Audi S4 Stereo Swap - Subwoofer Issues???

[Lion Heart]

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

[SamCh]

i found this issue when changing mine. it has a built in amp which powers the back speakers. Gave it to halfords in the end and they fitted it for me for 40 quid.Dont know if they'l charge more for satnav unit.

[Lion Heart]

What did Halford's actually do? If those guys can do it then I'n sure it can't be that complex?

Any ideas very welcome!!!

Lion Heart

[technohippy]

your aftermarket unit will most likely have low level outputs designed to be used with an aftermarket amp setup, you could wire those into the rear channel so that the audi amp is being fed a low level signal like it wants, however i think the k bus turns on the amp for the rear so you might struggle to power them on.
also alot of people have trouble even powering on an aftermarket head unit as there is no ignition 12v feed on the b6 as it also uses k bus, i had to run a 12v feed from my fusebox into the back of my stereo to get it to boot on startup

[Lion Heart]

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 bloody 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

[technohippy]

that is pretty handy to know actually, good work.
i currently have no rear speakers anyway as i find the sound stage better with just my fronts and sub, also as i pointed out to my passengers i dont sit in the back much haha..

[Lion Heart]

Hi there

Many thanks - thought it worth sharing as it may save some people a lot of time fiddling needlessly.

I know what you mean about the rears, but it really does sound more 'full' having all of the speaks around the car outputting rather than just the fronts.

Also of note, some people of forums mentioned a requirement to disconnect the front centre speaker because it's extremely high pitched. I didn't, and sounds spot on with it connected as standard.

Glad to be of some help!

Lion Heart