What does this specification mean?

[infoseeker]

I was looking at an Alpine head unit owner's manual and found this spec.

"maximum pre-out voltage: 2 volts/10k ohms"

What does it mean?

Much thanks, in advance.

 

[theAnonymous1]

It means with an input impedance of 10k the pre-outs will have a "maximum" output of 2v. Who knows what their definition of "maximum" is; hopefully they mean RMS.

 

[infoseeker]

Could you explain in more detail?

Thanks.

 

[jol50]

Likely a 2v deck. Mine says the same thing and works fine just like all the rest of the 2v HU I have run. It supposedly means if you turn it all the way up into 10kohm load you should get a max of 2v output. I think it is rms but I am not certain. Right now I don't even turn my alpine up half way because the volume works a lot faster that way.

 

[infoseeker]

I ask because, if my memory serves me correctly, I remember seeing 1.6 volts AC RMS on those outputs, before clipping. My testing was done with a Craftsman DMM that claimed an input impedance of 7.5 M/Ohm. If that number is correct, that should be more than sufficient to receive an accurate reading. Do you think I would receive a more accurate reading with a Fluke DMM or are thos outputs just overated.

 

[Travis Clarke]

My question would be, how did you test that voltage level using your multimeter since it's an AC signal?

Normally I run a test tone of some low frequency (say, 60-100 Hz or so) when measuring my head unit or amplifier output voltages. I do this using a CD or etc. with test tones.

You should be able to get an "accurate enough" measurement under the right conditions with a decent multimeter.

But one thing my career in engineering has taught me is, you are right to measure it and not just believe everything you read!

 

[infoseeker]

Good point. I used an Autosound 2000 CD#104, track 10, which has a 1kHz @ 0dBFS ac signal, then measured the output on my dmm on the ac volts scale. The 1.6 volts ac is clean signal as viewed on the screen of an o'scope. Anything pass 28 on the volume dial - above 1.6 volts ac - was a clipped signal which I didn't take into account in my measurement. Maybe 2 volts out yes, but only 1.6 volts ac of it was useable.

Thanks for the response.

 

[Perry Babin]

With the scope set to 1v/div, a 2v RMS signal would extend from -2.8 divisions to +2.8 divisions.

http://www.bcae1.com/temp/P10101162rms.jpg

You should also use a lower frequency. Many meters have a very limited frequency response and 1k may be out of the range where the meter is accurate.

 

[infoseeker]

Thanks, Perry, I agree 100%. I checked the frequency bandwith on the AC volts scale and 1K is outside of the useable passband. It reads up to 40 - 400 Hz on the AC volts scale.

So, the reputable company Alpine is, I would think that deck would, indeed, output the 2 volts. But I still like to check.

Thanks for all the response.