1
\$\begingroup\$

I am trying to build my own distortion pedal. I initially built this on a breadboard and connected it to a 9V power supply and it seemed to work fine when I connected it to my electric guitar. So I decided to solder it to a prototype PCB board. The ground and live wires are connected to a 2.1mm barrel jack and is then plugged into a 9V power wall adapter. But for some reason every time I try to power up the circuit board the live and ground wires between the 2.1mm barrel jack and the circuit begins to smoke and the plastic casing melts. I am unsure of how to fix this problem and I was wondering if anyone had any solutions? I've added the image of the circuit and schematic belowThis is the circuitthis is the underside of the prototype boardthis is the circuit for the pedalHere is the schematic for the pedal

\$\endgroup\$
3
  • \$\begingroup\$ the wires to the controls should really be on the other side of the board \$\endgroup\$
    – jsotola
    Commented Oct 25, 2020 at 18:42
  • \$\begingroup\$ In the second photo, I see a solder bridge between the where the red and black wires connect to the board - a direct short circuit on the power input. As others indicate, you will have many other short circuits on the board because you didn't cut any of the copper strips where you don't want connections. \$\endgroup\$ Commented Oct 25, 2020 at 19:37
  • \$\begingroup\$ Did you remember that standard guitar pedal power adapters are wired "backwards", i.e. the barrel = positive, tip = negative? \$\endgroup\$
    – td127
    Commented Oct 26, 2020 at 0:10

2 Answers 2

2
\$\begingroup\$

For a start it appears that you have forgotten to cut the traces between the pins of the chip. That means that pins 1 and 8 are connected, 2 and 7, 3 and 6, 4 and 5. They shouldn't be.

enter image description here

Figure 1. A Vero tool is rotated by hand to remove copper around any hole thereby isolating the strips either side of that hole. This tool doesn't go right through the board as in Figure 1.

If you haven't got one of those then a 3 mm drill bit twisted in your fingers will do the job.

Next you shouldn't really be connecting all the wires directly on the bottom of the board. Keep components and wires on the top side and at the edges. That way you'll be able to inspect it more easily.

enter image description here

Figure 2. Rather neat circuits can be built on Veroboard if the components can be mounted perpendicularly to the direction of the copper tracks. Here there are no flying wires and all cross-connections are done with components or wire links. Image: Wikimedia Commons.

Note that the links are all straight wires going across the direction of the strips. To get from one side of the chip to the other would take two links.

\$\endgroup\$
3
  • \$\begingroup\$ Thank you so much! I am still very new to creating circuits and this was the first ever time I've used a prototype PCB board and I never realised that I needed to cut traces. I am definitely going to get myself one of these tools. Also thanks for the tips on tidying up the circuit! \$\endgroup\$ Commented Oct 26, 2020 at 14:40
  • \$\begingroup\$ It's funny how your mind plays tricks on you. You expect the copper traces to conduct where you want them to but not connect when you don't want them to. Try laying out your board using one of the many protoboard+layout+tool+online options. In your case you might want to find one that handles off-board components such as your pots. \$\endgroup\$
    – Transistor
    Commented Oct 26, 2020 at 14:59
  • \$\begingroup\$ Thanks so much for your help! I'll definitely use one of these online tools next time I design a PCB board. \$\endgroup\$ Commented Oct 26, 2020 at 15:05
0
\$\begingroup\$

It's a very poor circuit for a guitar input (they need much higher input impedance) and there's no indication in your schematic that you have connected power rails to the chip. Also, the TI version of the TL082 does not state that it will run from a single supply of 9 volts: -

enter image description here

I can't see cuts in the copper tracks that would prevent opposite pins of the TL082 shorting. Neither do your photographs indicate how the back-to-back diodes are connected to the chip.

On another note, your tone control will cause the op-amp to oscillate if wound to close to one end i.e. it would place a 22 nF capacitor on the op-amp output and that's usually a recipe for disaster.

In short, your design looks poor and your implementation also looks poor and very suspicious.

\$\endgroup\$
4
  • \$\begingroup\$ I agree that the circuit has problems and the wiring is a mess. \$\endgroup\$
    – Audioguru
    Commented Oct 26, 2020 at 1:07
  • \$\begingroup\$ Thanks so much for your help! This is my first time using a prototype PCB board, and I definitely still need to work on my implementation and making the circuit look tidier. I took the design from the internet as I am not yet experienced enough to design my own circuits but I'll definitely do some more research for a better design, thanks! \$\endgroup\$ Commented Oct 26, 2020 at 14:45
  • \$\begingroup\$ @FraserHolman when you do find another schematic just post here before building. \$\endgroup\$
    – Andy aka
    Commented Oct 26, 2020 at 16:19
  • 1
    \$\begingroup\$ That would be brilliant! Thanks @Andyaka ! \$\endgroup\$ Commented Oct 26, 2020 at 16:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.