Sony PCG-GR300 Manual

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Connecting a CD player, active speaker, or an amplifier 
Use the optional port replicator to connect a CD, MiniDisc, or audio cassette player to the LINE IN jack and experience
higher quality audio. You may also take advantage of audio output sources and connect an active speaker or an amplifier to
the Headphone jack on the notebook. 
  Connecting an Audio Device to the Port Replicator 
Without the optional port replicator, simply connect an audio output device to the Headphone jack on the notebook. 
  Connecting an Audio Device to the Notebook 
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