making a simple audio probe

[smallsnd/bigsnd]

real quick for anyone building - it's important to have a simple audio probe laying about, especially in the absence of an oscilloscope. it can make the difference easy debugging and not being able to debug at all...

parts you need:
1 1/4" female jack (mono, but stereo will be fine as well)
2 alligator clips
1 cable
1 amp
a small clipped component lead or tiny screwdriver

first plug something into the input of the effect you're debugging. if you have a signal generator, oscillator, atari punk console, pedal that can oscillate, etc. then just use that so your hands are free. otherwise use a keyboard with a held note or just strum your guitar, bass, or whatever.

so take the 1/4" jack and figure out which lug is ground and which is signal, attach an alligator clip from the ground lug to your circuit's ground (or to the input jack, provided it's grounded), attach the other clip to the signal lug and leave the one end free, plug the cable from the jack into your amp, now probe around touching different spots on your circuit to hear what happens at each stage! (you may not hear things at certain points and you probably shouldn't be doing this with any high voltage effects as it may damage your amp)

here's a pic to help figure out which lugs are which on a jack. a mono jack will not have the "ring" lug, so just don't worry about that one for this application.

[stanimal]

Nice!!! And an awesome thing to post here for all our resident diy'ers...

I did something similar with one of those cheapo cables that came with my old epiphone Sheraton but instead I cut off one end and strip the plastic to expose the cable, then solder an alligator clip to ground and a capacitor (damn was it a .01uf..?? Damn my inability to retain numbers!!) to the positive.. Then plug the other end into your amps input and clip the ground alligator clip to the pedal ground and use the 2nd leg of the capacitor to touch each connection on the board following the schematic until you reach a dead spot...

I love this stuff I really do....

[comtrails70]

so how does the actuall debugging happen if you wont get a signal at some points on the board?
or is it at those points where the bug is?

(if that question sounds dumb its ok.. im a noob)

[smallsnd/bigsnd]

well, let's say there is no signal at the output of your effect.
let's use the fuzz face schematic as an example:


i usually start probing at the output and work my way to the input, but whatever works for you...

probe output, no sound. move to the connection the pot makes with the .01uf capacitor, still no sound. move to the connection the .01uf makes with the 8.2k and 330/470 resistors, still no sound. the 330/470 is connected to the power, so no need to check there (just make sure it is connected properly) move to the joint between the 8.2k and the collector of Q2, no sound. then move to the base of Q2 where it joins the 33k and the collector of Q1, sound! ok so the problem lies at the 8.2k/Q2 collector junction. there are only a few things that can be wrong here... either Q2, the 100k, 1k pot, or 20uf cap.

check the transistor and the capacitor orientation, check to make sure the pot is wired correctly, then see if there are any cold joints, solder bridges, broken things, etc at that point... none of those? look back and make sure all your component values are correct, power is wired correctly, etc. if it's something simple like no signal, one of those things will usually fix it! if there are other weird things going on, there may be additional sections of the circuit you'll need to address. at least you'll know where to start, though...

hope that helps and isn't too long winded!

[Jero]

hope that helps and isn't too long winded!

When it comes to things like this, long winded is very acceptable

[Scruffie]

This article may also be of use here... also shows the audio probe design and instructions.
http://www.diystompboxes.com/wiki/index ... =Debugging

[comtrails70]

this definitely save time/headache!thanks

[phantasmagorovich]

This is excellent!

I'll make this before I start building my first kit! That means: tomorrow.