Audio probe not probing all the time..?

[philbinator1]

As an aside to my crying like a baby (yuk yuk) about my wah/transistor problems, I recently built an audio probe
and tried probing my wah with it...I started from the input and worked my way onto the pcb.  However I soon
realised that while some points emitted the beep (440 Hz generated from my metronome) others didn't?!  Is this
standard behaviour for circuits?  I had the wah "on" and I thought that all of the solder points would emit a beep?

Any help appreciated!

[Top Top]

Some of the points on the circuit do not deal with audio, but rather with voltages to regulate/power the other components on the board.

Also at some points, there may be DC voltages mixed in with the audio, which can interfere with a proper audio signal - capacitors are used at points in the circuit to filter the DC voltages out.

So in short, it is normal that not all points on the circuit will have the audio signal that was present at the input.

[John Lyons]

On thing that helps keep your sanity is to use a CD player to provide the signal.
Nothing more maddening than a steady beep or tone. Granted you need a steady
tone for some testing but to follow a signal...

You can also record some guitar playing and run that through the pedal which is
next best to playing though it yourself.

Just an aside.

John

[philbinator1]

Hey thanks for that guys!  Good to get the beep issue clarified, and yeah I will at some point plug in the CD walkman
cos the beep gets boring pretty quick.

cheers, you guys rock   

[GibsonGM]

Luckily, my CD player cuts the speakers when I insert a plug in the headphone jack. So I never heard my 20 minute classic compilation of 1KHz, 220Hz, and 440Hz going all the time, until I actually probe!!  I like using the sine wave bc it is constant and easy to set up the correct input levels, but music should work pretty well too, esp. some extended chord strumming. 

[petemoore]

  You have to be careful what you touch your finger to.
  Otherwise, the sound of thumbuzz [touch the end of a 'live' cable] is something I'm real familiar with. It varies of course with different amps and settings, but is a very reliable little audio-injector.
  As John mentioned, a CD or any other source [toy electronic keyboard with a key taped or weighted down] which you can ''inject'' [input] a signal source where you like [basically the opposite of the audio probe, which 'extracts' signal output> to an amp].
  The probe or injector capacitor, just blocks DC [unless small value enough, then it starts rolling off the bass.

[philbinator1]

But, if some solder points don't carry audio and just dc, how can you test those points?