Measuring voltage from the aux cable signal

Question

I wanted to make a bjt amplifier circuit to get used to analog circuit design. My plan was to use an AUX cable connected to my phone. I cut the cable and stripped the 3 wires inside. I wanted to see how much voltage it generated so I plugged it into my phone, started playing a bass boosted song to get better results and tried to measure the voltage with a voltmeter but I got nothing. Then I used a terminal block, I don't know if it was the best choice for this application but I inserted the cable from one side and put a jumper wire on the other side and screwed it in. It looks good. I connected it to a resistor and tried to measure it but again no result. Is the voltage too small to measure or did I do something wrong during assembly. (I didn't use the green wire on purpose)

Answer 1

1. The wires from the headphone are insulated. The green and red stuff on the wires is a kind of lacquer. It insulates the wires to prevent short circuits. You can't really remove it mechanically. You usually dip the ends into molten solder to remove the lacquer and tin the wire at the same time. Once the wire is tinned you can make reliable contact with your screw terminal.
2. AC voltmeters don't do well measuring audio. Most typical multimeters can only work with frequencies well below 1000 Hz.

You would do better to look at the signal with an oscilloscope.

Answer 2

You should measure between tip and sleeve, or first ring and sleeve, to get the left or right audio signal.

If you measure between the tip and first ring you will be measuring the difference between the left and right signal, which will be a much lower voltage than either the right or left signal alone.

The phone may be "smart", and not send anything to the headphone jack unless it thinks there is a headphone connected.