Weird audio voltage

[starplayer]

Hello. I'm trying to build a simple transistor amplifier which I know usually suck, but it's just for the experience.

Anyhow, after figuring my amplifier doesn't work, I tried measuring the voltage that is coming from my computer audio jack which is enough to drive a pair of 32 ohm earphones, the ones you plug in your ear. However, the voltage I get is very low, about 20 mV at maximum volume. I'm generating a sine wave at 60 Hz and my multimeter is TRMS, so I believe that should work. On the internet people say the voltage should be about 0.4 V, or even 1 V maximum (2 V peak to peak).

Is my multimeter just bonkers or is this normal?

[Yansi]

Probably you measure it wrong.

Usual audio levels for consumer electronics are about -10dBV which is about 300mVrms, for professional equipment it is around 0dBu (0,775Vrms) up to +4dBu (1.5Vrms) for long-distance cabeling.

Decent soundcard can output at least those 300mV.  What was your exact measurement setup? What amplitude of test signal (on the digital side) did you use? Was the card's output loaded somehow?  With 32R load you will sure get decreased voltage, the output impedance can be anything around let's say 100 ohms.

[IanB]

Are you sure you didn't damage the audio output from any previous experiments?

Assuming you didn't, you should get an AC signal in the order of 1 V RMS, which is sufficient to drive headphones at decent volume.

Try a higher frequency than 60 Hz. The output amplifier may be rolling off lower frequencies, especially if it is a lower quality audio source rather than a high quality sound card. Try 200 Hz or so.

[Simon]

How about 1KHz as pretty much most things are specified at 1 KHz

[IanB]

Playing regular music, the headphone socket on my sound bar is producing ~400 mV AC at maximum volume.

[starplayer]

Hey guys thank you for your answers.
I figured it out, I should have said the audio out was from my laptop. When I measured the line out of a sound system (to be used with big headphones), I measured about 400 mV. Turns out laptop jacks really output low voltages.

[Simon]

laptops will have the same output as PC's as they have to drive the same headphones.