My wife has a 20GB 4th gen iPod, and would like to use it in her car. I've already installed an auxilliary input to the CD player so she can plug it in, and this works reasonably well with the iPod's headphone output connected to the aux input. However, even with the iPod volume turned up fully, the volume on the car CD player has to be turned up quite a long way, with the result that when you switch it back to radio, you get deafened.

I'm thinking that the input impedance of the CD player's aux input is probably sufficiently high (I guess it must be at least 10kOhm) that the iPod headphone output (which is presumably designed to drive a low impedance input) is not able to deliver enough signal level, and was thinking that maybe the iPod's line output via the docking connector might be more suitable. But before I go to the expense and bother of buying the connector and making up a special cable to connect the iPod's docking port to the aux input, I'd like to confirm what the specs are for that output. The so-called technical specs on Apple's website don't give any of this data, so now I'm hoping someone here knows the voltage level and output impedence of the iPod's docking connector.

I'm afraid I can't help with the actual specs of the line out, but with my 4G 20GB iPod connected to my Symetrix 304 headphone amp (10K unbalanced input impedance), the headphone output at maximum is slightly louder than the line out from my SendStation PocketDock.

I've always used the line out in my car, and when it's connected to the aux input of my Nakamichi CD-45z head unit (lost the manual, so I don't know its input impedance), the level from the iPod is nearly the same as the level from the Nak's CD player (only 2 or 3 clicks lower on the volume control which ranges from 0-60).

OK, thanks for the info. It sounds like the line out isn't going to deliver any higher signal level than the headphone socket, so I think I'll not bother making up a special cable for it.

Cheers,
Clive

I use a SIK line out to my Amp at home & also to headphones through a volume control. I find the O/P a lot higher than the headphone O/P.

I mounted a dock in my car to connect the iPod, and am using the line output on the docking station. There is definitely some form of difference on my 3rd Gen unit, as I've noticed the following:

Connecting the headphone jack to the stereo (even my home stereo) results in much what you describe, I have to crank the volume on the iPod all the way up, and even then it's quiet at best.

However, using the line output, on both the home stereo and the car stereo, the output is much louder and I do not have to give it nearly as much volume boost on the head unit/amplifier to get the same "loudness".

Oddly enough though, if I plug cheapo headphones into the line output on the dock, the volume level is way too low for listening, but they sound great on the headphone jack.

Anyway, for my unit at least, I get significant improvement by using the headphone jack for headphones and the line out jack for stereo hookups. It's weird, but I assume there is a reason for this that I don't quite understand yet.

The headphone-out is just a headphones-out whereas the dock-connector audio-out is a genuine line-out. Hence, the dock-connector audio output is exactly what you'd want if you want to connect your iPod to an external amplifier.

Companies making devices to hook up your iPod to your car (like this one: http://catalog.belkin.com/IWCatProductPage...duct_Id=186770) or home stereo sometimes advertise with 'better sound quality' because of the use of the dock-connector instead of the headphones-output. I think the topicstarter should get hold of an docking-connector plug, it is bound to give him better quality.