
now!
Take the whole thing apart, ie remove the nuts/washers and take the panel away from the
panel PCB. Now solder solid core (cut off resistor legs) between the sockets’ ground tabs
and the adjacent ground pads on the PCB. There is one ground pad per two sockets.
Plug the Main PCB into the Panel PCB…you’re done!
Tracking/calibration procedure
This is pretty straightforward, turn up all the CV inputs as well as the volume control, send
an envelope into each respective CV input and adjust the associated trimmer until DC
‘thunk’ is minimised.
http://www.frequencycentral.co.uk/ RDH 03/01/15