Replacement head unit question for car with Bose

[porscot]

[FONT=calibri"]The question is ‘has anyone replaced the PCM head unit, kept the Bose amp with all speakers working’ however if you wish the longer version please read on.
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[FONT=calibri"]My 2003 996 C4S has a Pioneer AVIC-F920BT head unit.[FONT=calibri"] [FONT=calibri"]It has taken around 6 months since getting the car for me to realise that only the front dash speakers are working and nothing is coming out of any of the Bose speakers.[FONT=calibri"] [FONT=calibri"]The car would originally have had a PCM head unit.

[FONT=calibri"]I did a little research and there seemed to be a lot of old posts on the internet about the incompatibility of the Bose amp with aftermarket head units so I thought I would take the car to my local car audio specialist to ask for their advice.[FONT=calibri"] [FONT=calibri"]They offered to look at the car for no charge to work out what needed done.

[FONT=calibri"]After a little over half an hour I asked for an update (not wanting to overstay my welcome for a free review and thinking that pulling out a head unit to check if all wires were connected would not take that long for a specialist). [FONT=calibri"] [FONT=calibri"]As the car was in their workshop I did not see exactly what was done but got told that at this time of year they have to be careful removing panels due to the cold, not wanting to break fittings and they were just putting it back together.[FONT=calibri"] [FONT=calibri"]Their advice to me was that whoever had replaced the head unit must have also replaced the front speakers and wired them directly to the unit bypassing the amp and that if I wished all the speakers to be working I should look to buy another Bose amp and 2 speakers for the dash.[FONT=calibri"] [FONT=calibri"]If I supplied them they would then be able to get it all working.

[FONT=calibri"]I had some doubts about what I was being told. A couple of minutes of searching on the internet to identify where the amp is located in car, I realised that I had seen it before as it is in the ‘frunk’ on the passenger side under the carpet next to the spare wheel.[FONT=calibri"] [FONT=calibri"]It took another couple of minutes to take off the two screws that held in one of the speakers to see that it was an original speaker.[FONT=calibri"] [FONT=calibri"]I thought it not worth bothering to check the one of the other side.[FONT=calibri"] [FONT=calibri"]The surround for the head unit pops off easily and although they are not really required, a Pioneer key either side of it makes it easy to remove to check what is behind to see whether it was clear some speakers were connected and others were not.[FONT=calibri"] [FONT=calibri"]There are a couple of spare wires but nothing to suggest the fitter of the head unit had done anything other than try to connect all speakers.

[FONT=calibri"]So, concluding that if the shop did take some panels off I have no idea what ones they removed or why they bothered.[FONT=calibri"] [FONT=calibri"]They could not have removed the speakers as if they had they would have known they had not changed and that the wiring to them looked original Porsche.
[FONT=calibri"]I therefore thought I would investigate a bit further to see if I could get it working myself.[FONT=calibri"] [FONT=calibri"]I found some posts that suggest an additional harness is required.[FONT=calibri"] [FONT=calibri"]They all seem relatively recent so I assume that when anyone first wanted to replace the Porsche head units there was no adaptor but as the adaptors seem to be getting sold for many Audi models as well it must now be worth making an adaptor.[FONT=calibri"] [FONT=calibri"]Some posts suggest Autoleads PC9-408 e.g. http://www.ebay.co.uk/itm...ame=STRK%3AMEBIDX%3AIT but others suggest is can cause a thump on start up so to use Connects2 [FONT=calibri"] [FONT=calibri"]CT51-AU01 e.g. http://www.ebay.co.uk/itm...D8skhqKs3jAvncjRgDCumg[FONT=calibri"]
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[FONT=calibri"]Before buying the adaptor I am looking at pictures of the CR51-AU01 and noting as well as the little black box there seems to be 3 adaptors plus what I assume to be a blue power lead.[FONT=calibri"] [FONT=calibri"]I thought if this was required it would sit in the existing wiring so only needing 2 connectors, 1 in, 1 out plus potentially the power lead.[FONT=calibri"] [FONT=calibri"]Has anyone fitted one of these?[FONT=calibri"] [FONT=calibri"]Do they work?[FONT=calibri"] [FONT=calibri"]If I get one it is necessary to disconnect the battery first to fit?
[FONT=calibri"]I appreciate there are many other options including ditching the Bose amp however as it has taken me as long to notice I was missing the other speakers it is not worth more than the path of least resistance to see if I can get them working.[FONT=calibri"] [FONT=calibri"]Any input appreciated.

[FONT=calibri"]Thanks and Regards
[FONT=calibri"]Graeme

 

[Richard_Hamilton]

Neither of those leads on eBay are right for a 2003 Bose system. Bose uses fibre optic cables from the PCM (or CDR23) to the amplifier to transmit sound and control signals. If you want to retain the Bose amp, you need an RCA to Fibre Optic interface. Connects2 make one for the 997, but it doesn't say if it works for the 996 on their web site. http://www.connects2.co.uk/Product/ProductItem/CT51-PO04

The original installer must have disconnected the dash speakers from the amp, and wired them direct to the new head unit.

If you can live without the subwoofer, you can buy an Autoleads cable which bypasses the amp - connecting the speaker outputs from the head unit directly to the speakers: http://www.ebay.co.uk/itm/Autoleads-PC2-95-4-Car-Audio-Harness-Adaptor-Lead-Porsche-/191792524040

The snag is that the speaker impedances on Bose systems are (iirc) 2 ohms, rather than 4 ohms on standard car stereo speakers.

The only other RCA-to-fibre interface I know of is the NAV-TV HUR, but it is very expensive. Hence why most people replace amp and speakers when doing an audio upgrade.....

 

[Pieman7]

I changed mine I didn't have Bose but it was run with fibre optic like Richard says the connects adapter worked but I need to change the amp because all speakers work at the same time there's no fade from front to back.

 

[porscot]

Richard, thanks for the detailed reply. The CT51-PO04 is around £155 with the NAV-TV around £280 (https://www.nav.tv/products/porsche-pcm2-21-head-unit-replacement-por-hur) That link states PCM2/2.1 compatibility and as I understand it the version that would have been in my car was PCM2 so potentially compatible. I'll make a couple of calls tomorrow to see if I can get a definitive answer from either. If the price was in the range of the items in my original post (£20-30) it could be worth a punt but at these prices definitely worth getting a straight answer before purchasing.

Regards

 

[porscot]

Took my car back to the audio fitters today who looked at again in more detail and found the end of the amp cable. They had assumed before that all 996s had the amp in the same place. When I pointed out where it was they noticed someone had already bypassed the amp but only connected the front speakers. It looked more trouble than it was worth to undo the job that had been done and install a fix that got all speakers working through the amp so they wired in the door and rear panel speakers directly leaving the speakers behind the rear seats unconnected.
While they had things apart they fitted a replacement cup holder that I had bought as someone had broken the front off. Their workaround had been to use double sided tape but that was only suitable when the cupholder is closed and never opened. Not that it is so noticeable on a working unit but the front moves on a cog when the cup-holder opens so it clears the fascia to the side.
Lesson for myself for next time I buy a second hand car is to check everything works. If nothing else it would strengthen negotiations.
At least now speakers and cupholder are now working.

Regards