Or, simply make sure you have a proper ground connecting the two devices :-) But seriously, I believe the noise to be caused by the cheap amplifier in the computer, in conjunction with running a 0.5v line-in with a higher voltage speaker-out. KreAture ----- Original Message ----- From: "Dwayne Reid" To: Sent: Sunday, March 02, 2003 8:52 PM Subject: Re: [EE] Headphone out to RCA line-in converter > At 04:39 AM 3/2/03 -0800, Chris Rocco wrote: > >I would like to connect my laptop's headphone jack to my stereo's RCA > >input jack so that I can hear MP3's and video files on my stereo/TV -- > >the problem is that I get a hum when I use a direct cable, even when > >there is nothing generating any sound on the laptop. Is this due to an > >impedance mis-match? How can I fix it? > > Can you run your laptop from batteries only? If so, disconnect the power > cord and see if the hum goes away. > > Are you also connecting a video out from the laptop to the TV or anything > else? If so, disconnect those lines as well and see if the hum goes away. > > What you want to do is have ONLY the audio line from the laptop to the TV > connected - nothing else. > > If the hum persists, you have to find out if it is coming from the laptop > or the TV. Disconnect the cable from the laptop and see what happens. Does > the hum change as you move the cable and/or laptop around to different > locations? Try hooking up a portable (battery operated) CD player to the > TV instead of the laptop. > > On the other hand, if the audio is clean and quiet when the only cable > connected to the laptop is the audio cable, start connecting the other > cables back to the laptop one at a time to see what causes the hum to > re-appear. > > My best guess is that you need ground isolation between the laptop audio > output connector and the TV. The tests above just help to confirm this. > > The quickest / cheapest ground isolation fix is a pair of 600:600 audio > line transformers - one for each channel. The transformers are available > from a variety of sources - I can even supply you some if you need. > > > The transformers will most likely have 4 or 5 or 6 wires coming out. You > need to use only 4 of the wires on each transformer: ignore the center tap > connections if they are present. > > The easiest way to wire the transformers in is to cut the audio cable at a > location convenient for you - near the laptop end may be the best so as do > reduce magnetic field pickup from the picture tube (deflection & degauss > coils). Cut the cable and strip the ends. You should see a bare shield > covering the hot after you have removed the jacket. > > Simply connect the incoming hot & shield to one side of the transformer, > connect the outgoing hot and shield to the other side of the > transformer. Both channels have to be wired exactly the same to ensure you > maintain phase polarity. > > That should do it! > > dwayne > > -- > Dwayne Reid > Trinity Electronics Systems Ltd Edmonton, AB, CANADA > (780) 489-3199 voice (780) 487-6397 fax > > Celebrating 19 years of Engineering Innovation (1984 - 2003) > .-. .-. .-. .-. .-. .-. .-. .-. .-. .- > `-' `-' `-' `-' `-' `-' `-' `-' `-' > Do NOT send unsolicited commercial email to this email address. > This message neither grants consent to receive unsolicited > commercial email nor is intended to solicit commercial email. > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu