After the introduction, analysis and breadboarding of two op-amp based guitar boosters, I’ll complete the pedal.
I’ll do the final schematic and bill of material, then do the soldering layout for a protoboard. I’ll plan out the enclosure, do some artwork and finalize the enclosure. I’ll finally assemble it and do test and demo.
Final Schematic
The base schematic did not change, it is exactly the same I used for breadboarding:
To complete the pedal I need the rest of the paraphernalia:
The only difference from my previous builds is that I wired footswitch slightly differently (I simplified it a bit), but other than that everything else is the same.
If you followed closely, you might’ve noticed that TL072 has two op-amps, and I only used one. Proper way to wire-up the unused op-amp is (see The Signal e-book):
This minimizes current consumption and cross-talk and improves performance. Since this is not really a critical application of an op amp, I would guess the effect of leaving it unconnected would be most likely minimal 🙂. Just being pedantic, that’s all.
The real shame is leaving it unused. Alternative would be to use TL061 or TL071 for example, they carry a single op-amp, but price difference is minimal and pinout is different from TL072. I also have loads of TL072s, and in more complex designs the extra op amp will come in handy.
Bill of Material
Here’s the final list of components:
| Designators | Component | Notes |
| 27969PSLA (1590A Hammond) | Enclosure | |
| Protoboard | SBB170 solder-in breadboard by Proto Advantage (fits into the enclosure … nearly) | |
| Jumpers and wires | 24 AWG solid core wire and 28 AWG stranded wire | |
| J3 | Cliff FC681473 | DC Power Socket |
| J1 | Switchcraft 112BX (or ACJS-MVS-3S Amphenol) | In – stereo Jack (alternatively use mono jack since I don’t use ring connector) |
| J2 | Switchcraft 111X (ACJM-MVS-2 Amphenol) | Out mono Jack |
| RV1 | 10K Linear Pot | ALPHA RV16AF-41-15R1-B10K-3 |
| Knob | Knob that fits 6.35mm straight shaft | |
| S1 | SF17020F-0302-21R-L | Taiwan Alpha 3PDT latching foot switch |
| C1 | 100pF | Ceramic cap (NP0/C0G) |
| C2 | 100nF | Metal film PET cap |
| C3 | 1uF | Electrolytic cap 25V |
| C4 | 22uF | Electrolytic cap 25V |
| C5 | 150pF | Ceramic cap (NP0/C0G) |
| C6 | 47uF | Electrolytic cap 25V |
| C7 | 100nF | Ceramic cap (X7R) |
| C8 | 100uF | Electrolytic cap 25V |
| R1, R6 | 100 ohms | 1% 250mW metal film |
| R2, R3 | 2.2M | |
| R4, R5 | 680 ohms | |
| R7, R8, R9 | 10K | |
| R10 | 1K | LED current limiting resistor |
| D1 | Led | 3mm Orange-Red, 2V forward voltage |
| U1 | TL072IP | TL072 in 8 pin DIP package |
| DIP-8 Socket | Socket so I don’t solder the chip directly |
I decided to use a socket for my chip so I don’t solder it directly to the board. Once the socket is in place I can simply pop in the chip.
The potentiometer I have is supposed to be mounted on a PCB. Solder lugs would’ve been preferable for this build since I’m not going to mount it on the PCB (RV16AF-10 model instead of RV16AF-41). But I got to work with what I have. Note – the model I have has shaft width 6.35mm, so some 6mm knobs might not fit.
Here are all of the components before I started assembling them:
Board Layout Plan
It gets a bit crowded with this many components, I found a nearly perfectly fitting proto-board (or solder-in breadboard, eh):
I very lightly sanded it (about 1mm or so but I did not need to cut it).
Here’s one way to lay the effect out on it:
Here’s DIY layout file as well:
Lots of wires (I hate wires) but unfortunately, with small board, sometimes this is inevitable.
Enclosure Planning
Here’s an excerpt from the SVG I used for planning:
In order to properly print it, I used SVG format since I could draw everything in actual millimeters for example. Using Inkscape I could plan this and print it exactly as per measures on the drawing. Here’s the SVG:
I prepared pdf version as well, it has to be printed without scaling (so scaling 100%, I was printing it on A4 paper)
Enclosure Artwork
I’m going to do decal for artwork, directly onto the “natural” finish. Same thing as with enclosure planning, I used SVG:
I used a public domain photo for this, here’s the full SVG for this:
Prepare Enclosure
I got into more details on how I do drilling in one of the previous articles, as well as on how to apply decal with inkjet decal paper.
I did not paint the enclosure, I just washed it with some dish soap after the drilling and applied the decal:
Final Assembly
I did soldering exactly how I planned it in the diagram above. Similarly like before – I soldered them based on height, from smallest (jumpers) to biggest (electrolytic caps and LED).
One note: I soldered socket for the TL072 in place first and I just popped the chip in. I don’t do that all the time, but benefit of doing it is that it saves the chip from being burnt from too long soldering.
Here’s how it looks like, practically 1-to-1 with the diagram:
Btw, Sparkfun has a good guide on soldering.
Since I had only PCB mounted pot, I had to cut it’s legs and solder wires to it:
Once I had the board soldered and pot attached, I could do some testing before the final assembly:
I hooked up crocodile clips to the wires coming out of the board and attached them to the jacks I used for breadboarding so I can try this out. I attached battery as well and everything worked as expected.
Despite more components and more complex board, everything fit more neatly than before 😉, looks like after few attempts at this small enclosure I’m getting there. I can probably make it neater if I put everything onto a PCB … there’s an idea!
Here’s the finished result:
Test Ride
Here’s the pedal in action:
Pedal in action:
