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Auxiliary Audio Input Jack for Older Radios

September 23, 2010 | Troubleshooting & Repair

By Russ Collins

 

Here's a schematic for an MP3/Satellite/iPod/iPhone audio input jack for older radios. I use it to play an iPhone through a Blaupunkt in a 1959 Porsche. It's not stereo; but it sounds ok, is loud enough, and maintains the radio's originality. It involves adding a miniature phone jack to the side of the radio and performing some minor re-wiring inside the radio. Plugging in any external audio switches the radio from internal audio to the external source.

Parts are around $5 from Radio Shack:

  1. One 1/8" Stereo Phone Jack, part number 274-0246
  2. Two 0.1 Microfarad (MFd), 50 Volt ceramic disk capacitors, part # 272-0135 (package of two).
  3. Two 100 Ohm, 1/8 Watt carbon film resistors, part number 271-0005 (package of 5).

With the radio in the car, determine a suitable location for the jack. Be sure the dashboard support doesn't get in the way. This photo shows a typical location.

A more important consideration is the space inside the radio. This photo shows the inner view of the above jack and the parts layout. In the photo, the lower red wire comes from an existing .01 MFd capacitor in the radio and the upper red wire goes out to the radio's volume control. This is shown in more detail on the next page. I used regular stranded hookup wire.

The next photo shows the location of the tap point in the Blaupunkt near the volume control on the lower right. The two red wires from the jack in the previous photo are snaked through the radio to a point near the volume control.

See the following enlargement. The connections are a little difficult to see, but the .01 microfarad capacitor on the left (marked "0.01 uF") is originally attached to the radio's volume control terminal furthest to the left. Unsolder this lead and solder the red wire that runs to the new jack to it. Then solder the red wire that comes from the resistors on the new jack back to the terminal of the volume control vacated by the removal of the .01 capacitor. That's it. No guarantees but this worked for me. Hope it works for you.

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