DIY: Add Aux Input to Symphony Head Unit
This is my first post here. I recently purchased a B5 A4 2.8L 30v quattro. I wanted to add an aux input to the stock head unit. I figured that I would document the process so someone else could do it too.
Here is a link to the Google Doc (with pictures):
Audi Symphony Line In Through Tape
Here are instructions (although they are not formatted as nicely as the Google Doc and I cannot upload all of the images):
First off, the original idea goes to TheLaughingMan on vwvortex.com (see the post here). I followed his instructions to add an aux input to a double-DIN Monsoon head unit in my Golf.
Recently I purchased a B5 Audi A4. I like the idea of having a decent system but keeping the stock look. As such I wanted to keep the factory head unit--which does not have an aux input. Others have added an input to the CD changer, but I have attempted that before and did not like the results. There were three main reasons I wanted to add the input to the tape circuitry rather than the CD changer:
I had done the tape input before and was familiar with it.
I will likely never use a tape again, but there is some chance that I would use a CD changer.
When I attempted adding an input to the CD changer the signal was much lower than I wanted. Granted, this was on a different vehicle (an Acura), but I was not certain it would be different.
Be advised: any tampering you do with your radio will void your warranty and possibly break your head unit or something else. DO THIS AT YOUR OWN RISK.
Note that this modification involves some minimal soldering.
Tools & supplies needed (example links included on some items):
VAG head unit removal tools
#1 Phillips screwdriver
#2 Phillips screwdriver
Soldering iron
Solder
Cassette-to-⅛” TRS adapter
⅛” TRS jack
Drill
Drill bit set (one needed for the ⅛” TRS jack)
Blue Loctite (optional but suggested)
Hot glue gun (optional but suggested)
Hot glue (optional but suggested)
Instructions for Audi Symphony head unit:
1) MAKE SURE YOU KNOW YOUR RADIO CODE BEFORE UNPLUGGING THE HEAD UNIT.
2) Remove the head unit using appropriate head unit removal keys. Do not try to pry it out without them. You need at least two; they can be purchased from many places online (Crutchfield, Amazon, etc.). The four slots are shown below in Figure 1.
Figure 1: Location of Slots for Head Unit Removal
3) Unplug the electrical connectors from the back of the head unit. Take note of the location and order of each (although they will only fit in one slot).
4) Take the head unit to a well-lit work area.
5) Remove the four screws on the sides of the head unit that hold in the faceplate. They are on the sides. See Figure 2.
Figure 2: Location of Faceplate Screw and Aux Cable Routing
6) Carefully unclip and remove the faceplate.
7) Remove the four screws that hold the bottom plate; remove the bottom plate.
8) Remove the four screws that hold the top plate; remove the top plate.
9) Remove the four screws that hold the left plate.
Note that all of the shorter screws go into the sides of the head unit; the longer screws go through the back plate.
10) Carefully remove the ribbon connector shown in Figure 3 and push it back into the unit. This prevents audio signal from getting to the preamp (thus preventing any tape hiss) but renders the tape deck non-functional. It is, however, entirely reversible.
Figure 3: Ribbon Cable from Tape Head to Preamp
11) If you care to see how I determined where to connect the aux input, check out the datasheet for the Sony CXA2510AQ. As the datasheet was difficult to track down, the pinout of the chip is below in Figure 4. The pins labeled “LINEOUT1” & “LINEOUT2” are the outputs from this pre-amplifier. It is important to use the outputs from the chip, as it bypasses its equalization (which was designed for tapes).
Figure 4: Pinout for Tape Preamp Chip (Sony CXA2510AQ)
12) Turn the unit over so that you are looking at the bottom and locate three test points (large solder spots): “TP271”, “TP371”, and “GND”. “TP271” is the left channel and “TP371” is the right. See Figure 5.
Figure 5: Main Board Signal Test Points (Green = Ground, Red = Right, Blue = Left)
13) Cut the entire cord off of the tape adapter at the tape. Keep the tape.
14) Carefully strip the wire from one end of the tape adapter.
I found it easiest to add a bit of solder to each test point before attaching the wire. This just makes it easier to solder the wires.
15) Solder the red wire (right channel) to “TP271”.
16) Solder the blue wire (left channel) to “TP371”.
Note that some tape adapters may not have color-coded wires (or the colors may be different). As mentioned above, this is fairly easy to switch later, so do not worry about left-vs-right too much.
17) Solder the ground wire to “GND”.
Note that this one is important. Do not get it mixed with the signal wires.
Note also that there may be two ground wires in your cable. If so, I suggest twisting them both together and soldering the pair.
18) Optional but suggested: use hot glue to glue the wires to the bottom of the circuit board so they are not easily disturbed. Be careful of the metal standoffs on the bottom plate: they should not pinch the cable. I suggest doing a test-fit before gluing.
19) Re-install the CD player and side plates (if they were removed).
20) Cut off the ⅛” TRS plug at the end of the tape adapter cord. Thread the tape adapter cord through the hole on the right side of the head unit (see Figure 2). Make sure you do not put the cord through the lock slot as whoever removes the head unit next would likely cut it with a removal tool.
21) Carefully drill a hole of the appropriate size at the approximate location shown in Figure 1. Make sure you check the fitment and dimensions multiple times before drilling. There are cavities on both the left and right of the head unit that have space for the jack. Note: I am intentionally not including dimensions I used, as your jack may be different than mine.
22) Carefully break the corner off of the faceplate circuit board as shown below in Figure 6. This provides a space for routing the cord.
Figure 6: Remove Tab from Circuit Board as Shown
23) Reassemble the remainder of head unit (top plate, bottom plate, and faceplate).
24) Install your ⅛” TRS jack. I suggest using some Loctite on the nut to prevent it from loosening.
25) Measure the cable that you have soldered to ensure that you have enough to reach your jack before cutting it. To make it easy I suggest adding about 1.5” more than you think you will need.
26) Strip the cable and attach the wires to the appropriate spots on your jack. If you purchased the same jack as me you will not have to solder anything at this point and can easily switch the right and left channels if need be.
Note: R = ring/right; T = tip/left; S = sleeve/ground
27) Plug the head unit connectors back in.
28) Carefully slide the head unit back into the car, paying close attention to the jack and cord you just added.
29) Power the head unit back up, enter the code (if required), put the tape into the tape deck, plug in an audio source of your choice, and enjoy your new aux input!
Note: I had to remove part of the tape adapter internals in order to get the head unit to stop switching sides. It was easy, but unexpected, as I did not have to do this with the Monsoon head unit I modified. See Figure 7.
Figure 7: Tape Adapter Modification--Only these Three Gears Are Needed
30) Final note: someday I may come back and figure out how to fool the head unit into thinking there is a tape inserted when nothing is there. However, this is a bit of a daunting task as there are a number of microswitches and some logic circuits involved and I have not yet taken the time to figure out exactly what is going on. Pressing a switch is not enough: the tape deck knows if both spindles are turning and will stop if they are not. If someone has a spare head unit they would like to donate to the cause it would make this much easier. The head unit could even be mostly broken as long as the tape portion and the main board are functional (I would be able to do some testing on a unit with bad outputs and/or a broken CD player).
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Originally Posted by Wooshy
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