- July 12th, 2013
- Write comment
Out of all the electronics projects I’ve been involved with lately, the construction of audio effects seems to be the most satisfying endeavor yet. Using the Karaoke Party schematic thanks to the “sharing is caring” DIY ethos of devi ever : fx, I was able to build this as my first guitar pedal, which you can see a video demo for along with details on construction after the jump.
To start out, I first needed to build the effect in prototype form. This required a protoboard to easily connect components along with the power supply I built earlier. Also, I needed to solder short lengths of hookup wire to the connection points on the audio jacks and potentiometers so I could have more versatility in the placement of connections. The other connections for various points were initially made using the same green hookup wire, but shortly after I discovered the wonders of using color-coded banana plugs for this instead.
After double checking my connections for accuracy, I dialed in just over 9V on the power supply using my multimeter and hooked it into the power rails for the prototype circuit. Plugging in my cables, I flipped the amp on and held my breath. To my delight, nothing blew up and I actually heard the desired effect while playing my electric guitar through it.
Hearing the effect work definitely felt like a mindblowing achievement, but I still knew there was work to be done for this to be converted into an actual guitar pedal. The next step was to try connecting a 3PDT bypass switch and LED indicator.
Using some more online tips, I was able to get this going so that it went into true bypass when the switch was pushed to turn both the effect and LED off. During this process, I also noticed how different color LED’s require different resistance values to alter their brightness.
Now that I had everything working in prototype form, I began fitting audio jacks, control pots, a DC jack, UV LED and 3PDT switch into the pedal enclosure. I didn’t start soldering the hookup wire to this gear until I had built the circuit, since having that gave me a better idea of the wire lengths needed. I also opted to use the many ground connections available on the PCB rather than attempt a “star-ground” coming from the DC jack negative terminal, as some pedal builders recommend.
The actual circuit was built using my prototype and the Karaoke Party schematic for reference, pushing the MPSA18 transistor, two .1μF (104) capacitors, and six resistors of sizes ranging from 10kΩ to 3.3MΩ into a through-hole plated perfboard PCB and bending the leads in such a way that they could be easily soldered to both the board and each other. I then painstakingly soldered these component leads point-to-point.
Now that I had the circuit ready, I knew both how long to measure the hookup wires to the enclosure gear as well as the available ground points left on the PCB. After cutting and stripping each wire, I would solder one end first to the contact points inside the enclosure. I also connected the LED in series with a 1kΩ Current Limiting Resistor (CLR). Once every contact point inside the enclosure had the right wire soldered to it, only then did I start connecting the circuit, since all the wires were cut fairly short to save space.
Once everything was connected, the time came to see if it worked, and it did. I did some final touches before screwing the back plate onto the pedal, mainly clipping excess leads from the circuit and applying some hot glue to hold it in place so that it would not accidentally short to ground from touching the metal enclosure. Being my first pedal build, I spent many hours carefully working on it to avoid having to backtrack in such a compact device. I probably should have tested the circuit before connecting it to the enclosure, but I had been so careful that I felt confident enough to skip that step. To me, the most important factor seems to be careful planning so that you do everything in the right order for least difficulty in handling the assembly.
If I could go back and change something about this build, it would probably be to make the CLR a higher value so that the LED would be less bright. I am looking forward to getting more into the aesthetics and visual design of pedals, since this project was mainly focused on the technical aspects of pedal building. This was a fun exercise, although for the most part I would prefer not to build circuits point-to-point as it is fairly time consuming compared to using a properly made PCB for a certain circuit. I feel more confident working on electronics for audio after this and am thrilled to explore where this will take me next.