You could probably do it passively with some small transformers. To get 
the output imp of the laptop, you might want to try various pc speakers 
with a known input imp until you find a good sounding match. Or, you 
could try the math route. Take a look at this site:

http://www.circuitsage.com/matching.html

Cheers

John

Mario Mendes wrote:

>Hi guys,
>
>Recently I boutght a second mp3player/walkman/laptop fm transmitter to
>be able to transmit music from my laptop in the house to a radio in the
>backyard. Just like the first one it does not sound good (this one is
>being returned).  Both transmit like they should, but the sound coming
>out of the radio speakers is really low, which leads me to believe that
>there is an impedance mismatch between the laptop's output and the
>transmitters input.
>
>The laptop's specs from the manufacturer do not list the output
>impedance anywhere and the manufacturer's web site was of no use for
>this either.  Googled for the same information but I did not find
>anything reliable as far as this info is concerned.
>
>Does anyone know what is the typical output impedance of a laptop's
>headphone jack?  The only usefull info I have found is that the majority
>of these jacks will put out 1v rms.  Also, not being knowledgeable in
>analog electronics (I do fine in with digital electronics though), can
>anyone help me out with coming up with an opamp circuit that would take
>care of this impedance matching?  Since this is for home use, I thought
>that a couple of opamps (1 left and 1 right) could take care of it with
>either a 9v battery or a simple power supply.  This would plug into the
>pc headphone jack and the fm transmitter would plug into it.
>
>Thanks in advance.
>
>
>-Mario
>
>
>  
>

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