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2 layers121.9 × 149.9 mmYellow fuzz dev, the printed circuit board in 3D

Yellow fuzz dev

ersatzavian/yellow_fuzz

A bass fuzz for my good friend! Don't tell him, it's a surprise. Starting with a Boss MT-2 (I know, ew, don't tell anybody) because that's allegedly how Arion Salazar got most of his fuzz tone's on Third Eye Blind's…

Full screenGitHub.kicad_pcb
Size
121.9 × 149.9 mm
Copper layers
2
Thickness
1.59 mm
Parts
165
Nets
111
Pads
426
Tracks, vias
989, 149
Pours
2
Routed
Yes
KiCad
KiCad 5 (file 20171130)
Created
1 Dec 2019
Updated
20 Sep 2021

Overview

Yellow fuzz dev is an open-source printed circuit board by ersatzavian, from the ersatzavian/yellow_fuzz repository on GitHub. It is a 2-layer board of 121.9 × 149.9 mm with 165 parts on 111 nets, routed with 989 tracks and 149 vias.

It is built around the TL072CP, BC817-25-TP and BAS16W, with the PTV111-4420A-A104, 1N34A and DMN2041L among its other parts. Its parts include 66 resistors, 50 capacitors, 14 transistors, 12 connectors and 11 diodes.

Main components

12

README

readme.md

Graduator

What?

A bass fuzz for my good friend! Don't tell him, it's a surprise. Starting with a Boss MT-2 (I know, ew, don't tell anybody) because that's allegedly how Arion Salazar got most of his fuzz tone's on Third Eye Blind's self-titled (check out 2:20-2:30 in Graduate, of 4:10 in Thanks a Lot if you like yours with phaser). Hell yeah we want that, don't pretend you don't like that record.

Formerly "yellow fuzz" after BRC's "yellow bikes" that happen to be green. Didn't like the sound of it, now it's the Graduator.

Rev 01

Rev01 (non form-factor) has been built, brought up, and play tested.

SN00

Rev01 User Guide

Electric Druid has an awesome write-up on the key circuit blocks in the original MT-2 design that's worth a read. If you want a comprehensive survey of the guts of this pedal, read that, then the mods section below, and you're done.

Controls

Controls are described by order in the signal chain, rather than physical layout.

Rev01 Controls Labeled

ControlOriginal MT-2 Control, or ExperimentCircuit BlockWhat's it Do?
GainExperimentDistortion Block - First Op-Amp Stage Gain, P1. GainThe "pre-distortion" gain block does two things:
  • Applies a band-pass-filtered boost (the center frequency of this boost has a mod described separately).
  • Demands enough gain from op amp U1A to cause some distortion when at high gain setttings.
In the original MT-2, the gain of this stage is fixed. In the graduator, the feedback resistance here can be reduced, which reduces the gain. If the pre-boost filter is ignored (or the pre-boost filter select switch is used to skip the pre-boost filter), this control doesn't really do much at all; the end result of reducing the gain here is audibly identical to reducing the "Distortion" control. But with a filter selected, this control lets you choose how much that initial band-pass boosts, which can be kind of interesting. Definitely won't be included in the form factor design, but merits playing around with while you're playing the the pre-boost filter select.
Pre-Boost Filter SelectExperimentDistortion Block - First Op-Amp Stage Gyrator Select, SW1. Pre-Boost Filter SelectAs you can read about here, "gyrators" are nifty little active circuit blocks that let you make a thing that acts like an inductor out of a capacitor and a transistor or op-amp. Why not just use an inductor is a good question and is covered in that guide in good detail. For our purposes here, this control lets you pick between two filters, or a third disable setting:
  • A stock filter which is described in the electric druid guide; it's a 36dB boost centered at 1 kHz with a "Q" of 2.8 ("Q", or "Quality Factor" describes how narrow and pointy that bandpass's frequency response is; a filter with high "Q" will be super pointy and really impact just its center frequency, while a filter with lower "Q" will be more gradual and wide and impact frequencies up and down the band around its center.).
  • A modified filter: 36 dB boost centered at 224 kHz, with a Q of 3.2. I made this mod to push the boost down into a range I thought might be better for a bass fuzz.
  • The disable setting just floats the switch terminal, which is kinda a bug because it takes the feedback (the "gain" control) out of the mix. You'll notice some volume variation going to and from this setting depending on where the "gain" is set. I may fix it. I may not.
A bonus feature of this section is that one or both of these filter blocks could be retuned by changing a few parts, letting you do A/B comparison between a setting you like and a new setting you're considering.
DistortionOriginalDistortion Block - Second Op-Amp Stage Gain, P2A/B. DistortionControls the gain of the second op-amp stage before the diode limiter that really clips the signal. Running this op-amp at high gain will boost the signal to the "rails", and you'll get very hard, square peaks, before you even hit the diode limiter. There are many different sources of distortion in this pedal, it's definitely not all up to just one circuit block to hammer your signal into a mess.
Diode Select SwitchesExperimentDistortion Block - Diode Limiting Stage, SW2 / SW3 Diode SelectThe core of this pedal, as with many distortion pedals, is the diode limiter. This stage takes your nice sine-shaped waveform and clips the peaks off of it when they exceed the forward voltage of the diodes. Different diodes have different forward voltages, and different response "shapes" as they effectively turn on and off. The internet is full of forums where people will swear that this diode does this or that and sounds this way or that way, and many of them are subjectively right but nearly all of them are oversimplifying the test case they're talking about. Since there are so many sources of distortion in this (and every) circuit, you're hearing them all. The diode is just part of it. Anyway, this mod lets you pick between three different kinds of diode for your limiter. Even weirder, it lets you choose the diode for the top and bottom half of your waveform separately, so you can produce very "asymmetric" distortion. Right now, you have:
  • A Silicon diode, the generic 1N4148, with a forward voltage around 1V.
  • A Germanium diode, the generic 1N34A, with a forward voltage around 1V.
  • An LED, Kingbright WP7113QBC/D. This is a blue LED, and has a forward voltage of not less than 2.4V. This is really a bug; I should have used a red or yellow LED with a forward voltage closer to the other two, so that you could compare tone without comparing volume - you'll notice right away that the blue LED is louder than the other diodes. I like how it sounds, though, so I'm considering that a future experiment and letting it ride.
Just like the pre-distortion boost section, this section is a great place to swap out components you're curious about and A/B test stuff.
Diode Series Resistance ControlExperimentDistortion Block - Diode Limiting Stage, P3 / P4. Diode Resistance ControlDiode clipping can be very harsh and introduce harmonics that you wouldn't get from, say, output stage distortion in a tube amplifier, which can sound really buzzy and cheap and not great. In an attempt to prevent this, I added 1k potentiometers - variable resistors - in series with the diodes, to soften the "knee" when they turn on and off and try and reduce that fuzz. In practice, the EQ section of this pedal has way, way more impact on the harmonic content that makes it out of the pedal, and I find this control completely inaudible.
Post-Boost Filter EnablesExperimentDistortion Block - after Diode Limiting Stage, SW4 / SW5. Post Boost Filter ControlThe original MT-2 includes this stage with both Gyrator sections included, which provides a "double-humped" bandpass boost. In the original, the two sections are:
  • A ~5dB boost at 105 Hz with Q=14.6.
  • A ~10dB boost at 4.9 kHz with Q=2.2.
In the graduator, the two sections are:
  • A ~5dB boost at 333 Hz with Q=4.6.
  • The original ~10dB boost at 4.9 kHz with Q=2.2.
There are really two mods here:
  • I've moved the lower peak up the frequency spectrum and fattened it up a bit.
  • Both peaks can be enabled or disabled with the respective switches.
This is a little more subtle to play with than I expected, and I like that. Try it out.
EQ - LowOriginalTone BlockThe original "low shelf" control, a band-pass filter centered at 105 Hz with a Q of 3.1, which can provide up to 20dB of cut or boost. The whole EQ section is covered very nicely with plots in the Electric Druid guide, highly recommend.
EQ - Mid FrequencyOriginalTone BlockThe original "mid frequency" control, which controls the center of the mid band-pass filter. Filter center frequency can be swept from about 200 Hz to about 7 kHz. This control would be a lot better as a log taper pot, to spread the frequencies of interest logarithmically along the range of the pot, but a dual-ganged log-taper 50kΩ pot is not an easy thing to find. As a result, you'll hear this control really come to life between about 1 o-clock and 5 o-clock.
EQ - MidOriginalTone BlockCut or boost up to 15 dB with the mid-band filter centered wherever you put it with the Mid Frequency knob.
EQ - HighOriginalTone BlockHigh Shelf EQ, begins to kick in around 1kHz, where it offers around 6 dB of cut or boost, and flattens around 10 kHz, where it offers around 20 kHz of cut or boost.
LevelOriginalTone BlockYou know what this does.
Enable / BypassOriginalSwitching SectionYou know what this does too.

Mods

ChangeGoalDone
Make gyrators after clipping stage optional (see C24/C25, C20/C17)Experiment with pedal character to reduce fizz and deliver more even tone to the eq section so I can hear the difference.Yes
Add bypass option for preboost stage.Try to reduce fizz.Yes
Add series variable resistors (trim pots) to clipping diodes D3/D4.Try to reduce fizz.Yes
Add selector switch for 3 different diode options in each direction.Experiment with higher Vf (LEDs) and give germanium a whirl.Yes

Issues

Rev01 (Non-Form-Factor)

IssueWorkaroundFixFixed in Master
C2 and R6 ref designators are swapped. HTML BOM shows correct outlines.Install per HTML BOM.Swap ref des back.
R4, R6-7, R12, R14-15, R17-18, R24-26, R33, R51 MPN is for 1k part, should be 10k (part description on BOM is correct, but MPN is wrong).Install 10k part.Update component in lib.
R14 and R15 ref des are colliding.N/AFix in layout.
NSVJ3910SB3T1G was replaced in order with J113, which is a through-hole part and won't fit.Order correct part.Make sure MPN in design is correct and orderable.
PTV111-4420-A104 was missing from kit, got extra PTV112-4420-A104 instead.Cut leads 1 and 2, bend 3-6 down to fit into pads 1-4 to use just one pot of the two in the package.Order the right thing.
PTV111-4420-A503 was missing from kit, got extra PTV112-4420-A503 instead.Cut leads 1 and 2, bend 3-6 down to fit into pads 1-4 to use just one pot of the two in the package.Order the right thing.
Nichicon UST1H010MDD1TE footprint is wrong (C1, C19, C26, C36, C43, C46): lead spacing is nto correct, part leads are flared for wider spacing than footprint.Bend leads back.Correct footprint.
D6 missing MPN info.N/ACorrect part library ref.
No test points, doh.N/AAdd some ground test points and stage-to-stage test points and jumpers.
22 Ohm series-R on power rail, why even would you do that?Short that.Remove that.
Polarity marks on op-amps are not visible enough, and are obscured when sockets are installed (U1 was installed rotated 180 degrees in first build).Note polarity carefully during build.Improve op amp polarity marks.
Pre-distortion boost gain pot P1 is backwards (CCW for more)Turn it the other way, or snip top-side trace between pins 1-2, short pins 1-3. Sch LayoutCorrect in schematic.
Dual pots installed in P5, P6, P7, and P9 with pins 3-6 slid over into pads 1-4 don't match design correctly.Double-check pinout of these parts and revise rework used to place dual pots in single-pot footprints.Use the parts on the BOM, duh.
Duplicate TONE_OUT net names caused short across level pot. Tone Out IssueCut extra trace on top layer. Tone Out WorkaroundRemove duplicate net label.
Incorrectly routed jack as center-positive, which makes the battery not work at all.Cut and swap traces to make center-negative. Jack ReworkPermanentify rework.
Mid frequency control only does much between about 1-o-clock and 5-o-clock.Use as is.Try once more to find a log pot... good luck.
Pre-boost filter select switch SW1 should probably have a resistor on its unused pole, rather than having fixed gain and taking the "gain" control out of the mix.

Parts Needed

For Rev02 (Form-Factor)

  • 1/4" Stereo Jack, Panel Mount with header footprint.
  • 1/4" Mono Jack, Panel Mount with header footprint
  • Re-evaluate all potentiometer tapers and footprints.

Play testing notes

  • It sounds... like an MT-2 with some stuff changed.
  • The pre-filter change is the most interesting, as swapping diode types.
  • Post-filters are also interesting, but a bit less so.
  • Still many settings that produce lots of unpleasant fizz. Tonally I'd still say it's "mostly bad with the ability to do some good things."
  • Series-R on the dioes does exactly nothing. On the scope, it does visibly soften the knees a little, but by the time this has been through the tone section, that does the same thing.
  • Secondary control on the initial boost gain does exactly the same thing as the drive control. Might try playing with it a bit more with the pre-filter set to off, but for the most part just set it to 10 and leave it.

References

Other Pedals I'm eyeing

  • DOD FX91 Bass Overdrive
  • Darkglass - Duality
  • Zvex - Wooly Mammoth
  • Death by Audio - Fuzz War
  • Bass Big Muff
  • MXR Bass Fuzz
  • Fairfield Barbershop

Parts

165
QtyValueFootprintReferences
1410kResistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR1, R3, R4, R12, R14, R15, R17, R18, R24, R25, R26, R33, R35, R51
9100kResistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR2, R13, R19, R32, R42, R46, R48, R53, R57
91MResistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR6, R7, R40, R43, R44, R50, R52, R55, R62
8BC817-25-TPdigikey:SOT-23-3Q5, Q6, Q7, Q8, Q9, Q10, Q12, Q13
72.2kResistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR8, R10, R23, R56, R58, R65, R66
747nCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC2, C5, C13, C23, C32, C35, C39
60.1uCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC4, C10, C25, C40, C45, C48
61uCapacitor_THT:CP_Radial_D4.0mm_P1.50mmC1, C19, C26, C36, C43, C46
510uCapacitor_THT:CP_Radial_D5.0mm_P2.00mmC15, C17, C34, C37, C50
51kResistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR16, R20, R21, R28, R54
547kResistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR9, R11, R29, R61, R63
422kResistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR36, R38, R45, R59
456kResistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR37, R39, R47, R49
4NSVJ3910SB3T1GOSCT-NDPackage_TO_SOT_SMD:SOT-23_HandsolderingQ2, Q4, Q11, Q14
4TL072CPyellow_fuzz_dev:DIP-8_W7.62mmU1, U2, U3, U4
3100uCapacitor_THT:CP_Radial_D5.0mm_P2.00mmC8, C11, C12
310nCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC7, C30, C41
3BAS16WPackage_TO_SOT_SMD:SOT-323_SC-70D1, D10, D11
3PTV111-4420A-A104yellow_fuzz_dev:Potentiometer_Bourns_PTV111_4420A_Single_VerticalP5, P6, P7
3SW_SP3T_A24JPyellow_fuzz_dev:A24JPSW1, SW2, SW3
3WP7113QBC_Ddigikey:LED_5mm_RadialD3, D6, D9
2100pCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC9, C44
210pCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC27, C42
215nCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC18, C20
21N34Adigikey:DO-35D5, D8
21N4148digikey:Diode_DO-35_P10mmD4, D7
2220nCapacitor_THT:CP_Radial_D5.0mm_P2.00mmC22, C38
2220pCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC29, C31
2330Resistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR60, R64
23362P-1-102TLFyellow_fuzz_dev:3362PTP3, P4
2470pCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC28, C33
247pCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC16, C24
2DMN2041LPackage_TO_SOT_SMD:SOT-23Q1, Q3
2SW_SPST_A11JPyellow_fuzz_dev:A11JPSW4, SW5
11.0uCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC3
11.2kResistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR22
11.5nCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC21
1100Resistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR41
11825910-6yellow_fuzz_dev:Switch_Tactile_THT_6x6mmS1
122Resistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR5
122nCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC49
127nCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC6
13.3kResistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR34
13386P-1-204TLFyellow_fuzz_dev:3386PP1
133nCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC14
14.7kResistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR27
1470Resistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR30
1470kResistor_SMD:R_0603_1608Metric_Pad1.05x0.95mm_HandSolderR31
18.2nCapacitor_SMD:C_0603_1608Metric_Pad1.05x0.95mm_HandSolderC47
1BC9VPCyellow_fuzz_dev:Battery_Holder_9V_BC9VPC-NDBAT1
1DZ2S056X0LDiode_SMD:D_SOD-523D2
1LOGOyellow_fuzz_dev:amph_1_5x1_5G***
1PJ-202Ayellow_fuzz_dev:Barrel_Jack_5.5mmODx2.1mmID_PJ-202AJ1
1PTV111-4420A-A503yellow_fuzz_dev:Potentiometer_Bourns_PTV111_4420A_Single_VerticalP9
1PTV112-4420A-A104yellow_fuzz_dev:Potentiometer_Bourns_PTV112_3417A_Dual_VerticalP2
1PTV112-4420A-A503yellow_fuzz_dev:Potentiometer_Bourns_PTV112_3417A_Dual_VerticalP8
1RA49B11yellow_fuzz_dev:Headphone_Jack_6.35mm_SN49B12BJ2
1SN49B12Byellow_fuzz_dev:Headphone_Jack_6.35mm_SN49B12BJ3

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Questions

How big is the Yellow fuzz dev PCB?

It measures 121.9 × 149.9 mm and has 2 copper layers, 1.59 mm thick.

What parts does the Yellow fuzz dev use?

165 parts, built around the TL072CP, BC817-25-TP, BAS16W and PTV111-4420A-A104. 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 Yellow fuzz dev KiCad files?

From the ersatzavian/yellow_fuzz repository on GitHub, at the commit this page was made from: the board is yellow_fuzz_dev/yellow_fuzz_dev.kicad_pcb. PCBKit opens the board in the browser, with nothing to install.

Can I use the Yellow fuzz dev design in my own project?

Its repository states no licence, so its author keeps all rights: ask ersatzavian before reusing the design.