How to use an audio probe

[copperheadroads]

I just built an Audio probe  like R.G keen describes  using a .1uf 400v cap  & a guitar cable  & as is described ,my question is how do I use it ?
do the circuit have to be powered up ?
if i were to use a my looper pedal with my amp as my signal generator how will i hook it up .  I tried several different ways but i get hum from having the probe in my hand & it goes quiet when I touch a contact .  I must be missing something




   

[slacker]

The basic idea is you take the circuit that you want to test, power it up and play some signal into it, so in your case record a loop on your looper and plug the output of the looper into the input of the circuit you want to test. Plug the audio probe into your amp's input and turn the volume down very low to start with. Connect the ground lead of the audio probe to the ground of the circuit you want to test and then use the probe to listen to the signal at different points in the circuit.
Be careful with the volume on your amp some circuits will have very quiet and very loud signals and you don't want to blow your head off.

[Granny Gremlin]

https://www.youtube.com/watch?v=6dwsAhe63cw#t=195

(tube amp vs pedal but same process)

[mcknib]

Here's a link that may be useful also contains a link to tracing the audio path

http://www.guitarpcb.com/apps/forums/topics/show/4814011-using-an-audio-probe-to-debug-builds

[MrStab]

it's much better to use a spare jack with a plastic covering instead of a lead IMO (see: "enhanced version" here: http://www.diystompboxes.com/pedals/debug.html ), as you don't have to make or cut a whole lead, you can change the lead length at will, it's easier to avoid touching bare wires/terminals, the cap wiggles around less and it's easier to store. seeing how you've already made it though, i'm probably too late!

[GibsonGM]

I used an old plastic totally enclosed jack from a DOD Super Metal Pedal I cannibalized years and years ago, IIRC.   Another one was a stereo jack; I had TWO probes + ground, and TWO outputs to TWO amps. That wasn't so great; PITA to use and didn't add much value to the process, IMO.   

Don't forget the cap!  And maybe use one with a nice, high rating so that one day you can safely use your probe on a tube amp which may have much higher voltages...but if all you have is low voltage, just use and, and maybe put tape around the jack labeled "<16V" or something, depending on your cap. 

[Kipper4]

I used old hifi speaker cable jack on one end of the wires 
at the business end I used an alligator clip for the ground connection.
I used an old felt tip pen gutted it, fed some thin mig welding wire through with a cap soldered to it and the other end of the wire to it. feed the cap into the pen body and hot melted both ends.
so now i can probe on the breadboard and just stick it in the board holes where needs be.
bonus is i dont have to worry about shorting pins on an ic or transistor when probing because the probe tip is about a mm wide.
Boooom

[MrStab]

I used an old felt tip pen

nice! so like an actual DMM probe. that sounds a lot less annoying than flimsy terminals or wires. get that patented!   

[PRR]

> get that patented!

The idea of using a BIC pen case goes back many decades.

Before that we stuck a bolt in the end of a pill-bottle. Not as slim but a good grip. For extra cleverness we soldered a needle to the bolt. You can also shove a long needle through a cork and solder a lead to the eye of the needle. (This assumes you buy wine with corks, which I guess is less common now.)

[MrStab]

in that case, i amend my suggestion:

get sued!

[nosamiam]

I just use 2 alligator clip test leads and an instrument cable and it works great.

1) Plug one end of cable into the amp.
2) Open the jaws of one alligator clip lead wide and close it on the sleeve of the other end of the cable. The alligator clips I use have a "notch" in the back of the jaw that holds it on the sleeve really securely. Clamp the other end of the lead to any ground point. I usually use output jack.
3) Clamp one end of the other test lead to the tip of the cable. Because of the shape of the tip, it stays on fine. Clamp the other end to the cap and you're good to go.