Thought I'd share my latest exploits in trying to get a decent audio output from my AS-2 system.
ok, lets start with the problem. I've got a stock AS-2 setup in my 2004 9-5. The main problem is that it's missing a big chunk of the audio range low/mid frequency, then has pretty crappy base response unless cranked right up. I've been trying to sort this out the hard way, which I can't recommend:
1. Replaced the dash speakers with a pair of decent Pioneer units (TS-876).
> Sound quality certainly improves, but still missing the low/mid-range.
2. Replaced the door speakers with a pair of 4ohm JL Audio coaxials, 94dBm sensitivity
> Volume substantially reduced (confirming these are directly driven from an amp circuit, not a crossover as I was hoping)
> Speakers are still only kicking out very low frequency, no mid-range.
3. It seems most of the audio problems are all coming back to the amp, so I pulled it out to play with (what a bitch that was).
Firstly, I need to contradict Angry Kitchen: head unit to amp connection is NOT pro-audio differential line level, it's bog-standard speaker outputs (which are almost all differential in cars). This means replacing the head unit DOES NOT need any special circuitry to work with the amp. Just connect the speaker outputs into the amp (which is exactly the current wiring config on the DIN connector - no change needed).
The amp itself is a pretty archaic design. The service manual dates it back to 1996 for the Saab 9000, but the circuitry looks much older than that (lots of through-hole, hand soldering and big 1206 SMDs). I've attached an extract of the service manual (full version too big to upload). The amp has got both low-pass and high-pass filters installed to decouple the front speakers. The door speakers have a lowpass cutoff at 140Hz, whereas the dash have highpass at 125Hz. I get the feeling Saab invested all the cash with Harmon Kardon here, leaving peanuts to 'throw something together' to fit. Theres no way 3" dash speakers are going to be able to pick up the entire range from 125Hz upwards, so no change of door speakers is going to make the slightest difference...
This is now where I'm up to. It pretty much leaves the following options for sorting out the audio:
1. Buy a new head unit, disconnect the amp in favour of some passive cross-overs (plus some minor rewiring)
> A decent head unit can take over the work of the amp, just loosing centre speaker.
2. Tweak the amp circuit to change the cross-over frequency
> circuitry is all pretty simple and accessible, just need to find the right caps to change.
> this also gives an opportunity to change the fixed gain on the door speakers, allowing 4ohm units to work properly.
3. Find a new amp
> not sure anything exists to do this job directly
> going to involve lots of rewiring as theres no way I can mount one in the current location
Will keep you updated as this progresses, thoughts/comments welcome.