a ground "sniffer"?

[fosgate3]

I have read about using these to "listen" to the grounds used in car audio applications in order to detect a good vs bad grounding point. I was wondering how to make them. I know that they use a tape head (aka stylus) but im not sure on what to solder to where in order to make it work. Can anyone help?

PS if this is in the wrong area, im sorry. I put it in car audio since im using it for car audio.

[Perry Babin]

The device you described was used to detect electromagnetic noise and could tell you if there was electrical noise being produced in a particular area (near a control module or along a wire) but it couldn't tell you much about the ground.

The definition of a good ground will vary with the situation. In general, good equipment will perforn the same no matter the location of the grounding point as long as the grounding point has a sufficiently low resistance in the circuit back to the alternator case/engine block.

If you wanted to see the difference between the ground potential of two points, you could use a voltmeter but you would have to have significant current flowing through the ground to read any significant voltage (unless the ground path had significant resistance). This is a good way to see if your amplifier has a good ground. You would run it at relatively high power (playing at high volume) and measure the resistance between the ground terminal of the amp and the various points back to the engine block.

If you want to 'hear' the difference in ground potential, you can use a device like the Radio Shack Mini-Amplifier. Connect one conductor of the input to the head unit ground and the other conductor of the input to another ground point and you can hear the difference between two points. This is only marginally useful because the noise will vary with current flow and with the noise generated by the alternator.

What are you trying to do?

[j_dunavin]

ah those are fun to make... i made mine by using the head out of a tape deack, and then wring that to a cheap rca end. I then took the head and rca end and hot glued them to a small, narrow, peice of plastic, And than i heat shrunk that to make a nice little modual.
I also used the Radio Shack mini personal amp/ speaker. And hooked the two up by making a 3.5 mm to rca cable.
The only difficult thing is getting the polarity of the head right. It's also ok to tie the right and left channel together.
There should only be three wires on the head, four if the head is a recorder. One ground, one for left and one for right channel. Tie the left and right together and of course leave the ground sepperate.