God City Instruments – Bass Brutalist V1.2 Build Guide
1
GOD CITY INSTRUMENTS – Bass Brutalist V1.2 Build guide
The God City Instruments (GCI) Bass Brutalist is an overdrive pedal derived from the Brutalist Jr. circuit but with
component values and circuit topology tailored specifically for bass instruments. The circuit consists of two op amp gain
stages and a tilt EQ inspired by the DOD FX10.
The first gain stage is non inverting and resembles a fixed-‐gain Rat in that there are two RC pairs shunted to ground in
the negative feedback path. Each of these RC pairs form high pass filters which also influence gain. Larger caps allow
more bass into the circuit. Larger resistors also allow more bass into the circuit, but reduce gain. A popular mod here is
to reduce the resistor value, creating a thinner, but tighter sound with more distortion. Try replacing these resistors
with pots. While the op amp in this stage is not crucial, it’s a dual op amp who’s other side is used for the EQ control.
For adequate EQ headroom, it’s advised to use hifi, rail-‐to-‐rail op amp. A TL072 will work in a pinch, but an OPA2134 will
likely sound better.
The second gain stage is inverting with asymmetrical soft clipping provided by a pair of mismatched LED’s. Try different
clipping diodes for different sounds. The op amp chosen is an OP07 for its association with the Pro Co Rat. It’s slow-‐ish
slew rate seems well suited for producing focused mids in a bass guitar. Try a TL071 if a more hifi sound is desired.
The EQ stage a highly balanced active tone stack which can provide a large bass or treble boost. Making changes here
can quickly knock the stack out of balance. To brighten the pedal, build using the stock FX10 values; R8 = 10k, R12 = 22k,
R13 = 3.3k, C6 = 120p, C9 = 0.1u, C14 = 10u. For a more extreme bass boost, build using these values; R8 = 68k, R12 =
100k, R13 = 1k, C6 = 4.7n, C9 22n, C14 = 47u. Thanks to John Snyder of Electrical Audio Experiments for help simulating
these frequency responses.
This pedal is an easy build, but this guide is intended for people who have some experience building pedals. Component
sourcing, component identification, assembly techniques, wiring stomp switches, etc. is not covered. The GCI Brutalist
Jr. assembly guide has helpful information for less experienced builders. That guide can be found here:
http://www.kurtballou.com/brutalistjr/
Available separately is the GCI 3PDT utility PCB for PCB pin 3PDT footswitches. This PCB makes footswitch wiring quick
and easy. Not compatible with solder lug style switches.
Don’t forget to connect the ground pad of the PCB to the ground lug of the input, output, and DC power jacks!
Due to the scope of this project, technical support is not available. However, consider joining the GCI DIY PCB Builders
group on Facebook to get advice from and share your work with other builders. We require that all group members
agree to the rules before being accepted into the group.
https://www.facebook.com/groups/2454786551255317/
Component values for the PCB as well as some alternate values are listed below. This is a BOM for the PCB only.
Resistors and diodes are 6.3mm leg spacing, film and ceramic capacitors are 5.08mm leg spacing, and electrolytic
capacitors are 2.54mm leg spacing. I/O jacks, DC jack, switch, enclosure, and knobs are not listed. The schematic and a
drill template for a 125B (1590N1) sized enclosure are also attached.
