Audi S4 Stereo Swap - Subwoofer Issues???

Lion Heart

Lion Heart

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Hi guys

Need some help!!!

I just bought a new double din aftermarket head unit compelte with DVD player, Nav, Bluetooth etc to replace the Symphony II unit in my Audi S4 (2003 B6)...

However, I've heard on the grapevine that I may have issue with the centre speaker and subwoofer???

I've checked the wiring. On the new head unit it is outputting four channels (L and R front and rear sets). But on the car (Audi) side of the plug it is only taking a singal for the front speakers, so the rear are not intended to be drawn from the original Symphony II unit...

I've heard that there's a seperate amp in the rear that drives the centre (rear???) speakers and also the subwoofer.

If this is the case, from where does it get it's signal? I assume the signal must be sent from the Symphony II head unit???

So if I change head units am I likely to lose the centre (rear?) speakers and subwoofers? If so - that sucks big time!

PLEASE HELP!!!

Many thanks

Lion Heart
 
Thanks for that. Very interesting stuff!

I'll have to sit down and take this all in as some reading there.

By the way - did your radio booster give you as good a signal as the original head unit did?

Many thanks!

Lion Heart
 
Hi again

I just looked over the plugs and connectors with the new head unit, and it has two cables with female photo (RCA) plugs on the edn labelled "2 Zone L Out" and "2 Zone R Out" respectively...

I assume that this might be the feed for the rears???

I have not looked at the rear amp side of things yet - what connectors are on the amp? And is there an easy place I can access the rear speaker wiring to save running the wires right the way into the rear?

Also, stupid question - where is the rear amp on an Avant?

Many thank!

Lion Heart
 
The amp is mounted on the sub behind the drivers side boot panel.
You can pick up the feed to the rear speakers from the connector on the amp, but you still have to run the cables back to the HU from the amp, no way round that I'm afraid.
B6rear-subpinout.jpg


To feed the RCA's from the HU to the amp you just need a PC9-404 wiring adapter, this will also feed the rears if you are not rewiring them. Rewiring the rears does also mean the sub will be totally not loud enough. Better off leaving them running off the stock amp and fading to rear to balance the sound.
 
Hi Guys

Thanks for the help!

Got into it yesterday and is now all set up. Strange thing is - after going around the houses it was a LOT easier than expected...

I have a 2003 B6 S4 Avant and is has the standard (non-Bose) speakers. The head unit was Symphony II, and I've replaced it with an all-singing head unit...

The new head unit outputs amplification for front L&R as well as rear L&R, but the plug in the car only picks up the front L&R and the rear have no pins in.

So, posted this and found what I thought the best solution:

The hew head unit also has phono outputs for Zone 2 L and Zone 2 R, which it seems are for sending the stereo signal (non amplified) to the rear...

So, wired it in completely taking the signal from those phono's to the rear amp. Tested it - nothing!

Noted that the rear amp did not seem to be powering up and the power in cable (white as I recall?) was not giving the amp a switching live. So, found that same wire in the front using a multi-meter and put it into a switching live... Rear amp came to life.

BUT - and this is the big but and weirdest of all, the rear speakers only operated on one volume and would not go up and own in volume when turning the volume knob (whereas the fronts did of course). BUT the subwoofer DID go up and down with the volume control (fed from the rear amp as well it appears - hence I found that odd!)

I assumed that this must be because the rear amp does not control volume and is only being fed with the pure signal via the phono outputs on the head unit. So the front controls the volume, and the rear just amplifies what it is sent.

So, two options on how to go forward:

1) Take the amplified rear signal from the head unit straight into rear speakers by cutting the cables that go into the plugs for rear L&R on the rear amp and joining those cables to the amplified signal from the front, so the head unit is directly dirving the rear speakers, and ALSO leave the set up I had already done with the phono outputs to allow the sub to work correctly

-or-

2) Reconnect the rear amp to EXACTLY how it was before I attached the new cable, but now it definitely has a correct switching live to actually power the rear amp.

Now, number 2 should not work in theory based upon what people have said on here. But, as by the far the easiest option (and also quick to do) I tried it and it only ****** works perfectly!

So, basically I could have done this by not touching ANY wiring ANYWHERE except for the switching live feed to the rear. Worth trying that first if you get a similar issue as it's a LOT easier than the alternatives!!!

Yes, you need to set the fader slightly to the rear to balance out between 45W driving the fronts and 20W driving the rears - but once that's done it's spot on and sounds perfect!

So, maybe some people have gone around the houses on this which is why I thought I'd post this here as there does appear to be a very easy solution in this instance.

Hope this is helpful???

Lion Heart
 
As said all you needed "To feed the RCA's from the HU to the amp you just need a PC9-404 wiring adapter"
 
How does the adapter get the switching live feed?

You don't need to run the RCA's from the front at all. I tried that first of all and then wired it back to it's original form.

Literally all that was needed to make it work was to get the switching live (white) cable connected so the amp has power, and it worked perfectly.

Lion Heart
 
The adapter gets the switching feed from the new HU's power antenna or "remote on" feed and feeds this to the correct pin on the Audi loom which feeds it to the amp just like the stock HU.
 
Ah ok - I thought the adapter went on the other end (rear amp). So yes - that works too!

But just to confirm - don't believe all the threads saying you need to run cables from the front to the rear to get the rear amp operational - as it will not always be the case (as it wasn't for me) so try the easy way before the hard - may save some time and headaches.

Just trying to be helpful. Wish I'd known as would have saved me a couple of hours faff.

Lion Heart
 
i ran new speaker wires from my kenwood headunit to the rear amp plug like andy suggested, works spot on, plus after installing extra rear subs the standard sub has been removed completely, due to the rear subs running on a seperate amp
 
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