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 Premium Sound - Adding Aux Input
Adding an auxilliary input to your premium sound system

This document describes the installation of a auxilliary input into an EF/EL series falcon fitted with the premium sound. It uses the input for the cd stacker and allows you to plug any mp3 player in using a 3.5mm headphone socket.

WHY?
The release of MP3 compatible head units have made boot mounted CD stackers pretty much obsolete, and many people choose to replace their standard factory stereo with an MP3 compatible CD player. But what if you like the premium head deck and Digital Signal Processor (DSP) that some EL’s are fitted with and would prefer not to replace it?

WHAT?
The answer is an iPod or portable MP3 player. I have a 1GB MP3 player that is slightly larger than a matchbox, plays 10 hours on a single rechargeable AAA battery, and takes only 6 minutes to upload 16 hours of high quality music from my computer.
There are two ways by which an MP3 player can be used through the existing sound system. You could use an FM transmitter which plugs into the headphone port on the MP3 player and transmits the sound on an FM radio frequency, but these in most cases are horrible inventions that crackle, scratch and drift off frequency.
The other option is to add an auxiliary input to the existing stereo system, so that you can plug the MP3 player into the stereo directly. This means no loss of sound quality, and is the option we’ll investigate below.
    Tools required:
  • 1 x Phillips head screwdriver

  • soldering iron & solder

  • thin wire and heat shrink

  • sidecutters

  • wire stripper or a suitable blade, e.g. Stanley knife

  • pliers

  • drill and bits

    Parts Required:
  • 3.5mm switched stereo socket (Jaycar PS-0133 approx $1.00)

  • One 8 pin DIN plug male

  • One 8 pin DIN plug female

  • 3.5mm stereo cable



HOW?
The easiest way to add an additional input is to patch into the existing audio cables from the CD stacker. This can be done either in the boot or behind the DSP, or at any point along the wires connecting the two; it just depends where you want your auxiliary input to be placed. In my case, I wanted the MP3 player to plug into the dash next to the head unit, and therefore had to work out which wires leading into the DSP were the audio signals (left channel, right channel and signal ground) from the stacker

In order to identify the audio signal wires leading into the DSP, I pulled apart the in-boot CD stacker and was able to establish the pin out from the CD stacker. This is shown below for those who want to cut into the wires at this point and have their auxiliary input located in the boot.


Premium Sound System (1996 EL Fairmont Ghia, series 1) - CD Changer Pinout



I then chased the wires to the front of the car, behind the DSP, and the pin layout for the plug that inserts into the DSP is shown below.

Premium Sound System (1996 EL Fairmont Ghia, series 1) - Digital Signal Processor



For the EF series the cd stacker has a round plug and not a square one. Below is an image of a round 8 pin DIN plug and each pins function.

Premium Sound System (1995 EF Fairmont Ghia) - CD Changer Pinout
EF Alpine CD Changer PIN Functions
Pin No Function
8 Ground
6 +12v
7 Accessory Switch
1 Communications Bus Data
3 Communications Bus Ground
4 Audio Signal Right Channel
2 Audio Signal Ground
5 Audio Signal Left Channel
Shell Chassis Ground


To connect the auxiliary input, you need to cut into the existing Left Channel, Right Channel and Signal Ground wires, and join in a new stereo input plug. The standard wiring for a 2.5mm / 3.5mm stereo plug is as shown below, and this can be used to work out your connections to the auxiliary input socket.



Either an open socket or a switched socket can be used, but they are slightly different in the way they work as explained below. A switched socket is without doubt the more elegant solution.

Switched Socket:

A switched socket actually switches inputs when an audio plug is inserted into the socket. Thus when no plug is in the socket, the CD stacker line in is connected to the DSP, and the auxiliary input is disconnected. When a plug is then inserted, the CD stacker line in is disconnected and the auxiliary input is connected. This means that you only ever have one set of audio signals going to the DSP at a time, and therefore you will never hear the auxiliary input overlaid on the CD stacker output.

An example of a 3.5mm switched stereo socket is Jaycar PS-0133 ($1.00).

Open Socket:

If you use an open socket connector, both the CD stacker and the auxiliary input will be connected at the same time. Thus if you have a CD playing and your MP3 player connected to the auxiliary input, then you will hear both tracks playing at once, overlaid on each other. An interesting effect.

Originally I had hoped that the pause function on the CD player (hit the CD button while one is playing to pause / play) would simply "pause" the CD, allowing the MP3 player to be heard on its own. Unfortunately the pause function also mutes the stereo, so that the MP3 player cannot be heard either!

The solution is to use your computer to burn a CD which has a single, completely silent track. I used Nero Wave Editor (NWE) to record 30 seconds of sound while I had my computer’s microphone unplugged, which gave me a silent track. I then used NWE to copy and paste this 30 second audio clip a number of times until I had a 70 minute blank audio file. I then saved this as a .wav and used Windows Media Player to burn it to CD.

I have this CD permanently located in the Disc 1 position in my stacker, and whenever I want to use the MP3 player I simply set the stacker on Disc 1. The sound coming from the stacker and the MP3 player are still overlaid, only the sound coming from the stacker is silence.

The socket I used is a 3.5mm open stereo chassis socket, Jaycar PS-0132 ($1.60)

How the socket works:



You will now need to solder up your "MP3 adaptor" to plug inline with the existing CD Changer - DSP Bus. Using the wiring diagram below (if using a switched socket) put the piece together. I would suggest making the item with the male and female 8 pin DIN plugs so if you ever want to remove it and put the stereo system back to stock, it is simply a case of removing it.



Installing the socket:


I installed the Jaycar PS-0132 socket just below the cigarette lighter socket and slightly to the left, as shown in the photo below. This socket requires a 6mm diameter hole, but make sure that you start off with a smaller drill bit (say 3mm), then slightly larger (say 4.5mm), and then either a 5mm or 5.5mm before using the 6mm drill bit. The 3mm drill bit allows you to accurately position the pilot hole, and then increasing in size in a couple of steps avoids tearing around the edges of the hole, resulting in a neat finish. Also, make sure that you do not use too many revs on the drill or the drill bit will heat up, melting the plastic nicely. Use a large bit now by HAND!!! and clean up the edges gently.

The plastic surround is a little too thick for this stereo socket to protrude properly so you will need to slightly taper the front of the hole so the socket nut will sit flush. Be very carefull here so you don't damage the front facia or tape too deep. You only need about a 1mm indent on the front for the locking nut to fit.

Note that the socket must protrude sufficiently for the plug to go all the way into the socket, or you will have contacts breaching across the insulators on the plug and may end up with only one channel working, no channels working or other weird effect.



Using the new auxilliary plug:

Obtain a stereo cable that has the required plug to fit your MP3 player on one end (either 2.5mm or 3.5mm), and the correct plug to fit your auxiliary input socket on the other end (I recommend you use a 3.5mm socket as they are much sturdier).

Plug one end into your MP3 player and the other into your new auxiliary input socket. Press “CD” on the car stereo. If you’ve used a switched socket, you’re up and away! If you’ve used an open socket, select “Disc 1” on the stacker, and set the player to “Repeat Disc”.

Then press play on your MP3 player, and digital tunes will start cranking!

The EF/EL use an Alpine stacker and amp. The significant thing about this is that it uses the Alpine bus system to communicate with the stacker, and the moment that the stacker is powered down, the DSP brings up a "CD Err" msg or similar. So there's no way around it but to have the stacker up and running, and then just cut in your own audio feed. I was initially hoping that the CD pause function would do the job as this would have been really neat, but Alpine have done too thorough a design with their head unit

If you use the switched stereo socket, then there is no dodgy CD required. The switched stereo socket does all the switching required. When you plug in your MP3 player, the sound from the CD stacker will automatically be cut and the MP3 player will be fed through to the stereo, although admittedly the display will continue to show the CD playing.

The stacker outputs at a set volume level, whereas your MP3 player headphone jack is variable level. I set my MP3 player at full volume, and this gives similar volume to the stacker.

For example, if you had a test CD that played one note at a constant volume, and tried playing it via the stacker and then from your MP3 player, the stacker would output a set 'reference' voltage that corresponded to that volume, and the deck would then amplify it. If this reference voltage was (say) 4V, but then your MP3 player outputs the same note at 3V, then the MP3 player would be noticeably quieter. On my MP3 player I am able to use the volume control to get the MP3 player output voltage very similar to the stacker 'reference' voltage, but this is MP3 player dependant.

I have noticed that when listening to CDs via the stacker but with the MP3 player plugged in and switched off, the CD volume is very quiet. This is something to do with the way that the new auxiliary in changes the impedence of the line in from the stacker. Changing to a switched socket would certainly fix it, or you can just unplug the stereo lead from the auxiliary socket.
 
 Document Summary
 
Document description: How to add an auxilliary input to your premium sound system
Document written by: Moph on 26 2006>, Copyright © 2006 Moph, all rights reserved.
Document revised: 03 2006 - Revision 1.1
Document views: 14606 since 26 2006



 

 

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