Audio Probe

This is very simple yet very useful tool for debugging new pedals. You need one 1/4″ mono plug, one 100nF capacitor, alligator clip and some wire. Connect alligator clip to jack shield and 100nF cap to jack tip. When debugging some circuit connect clip to circuit ground and use other end of cap (or wire connected to other end of cap) to follow signal path through circuit. Plug the probe into amp and plug guitar cord to pedal input (pedal output stays unplugged). Make someone play guitar while you’re probing circuit and once you find a spot where nothing is heard through amp you found a possible problem.

Audio Probe

If you have a cap small enough you can fit into plug casing. It will look nicer and cap will be protected inside. It can be seen on this photo how I did it. If you can’t find any slave around to play guitar while you’re probing the circuit it’s not a bad idea to connect guitar cable to sound card output and just play some music on computer.

Audio Probe Photo

The other way to make this useful tool is using 1/4″ jack socket and regular guitar cable. Advantage over previous design is that you need shorter probe leads and you can use as long guitar cable as you need.

8 Responses to “Audio Probe”
  1. CirqCuts says:

    Nice. Not sure I have 63V caps, but I’d bet 50V caps are in the inventory. I figure that wouldn’t be an issue, no? Take care, Circ.

  2. Martijn Van Maanen says:

    What does the 100nF cap do?

  3. Hendysp says:

    Thanks a lot, its make me understand what is :audio probe, words that make me confused (before i read this nice explanation)

  4. Keith says:

    I just wanted to say as a fellow DIYer I love your sight and think you have a ton of usefull info. Bravo!!!!

  5. rock_mumbles says:

    Scroll down on this page and see the same concept used as an amp listening tool …

  6. Doctor Tweek says:

    This is such a cool tool. Costs next to nothing and lets you prod around and hear what’s doing what in your effect pedal. Great stuff and a lovely drawing. Best, Steve aka Doctor Tweek.

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    The idea behind this site is to share my experience with Do It Yourself approach to guitars, amplifiers and pedals. Whether you want to save a couple of bucks by performing a mod or upgrade yourself instead of paying a tech, or want to build your own piece of gear from scratch, I'm sure you will find something interesting here. Also, this is the home of DIY Layout Creator, a free piece of software for drawing circuit layouts and schematics, written with DIY enthusiasts in mind.