Build an Audio Probe box

Jul 28, 2022 | General Pedal Building

If you’ve a broken pedal or a build that just isn’t working as it should – an audio probe is an invaluable tool to have – and it’s also super easy to make!

A note of caution: Some pedals have serious voltage inside – they may only take 9V DC in…but can up that voltage inside, so unless you know what you’re doing and can read a schematic – play safe and leave it to someone who knows how (drop us an email for a pedal repair!).

How to make an audio probe

We’ve called the ground BLACK and the audio probe RED – to makes things easier to follow!

The audio probe has 3 connections.

  • Output jack to amp
  • Ground probe/clamp (BLACK)
  • Audio probe (RED)

Here’s a list of parts you’ll need to build our version of the audio probe box (others are different, others maybe better, others maybe worse – this is ours – build it if you want!) – you can build this with just 2 wires into your favourite pen if you want…be we’ll be making ours in a box!

  • 1590A Hammond Enclosure
  • 1 Mono 1/4 Inch Jack Socket
  • Stereo connectors (see the pic below)
  • 100nf 100V box or ceramic capacitor (use at least 100v to be safe, this is for blocking any DC current)
  • 1 Crocodile clip
  • Wire or Multimeter probes
Buildin an audio probe with Five Cats Pedals

It’s a really basic build, 3 holes and 4 connections!

Drill a hole in the one end of the enclosure (for the jack – usually around 10mm).

Drill 2 holes in the top of your enclosure to place your connection points – drill these based on the probe connector type you have chosen.

Now insert your probe connectors and jack.

Next we need to create the connections, so solder a cable from the sleeve of the output jack to the ground (black) probe connectors. Solder a small length of wire to either end of your 100nF Capacitor and then connect one end to the tip of the output jack and the other to the audio probe (red) connector.

With that done – now you can connect your probes to the probe connections – you can use what you want here, we’ve opted for a cable with a crocodile clip for the ground (black) and a plain old wire for the audio probe (red) (with a tinned end).

How to use an audio probe

Insert a cable into the IN socket of the non working pedal, this is a lot easier if you connect a looper or mp3 player – as it saves you having to strum the guitar whilst trying to debug the pedal.

Don’t connect anything to the OUT of the non working pedal – that’s where the audio probe comes in to play. The audio probe forms the connection between the non working pedal, and the output jack of the audio probe box.

Connect a standard instrument cable to the output jack on the probe, then connect this to your amp, then connect the ground probe/clamp (black) (we suggest a wire with a crocodile clip on) to the ground of the non working pedal (usually the enclosure, or you can find a ground point using your multimeter).

Ensure you have power going to your non working pedal and it’s engaged.

Now press play on your looper/mp3, so the signal is going into the non working pedal, you can now begin to use the audio probe (red) to trace the audio path (this is far easier to do if you follow the schematic – most schematics can be found with some googling!).

You’ll get a signal going to the amp at the working points of the circuit when you touch them with the probe, when you come to a connection/component that doesn’t give any output that should – make a note of where/what that component/connection is – that’s your starting point for finding what’s wrong in the circuit.

Depending on what component/connection is faulty – you may have to resolder it or replace it then retest. If you have a signal at the previously broken component/path – try holding the audio probe (red) to the tip of the output jack on the non-working pedal – if you get a signal you could have just fixed your issue!

If you don’t get a signal just yet at the output jack…continue following the audio path using the schematic to get to the next broken component/issue and repeat the process above.