headphone jack to line level

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headphone jack to line level

Post by paulrevelcet » Fri Nov 04, 2005 2:23 pm

what's the best way to plug a headphone jack into a line level amp? I want to plug my ipod into my car stereo system and since my amp has an extra couple of rca jacks, I know I could just keep the volume down on the ipod but I cant trust the rest of the family. Is there a good web site that has the specs on all the different types of inputs and outputs? thanks for your time.

Michael J
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Re: headphone jack to line level

Post by Michael J » Fri Nov 04, 2005 3:01 pm

You may find you need to run the iPod flat out
just to get enough volume to hear it at a reasonable level.

The output on most of these MP3 Players is in
reality very low, afterall you are virtually
placing the speaker inside your ear canal.

A Flea in there sounds like a herd of Elephants.

Most of these units run an output of 32 0hms.

I have a Lexar LDP-600,512 which I have sometimes
run straight into a set of PC speakers w/sub.

I need an Eleven or Twelve on the MP3 volume control,,~ ;o(

Some car stereo (Hi powered) gear needs 2 or 3
volts line in to work. You may end up needing a booster.

Apple probably sell an overpriced attachment for
this purpose.

<small>[ November 04, 2005, 03:05 PM: Message edited by: Michael J ]</small>

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Re: headphone jack to line level

Post by sofaspud » Fri Nov 04, 2005 5:05 pm

The user's manuals for your ipod and car amp should have the input & output specs.
I recommend that you build yourself a battery-powered preamp to go between the mp3 player and power amp. Even one based on a pair of LM386 ICs will work fine - 20X gain is plenty.
I use Lafferty's "Headbanger Headphone Amplifier" (Do a search for that. I think it can be found at headwise.com.) for my mp3 player-to-car stereo connection. I made a few modifications to mine and it runs quite a long time on four AAA cells (6V).

<small>[ November 04, 2005, 05:09 PM: Message edited by: sofaspud ]</small>

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Re: headphone jack to line level

Post by samcog » Fri Nov 04, 2005 5:45 pm

Try a simple L-Pad network of a 100K resistor in series with a 10K on the output with shield or screen as a common ground to both. If this is a too low of a volume try adjusting the series resistor. Or just use a dual 100K pot. (I assume you are interested in stereo.)
I hope the above diagram shows up correctly. If not, E-Mail me and I'll send you a BMP drawing.

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Re: headphone jack to line level

Post by Enzo » Fri Nov 04, 2005 8:54 pm

Identify the problem, then solve it. Play typical material in the Ipod and measure the signal level. That voltage is what you have to work with. For example 1/8 watt across 32 ohms is about 2 volts. But I have no idea what power earphones produce.

The inputs to the power amp or other preamp should be high impedance, so they shouldn't load it down any. What level of signal does the amplifier want to see?

If the Ipod produces higher voltage than you need, a simple voltage divider or classic "volume control" should work. Slap a 10k or 50k pot across the ipod and dial in the level you need. Or make a fixed divider with resistors.

If the ipod produces less signal than you need, then a small dual op amp configured for a few db gain should boost you up to where you need to be. You can establish signal levels in that circuit to suit your taste.

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