2 layers271.8 × 114.3 mm
Ardumower mega shield svn
Ardumower/ardumower
Develop an open source robotic lawn mower (HW+SW reference platform)
426 parts282
2 layers9.5 × 14.7 mm
Util BleedAFuzz
z2amiller/util-BleedAFuzz1A plug-in NPN transistor that biases like a lower-hFE part. In a single-transistor fuzz with collector-feedback bias (a large resistor from collector to base), the transistor's hFE mostly decides the DC collector…
- Size
- 9.5 × 14.7 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 5
- Nets
- 4
- Pads
- 13
- Tracks, vias
- 17, 0
- Pours
- 3
- Routed
- Yes
- KiCad
- KiCad 10.0 (file 20260206)
- Created
- 10 Sep 2026
- Updated
- 10 Sep 2026
Overview
Util BleedAFuzz is an open-source printed circuit board by z2amiller, from the z2amiller/util-BleedAFuzz repository on GitHub, published under the CERN-OHL-P-2.0 licence. It is a 2-layer board of 9.5 × 14.7 mm with 5 parts on 4 nets, routed with 17 tracks and 0 vias.
It is built around the BC847. Its parts include 2 resistors, 1 transistor and 1 connector.
Main components
1README
README.mdutil-BleedAFuzz
A plug-in NPN transistor that biases like a lower-hFE part. In a single-transistor fuzz with collector-feedback bias (a large resistor from collector to base), the transistor's hFE mostly decides the DC collector voltage, not the gain. So when everyone says a circuit "sounds best with a 125 hFE transistor" and all you have is 300s and 600s, what you actually need is the collector voltage a 125 would give. This board gets you there with a trimmer.
How it works
Q1 is wired straight across the header. A fixed 1M plus a 1M trimmer from base to emitter bleeds a settable share of the base drive, so the feedback resistor has to supply more current and the collector rises exactly as it would with a lower-hFE part. The bleed spans 1M to 2M. Effective hFE at a 50 µA stage:
| Bleed | BC847C (~600) | 2SC1815-GR (~300) |
|---|---|---|
| 1M | ~80 | ~70 |
| 2M | ~140 | ~110 |
LEAK is an optional 2.2M collector-base resistor that mimics germanium collector leakage (leave it off unless wanted).
Header order is E, B, C; plug a BC-series (C, B, E) socket in reversed.
Example: PedalPCB Overcast Fuzz
PedalPCB's Overcast Fuzz (build doc) is a Spirit in the Sky style fuzz: one gain transistor with 6M collector-to-base bias, a 470R emitter resistor and a 100K collector load, and the forum consensus is that it sounds best around hFE 125. With a 2SC1815-GR (hFE ~300) the collector sits near 2.0 V; a 125 hFE part would put it near 3.3 V with the gain control at minimum. Plug this board into the Q1 socket, put a meter on the collector, and trim until it reads about 3.3 V to nail the 125 hFE sound.
For circuits where the transistor's input impedance matters too (a Fuzz Face Q1 fed straight from the pickup), the companion util-DialAFuzz is the better tool.
Gerbers
GERBER-util-BleedAFuzz.zip is the JLCPCB-ready gerber and drill set; no KiCad install needed to order the board. One SOT-23 transistor, two 0805 resistors (one optional), a 3-pin header and a through-hole 1M trimmer on the back.
License
Licensed under the CERN Open Hardware Licence Version 2 – Permissive (CERN-OHL-P v2). See LICENSE and NOTICE.
You may make, modify, and sell boards from these files, with no obligation to publish your changes.
Parts
5| Qty | Value | Footprint | References |
|---|---|---|---|
| 1 | 1M | _MB_potentiometers:Variable Trimmer | RV1 |
| 1 | 1M | Resistor_SMD:R_0805_2012Metric_Pad1.20x1.40mm_HandSolder | R2 |
| 1 | 2.2M | Resistor_SMD:R_0805_2012Metric_Pad1.20x1.40mm_HandSolder | R1 |
| 1 | BC847 | Package_TO_SOT_SMD:SOT-23_Handsoldering | Q1 |
| 1 | Conn_01x03_Pin | Connector_PinHeader_2.54mm:PinHeader_1x03_P2.54mm_Vertical | J1 |
Questions
How big is the Util BleedAFuzz PCB?
It measures 9.5 × 14.7 mm and has 2 copper layers, 1.6 mm thick.
What parts does the Util BleedAFuzz use?
5 parts, built around the BC847. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the Util BleedAFuzz KiCad files?
From the z2amiller/util-BleedAFuzz repository on GitHub, at the commit this page was made from: the board is util-BleedAFuzz.kicad_pcb and its schematic util-BleedAFuzz.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the Util BleedAFuzz design in my own project?
Its repository publishes it under the CERN-OHL-P-2.0 licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).
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