PDA

View Full Version : How to get a "line out"




MattG
Oct 17, 2007, 12:00 PM
I'm trying get a line out from my iPod -- that is, just a signal to send to an amp, without the gain added by the headphone jack. What's the best way of achieving this? Do I need the dock, or is there just a special cable or something, etc.? This is for a 160gb Classic.



mkrishnan
Oct 17, 2007, 12:03 PM
I think, FWIW, you have it backwards. Line out is amplified in comparison to headphone signals. That's why, when you use the headphone line into a receiver, amp, etc, you have to turn it up much farther than you would otherwise.

A dock is probably the most expedient way, as you can also use it to let the iPod stay charged and run off wall power. Sendstation makes another option (http://www.sendstation.com/us/products/pocketdock/lineout-fw.html) if size or portability are concerns.

http://www.sendstation.com/us/products/pocketdock/images/r_ipod_pd_lineout.jpg

EDIT: You probably want the USB version (http://www.sendstation.com/us/products/pocketdock/lineout-usb.html), sorry, but same idea.

bartelby
Oct 17, 2007, 12:05 PM
Line out is the lower of the two.
Line level goes to the headphone amp.

MattG
Oct 17, 2007, 12:07 PM
K that makes sense -- thanks guys!

mkrishnan
Oct 17, 2007, 12:33 PM
Line out is the lower of the two.
Line level goes to the headphone amp.

Sorry, I guess I should have been more clear. A headphone amp for studio headphones (that need relatively a lot of power) takes line level input and outputs a level of power suitable to the headphones. But the typical output of a headphone / earphone jack on a consumer device like an iPod is weaker than line level, isn't it?

bartelby
Oct 17, 2007, 12:35 PM
Sorry, I guess I should have been more clear. A headphone amp for studio headphones (that need relatively a lot of power) takes line level input and outputs a level of power suitable to the headphones. But the typical output of a headphone / earphone jack on a consumer device like an iPod is weaker than line level, isn't it?

There's not a huge amount in it, to be honest, but running an iPod from the headphone socket to the line in of another amp can overdrive the input stage and lead to distortion.

Le Big Mac
Oct 17, 2007, 12:42 PM
I think, FWIW, you have it backwards. Line out is amplified in comparison to headphone signals. That's why, when you use the headphone line into a receiver, amp, etc, you have to turn it up much farther than you would otherwise.

A dock is probably the most expedient way, as you can also use it to let the iPod stay charged and run off wall power. Sendstation makes another option (http://www.sendstation.com/us/products/pocketdock/lineout-fw.html) if size or portability are concerns.

http://www.sendstation.com/us/products/pocketdock/images/r_ipod_pd_lineout.jpg

EDIT: You probably want the USB version (http://www.sendstation.com/us/products/pocketdock/lineout-usb.html), sorry, but same idea.

Sik makes something similar.

Blue Velvet
Oct 17, 2007, 12:42 PM
But the typical output of a headphone / earphone jack on a consumer device like an iPod is weaker than line level, isn't it?

No, but because of impedance mis-matches, if you plug the headphone output into a line-in, you're going to get noise, attenuation and treble roll-off.

Headphone out = usually milli-watts into 16-32 ohms, line-in = 600-2000 ohms at 0.7 volts (I think).

Plug some headphones into a line-out and you're going to hear very little.

bartelby
Oct 17, 2007, 12:43 PM
<knowledge>

Do you know everything?:)

Blue Velvet
Oct 17, 2007, 12:47 PM
Do you know everything?:)

Oh yes... ;)

Nah, just some random neurons firing their last sparks from a previous life of running a little studio at school. Me and my TEAC 4-track; good times.

mkrishnan
Oct 17, 2007, 12:47 PM
Headphone out = usually milli-watts into 16-32 ohms, line-in = 600-2000 ohms at 0.7 volts (I think).

Hmm... I guess that makes sense, although you're mixing your units. :p

It does work reasonably well the other way around -- you can't plug headphones into a line out, but you can plug a headphone out signal into a line in. Typically if you output at 75-85% of the device max output (but not 100% for some devices, particularly the iPod), and you increase the gain on the amplifying device slightly (maybe 20%-30% more than normal) you get reasonably clean amplification, given all the limits involved. In a crucial application though, certainly you want a device that gets the iPod's line-out signal from the dock connector.

Blue Velvet
Oct 17, 2007, 12:49 PM
Hmm... I guess that makes sense, although you're mixing your units. :p

I know. I left it for you to work out the voltage... ;)

mkrishnan
Oct 17, 2007, 12:56 PM
I know. I left it for you to work out the voltage... ;)

Thank you, Ms. Velvet. :)

notjustjay
Oct 17, 2007, 02:11 PM
line-in = 600-2000 ohms at 0.7 volts (I think).


RMS or P-P? :p

Blue Velvet
Oct 17, 2007, 02:14 PM
RMS or P-P? :p

RMS, natch. ;)

MattG
Nov 1, 2007, 07:25 AM
Okay so excuse my ignorance but...I just bought a dock. Now I'm listening to my headphones, which are plugged into a headphone amp, which is plugged into the line-out from the dock. The volume control on the iPod still works! I thought the "line-out" would just send a signal. That being said, should I use the line-out with the volume cranked all the way up? I'm confused :confused: