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goya1746

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Overview

goya1746 is an overdrive & preamp pedal based on the legendary Diezel VH4 channel 3. Fully open circuit board designed in KiCad 8. The main idea was to avoid oscillations on all gain levels. This project is shared for hobbyists who want to study, modify, or build their own. The full PCB outline is 115 × 70 mm (4.53 × 2.76 in), but the usable area is about 96 × 70 mm (3.78 × 2.76 in) if you remove the side "wings" in KiCad and define your own edge cut before generating Gerbers. In theory, it should fit a 1590BB enclosure, but keep in mind that each potentiometer is wired separately and the connection pads are not located at the corners of the PCB, so there will be quite a lot of wiring inside.

Manufacturing

Check Releases page for .zip Gerber files ready for production. If you want to fabricate the PCB, just upload the .zip Gerber files to your favorite board house (e.g. JLCPCB, PCBWay, NEXTPCB). Make sure you can source all components in the correct form factor before manufacturing the board.

Important notes

This pedal should be powered with 12-18VDC. Power draw 100mA. There are claims that 15VDC provides the best results because it generates less heat in the voltage regulator, but 18VDC is the standard.
The LM2940 regulator is installed vertically. Its metal tab can be mounted to the chassis to help dissipate heat — just make sure the chassis is grounded and not connected to any other signal paths. This workaround increases build complexity and will be refined in a future revision. The goal was to minimize board temperature to prolong the lifespan of nearby electrolytic capacitors.
Only five electrolytic capacitors are used, and they are strategically placed to provide shielding for the TC1044SCPA charge pump switching regulator IC from nearby components.
Some capacitors, specifically C3, C4, C5, C9, C12, C17, C18, C20 and C22, that were originally electrolytic, have been replaced with film capacitors. The schematic remains unchanged, but the PCB footprints are different. You can still install electrolytic capacitors in those positions, but be sure to observe the correct polarity. Future revisions will return to electrolytic capacitors because they're cheaper and the experiment didn't produce a better tone.
The resistor 2.2K 1/4W for the LED 12V should be placed on the wire that connects it to the PCB. Adjust the resistor value to achieve the desired brightness.
Even though the LM2940CT-12/NOPB voltage regulator provides reverse-polarity protection for the entire circuit, it is still good practice to solder a 1N5817 Schottky diode in series with the + wire leading to the DC input. The striped end (cathode) should face the PCB. For example: DC Jack → [Anode — Diode — Cathode] → PCB. You can see this approach used in almost all PedalPCB schematics. Make sure you identify the +V and Ground pins of the DC input by referring to the PCB design in KiCad.
For experimental purposes, the mid-pot tone control is wired in the so-called "Marshall style," which gives the mid control a stronger effect and shifts the tone toward a punchier, more mid-rich sound compared to a "Fender style" tone stack. To switch back to the "Fender style" configuration, connect pins 2 and 3 of the MID potentiometer together.
Because of space limitations in this version, buffered bypass solder pads are not included. This may be added in a future revision. At the moment, the on/off switch must be wired as a true bypass by the builder. Or, if you're feeling hacky, you can connect a wire between the C3 capacitor and the R4 resistor (for example, to the side of the R4 resistor that isn't connected to Ground), and that will be your buffer. And the signal after R17 should be shorted to Ground during bypass.

P.S. Future releases are not expected in the near term due to financial constraints. However, once the situation improves, development will continue, including projects such as Turbo Rat, SansAmp GT-2, Boss CE-2, as well as a search for the best fuzz circuit.

Acknowledgments

Diezel for inspiring design of modern high-gain amplifiers.
freestompboxes.org and its community — without their prior work, this project would not have been possible.
pedalpcb.com DIY shop, for inspiration and clear, easy-to-understand schematics.
aionfx.com for showing how things can be changed.
pcbguitarmania.com for yet another reference and food for thoughts.
effectslayouts.blogspot.com for better understanding how the footswitch wiring should work.
techexplorations.com for great KiCad educational materials.
Hans Rosenberg for interesting talks about good PCB design in general.

Guides

These guides might help beginners who have never built their own pedals. Some links might become broken.

Bill of Materials

All resistors are 1/4 W metal film with 1% tolerance. All capacitors must have a minimum voltage rating of 35 V. Consider capacitors to be polypropylene film unless otherwise specified. If 25 kΩ potentiometers are unavailable, a 50 kΩ potentiometer may be used together with a 50 kΩ resistor in parallel. This changes the taper slightly (especially for log pots), because the resistance curve is altered by the parallel resistor. Ferrite bead R1 is optional and can be replaced with a wire link. The OPA2134 at U1 may be substituted with another TL072 without any noticeable difference.

You'll also need:

6.3 mm jack sockets,
DIP8 sockets for each op-amp and a charge pump,
optional JST connectors for DC input and LED,
a plastic DC input jack wired for center negative.

This pedal provides two output options: Guitar Out and Power Out. In most cases, you won't need to wire both. If the pedal is used at the end of a signal chain (similar to a real amplifier), Power Out is the preferred choice. Power Out is a low-impedance, line-level signal, so it can be safely connected to standard line inputs, such as those on audio interface. Guitar Out is a traditional high-impedance output suitable for connecting to other pedals or amp inputs.

For ICs and other essential components, use reputable suppliers only. Avoid sources like eBay or AliExpress, as counterfeit or unreliable parts are widespread on those platforms and may cause malfunction or failure.

Reference	Value	Qty	Notes
BASS1	A1M	1
C1,C7,C15,C16	22n	4
C2,C6,C13	100p	3	Ceramic Disc
C3,C4,C5,C17	1u	4
C8	2n2	1
C23	2n2	1	Ceramic Disc or Film
C9,C12,C18	2u2	3
C10	47p	1	Ceramic Disc
C11	4n7	1
C14	560p	1	Ceramic Disc
C19	330n	1
C20,C22	10u	2
C21	1n	1	Ceramic Disc or Film
C24,C25,C26,C27,C28	47u	5	Electrolytic ~35V
D1,D2,D5,D6	1N4148	4	Signal diode, DO-35
D3,D4	1N4734A	2	5.6V zener (equivalents: 1N752, 1N5232), DO-41
D7	LED 12V	1	Require ~2.2K resistor
J1	GUITAR INPUT	1
J2	DC INPUT	1
J3	POWER OUT	1
J4	GUITAR OUT	1
R1	FerriteBead	1	Optional
R2,R3,R14	1M	3
R4,R5,R15,R25,R37	100K	5
R6,R13,R18,R33	10K	4
R7,R10,R11,R17,R19	220K	5
R8,R16	470K	2

Ground & Shielding

The chassis should be properly grounded to ensure effective shielding and noise reduction. Where possible, use cables with an outer braided shield and connect the shield to ground at least on one end — preferably at the PCB side. The metal backs of potentiometers may also be connected to ground to help reduce noise pickup through their housings. Ground loops are generally not a concern inside a small enclosure such as a pedal, so a strict star-ground topology is unnecessary. The DC input jack must be plastic (isolated from the enclosure). Most pedals use a negative center power supply, so a metal jack touching the chassis could short the positive voltage to ground.

As a side note. There are a lot of myths and misconceptions about grounding in PCB design, mostly because of the many variables that need to be considered together with each statement. At some point, you think you understand how it works, but then you realize you don't. It's not always clear what the real cause of a problem is, and fixing one issue can accidentally fix another, leading to false conclusions.

For example, advanced grounding techniques are mainly used for high-frequency applications, and the effects are often negligible in the audio range (up to 20 kHz). Through-hole components are considered obsolete for high-frequency PCBs, yet they are abundant in most analog music equipment. If we start replacing everything with SMD components, we might lose some of the unique characteristics that contribute to the sound we expect, or just our own perception might change.

And let's not forget that the sound we're looking for doesn't always have to be perfect — it just has to be pleasant to our ears. Who wants to listen to a perfectly clean sine wave, right? We enjoy it when it's mixed with other harmonics and subtle modulations that make the sound feel alive. Often, it's exactly those imperfections in the components and PCB layout that create the desired effect.

PCB Specifications

Layers: 2
Thickness: 1.6 mm
PCB Size: 115 x 70 mm (4.53 × 2.76 in)
Copper weight: 1 oz (default PCB fab)
Trace clearance: 6 mil or 0.1524mm
Soldermask: [Black / Green / Anything]
Silkscreen: [White]
Surface finish: HASL
Material: FR-4
Via finish: Tented
Min. Drill Hole: 0.3 mm
Assembly: Through-hole components only (no SMD)

Recommended Fabricators

NEXTPCB
JLCPCB
PCBWay

Gallery

3D View Front Clean 3D View Back

PCB

TODO

Add a connection pad for the buffered output between C3 and R4, and find a suitable location for it on the PCB. Add a connection pad after R17 to be able to short it to Ground during bypass. Update schematic.
Make configuration where all caps are the same type as in Diezel VH4 pedal since any difference could affect the tone.
Add + signs on a silkscreen layer for all connection pads to lower the risk of mistakes.
Position the voltage regulator so that it can be laid flat on the PCB. Add a ground plane underneath it for better heat distribution.
Consider adapting the PCB layout to fit more popular enclosures, such as 1590BB.
Would it be possible to rewire everything so that pots connected directly to the PCB? Estimate PCB size, production costs and a headache of acquiring the correct pots.

License

Contribution

If you build this pedal, feel free to share photos or mods via Discussions. If you are an experienced Electronics Engineer or PCB Designer and see how something could be improved for the benefit of all, please submit an issue.

PCB design of a guitar pedal based on the 3rd channel of Diezel VH4 amplifier

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