Jul 11, 2008 at 6:09 PM Thread Starter

#### arande2

Hello I just measured the output of my A/V Receiver's headphone jack.

I don't have a good way to measure current, so I could only measure voltage. I would guess that the voltage capability drops at higher current levels.

First, I should state that I got a max voltage of .6 volts AC from my portable radio.

So.. I played a sine wave through the output of the headphone jack. At first, I kept it low. The first measurement was around 1.5v, not too high. Then I turned it up a few dB, a little over 3v. I started wondering how far it would go.

I turned it up 20dB, 30v. At this point, I was confused. 30v? So I turned it up to find a max reading of a little over 49 volts. I should note that past 40 volts, the measurement kept going down to 0v suddenly after about a second. I assume it's the internal protection circuitry.

49 volts? Why would it be able to put out 49v, even into the high impedance of a meter? What's a good way to get a more useful measurement?

One last question: Is it normal for headphone outputs on Hi-Fi Equipment to be able to put out such a high voltage?

Thanks much! I am eager to learn.

Jul 11, 2008 at 6:55 PM

#### arande2

Hello I just did a little more testing.

I made it so I could measure the voltage while the headphones were playing. Now I got .5v at the same level at which I got 20v. Aha!

Well anyway.. With heavy bass, I couldn't pass .6v without the drivers starting to act up (NOT good..) and go too far (this is 20hz). And with loud music (with them off my ears), all I could get to was .18v before they started hurting my ears. According to the specs, .18v is about 1mw, which is 115dB with these headphones. Yeah, they're sensitive. At 10mw input (deep bass), the pressure isn't too extreme, but oh well.

Anyway I have concluded that my headphone jack is limited to about .5v before it starts sounding bad at 33-ohms.

Jul 13, 2008 at 1:34 PM

#### arande2

Is it possible that the headphone output is the speaker amp connected with resistors?

That would make sense since the voltage drop won't happen with the meter's high input impedance. 49 volts.

Jul 13, 2008 at 7:31 PM

#### Uncle Erik

##### Uncle Exotic
Quote:

 Originally Posted by arande2 /img/forum/go_quote.gif Is it possible that the headphone output is the speaker amp connected with resistors? That would make sense since the voltage drop won't happen with the meter's high input impedance. 49 volts.

Yes, that's often the case with receivers. Very few of them have dedicated headphone amps.

Jul 13, 2008 at 9:00 PM

#### arande2

I suppose headphones with higher impedances could get more voltage in that situation.

Jul 13, 2008 at 9:13 PM

#### arande2

Yes I will order thousands and thousands of dollars worth of sports wear

Jul 13, 2008 at 9:19 PM