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A Bundle of Myrrh

"My beloved is unto me as a bundle of myrrh." Song of Solomon 1:13

Auxillary Input for Car Stereo

November 4th, 2011 by Phil

While adding an AUX input does not sound fun, it is quite practical.  Hopefully this overview will inspire you to do the same.

CD’s have gone the way of the record, 8 track, and cassette tape (or at least they have started down that road).  They hold so little music and suffer from small scratches, causing harsh digital noise.

For the future of music and a practical electronic hack read the rest of this post.

Portable Mp3 players are now mainstream.  For under $30 they hold up to a 1000 songs and can run for hours.  I am not talking about the over-priced, faddish Ipod/Inano/I-whatever, but generic mp3 players.

Our new van (1998 Ford E350) does have AM/FM and a tape player.  It is not very useful to have a tape player.  Reading some research, I decided to hack the Van’s stereo and add an AUX (for Auxiliary) input.  Not only would it be useful for an mp3 player, but any device that drives headphones.  For example, a portable DVD player can be hooked into an AUX input and sound would come through the car speakers.  Of course, a DVD player could play old-school CDs, like any newer car.

Much like cheap headphone cassette tape adapters, I am sending the mp3 player output (Aubri’s old Ipod) to the tape input.  But I am bypassing the magnetic receiver, and the noisy motor assembly.

After taking out the stereo and the tape deck, I found printed on a small circuit board of the tape deck: FL FR RR RL and GND.  I disconnected these wires from the tape player and hooked into them.  I discovered that RL was the left channel and FR was the right.  I tied RL RR  (commons) and GND together.  This works, however the sound was muddled and of poor quality.  I figured out that the normal tape output signals were weaker than the headphone output.  So I wired 100 Ohm resistors in series with the left and right channel inputs.  Here is a trial:

Though the picture has a resistor in series with the commons of the L and R channels, I did not stick with that configuration.

This is the almost finished product.  After tapping into the correct wires and soldering the wires to the 1/8″ headphone cable in place I secured the headphone input wire with a holder, so it would not pull on the connections.

Two neat modifications I made: First, I disconnected the motor for the tape deck.  Not only it is annoying, but I am sure it would introduce noise.  Second, there was a pressure switch which told the stereo there is a tape in the player.  I soldered those wires together at the switch, so when the tape input is selected, the stereo always thinks there is a tape in there and therefore will play the music through the headphone jack.

It works pretty well. It is not CD-quality, but I would say it’s about FM quality, which is plenty good enough for a big, noisy van.  If I had been more patient, I would have tried higher valued resisters to further limit the signals going into the tape inputs.

Coming soon: Aux input for a Toyota Camry

One Response to “Auxillary Input for Car Stereo”

  1. grandmere says:

    Well I don’t know what this says; I’ll leave it to Butch to interpret! :-)