Analog Tone & Probe with Amplifier Troubleshooting

[jdak907]

Hello,

I thought that using an off the shelf analog tone generator and test probe might be useful for tracing amplifier circuits. My intended use is on vacuum tube and solid state audio amplifiers, injecting a tone at the input or some intermediate stage of the amplifier and probing along the circuit. Has anyone tried one of these or have any insight on what I am proposing? They really don't offer much information in regards to the specific application I have in mind, but I don't see why it couldn't be used for this.

Here is one I was considering:
https://www.lowes.com/pd/Fluke-Networks-Analog-Tone-and-Probe/3438412

Thanks!
Jeff

[flynwill]

Those devices are intended for tracing communications wiring.  They will not be of much use in trying to debug stereo amplifiers.  For that you need a normal signal generator and an oscilloscope (and a schematic) for the device you are debugging.

[jdak907]

I understand what their designed application is, however I don't see any difference in function for tracing audio amplifiers - but I don't know what I don't know. Can you explain why it wouldn't work? I am looking for an audio signal trace... basically inject a tone into the input and check the output stages of amplification devices or certain points in the circuit where there could be noise injected or degradation of signal. I'm looking to use this like a "non-contact" probe.

[commongrounder]

Tone and probe sets are designed for tracing passive, unpowered, wires and cables.  The toner signal is relatively strong to cause the wire to radiate an electromagnetic field that the inductive probe can pick up. You really want contact probing for doing signal tracing in amplifier circuits.  Inductive tracing will end up leading you on wild goose chases. In theory you could use the toner as a simple signal generator, but you might need to pad the output in some applications to avoid overloading the input stage.

[floobydust]

Instead, inject audio and use a signal-tracer, a small audio amp with say an LM386 and speaker.
You can hear various distortions, lack of bass, loss of signal etc.
This is what we used in the electronics repair shop and it works fine and fast to localize problems.

Otherwise, injecting a tone requires you use a scope to inspect the signal.  A 1kHz sine and square wave can sound similar yet mean a huge difference when troubleshooting.