DIY Sound Probe

When it comes to pedal circuits that give me grief, usually standard troubleshooting, solder bridge finding and "oops, I'm an idiot" admitting will suffice. In the case of my Blues Driver and Kay tremolo clone circuits these methods just aren't good enough, apparently. Both circuits function well, but have their own mysterious issues that ruin the functionality of the circuit entirely. This is why I decided I needed to construct myself a sound probe and see if that could get me anywhere closer to figuring out the problems.

A sound probe is simple enough to build. You take a length of double wire and on one end you solder on a clip for your ground, and a probe attached to the other wire. On the other end you connect the ground and probe wires to a male audio jack of your choosing, using a 100nf capacitor on the probe end, and you're good to go. I chose 6.35mm so I could plug into my mini amp. I've had some really thick car audio wire hanging around for a while, so I took about a foot of that and slapped my audio probe together. Quick and dirty, but it works.

To use the audio probe I plug it into my mini amplifier, attach the clamp to the (hopefully) grounded enclosure of the circuit and start probing along the circuit board to find the signal path. Don't forget to inject a signal into the pedal circuit first, or there will be nothing to hear. To do this I chose to play music from my cellphone and used a 3.5mm to 6.35mm adapter to connect a guitar cable between the input jack of the circuit and output of my cellphone. This all worked pretty well.

Despite having one more tool in my arsenal to help troubleshoot circuit gremlins, I'm still no closer to figuring out what's wrong with the Blues Driver clone. However, it took me posting on reddit to find out the tremolo circuit was bad from the beginning. I could go on and on about how so called verified layouts can still yield absolute worthless results, but the counter to that usually ends up being that I need to be Nicola Tesla to even touch a circuit. Reddit is a weird fucking place. Once the volume issue on the tremolo was corrected I still need to figure out why it distorts. But that's for another day.

Ugly but functional!