Audio

Stereo Modifications, 1991 <P>

Stereo Modifications, 1991

This is the tale of how I have improved (IMHO) upon the stereo installation in my 91 S4 since acquiring it some 9 months ago. I didn't want to carve up the interior with aftermarket modifications as I wanted to keep the 'standard' look as much as possible.

An aftermarket stereo had been fitted by the previous owner, so I had SW stereo send me a Blaupunkt Toronto with all the necessary adapters. After repairing and replacing the wiring harness back to the original configuration, installation was a breeze and the sound improved significantly. It also looks better, too.



Blaupunkt Toronto



SW's cable harness doesn't allow for connection of the factory alarm which are the two brown/yellow wires. This is not a problem, but do be sure to wrap the spade connector with insulating tape as it may 'find' something to short out to, causing erratic alarm functionality.

Strangely enough, the Sony ES fitted before was twice as expensive as the Toronto. Goes to show that bigger bucks doesn't necessarily mean better performance.

The 6-channel amp had been bypassed on four of the channels with the woofers still powered by the amp. Sound was improved by rewiring the amp back in. Unfortunately, in bypassing the amp they had severed the plastic terminators. I originally rigged up a temporary connection block which I have now modified permanently with new terminators supplied by SW.

In the Marketing blurb (Porsche literature no less) for the stereo they rate the wattage at 140W. Well 4 of the channels have 20W amps and the 2 woofers have 30W each (no doubt trying in vain to get some bass), but this is with an 18V supply which is a little undesirable. A sticker on the side shows 117W which seems a little more like it.



 


Amplifier in car and a shot with the top removed






Here is the pinout for the DIN connector



Never one to quit fiddling I decided the speakers were up for modification next. The Pioneer GS1040's fit snugly in the door panels and don't require spacers which would have made an uneven look beside the tweeter. Wal-Mart sell these speakers for a very reasonable price. Carving up the standard speaker gave me the necessary bracket to fit the original grill. Tin snips were used to trim the pioneer speaker to ensure everything was hidden behind the grill.



 

Front 4" Speakers



Next up were the rear quarter speakers, I found some Infinity Reference speakers on sale which are a stark contrast to the standard items in terms of build/sound quality (OK so MB Quartz would have been nice but with the standard amp it would have been a waste). Trouble is the standard speakers are very shallow (1.5") and there is not an aftermarket item that will fit in the recess without a spacer. I am in the process of making an aluminum item which will not only increase the depth but also allow direct fitment of the standard grill. I'll post a picture when I have it finished. I am using the Infinity grills as a temporary measure.

While messing around with these rear speakers I was surprised by the lack of volume coming from these 4" speakers (both after market and standard items) especially when compared to the front. I took a look at the crossover fitted to the back of the woofer and found the circuit shown below. This indicated that the speakers were wired 'backwards' with the high pass filter going to the 4" and the low pass going to the tweeter. Swapping the green and yellow wires improved things again. I only have the schematics for the 8-speaker setup so am unable to determine whether this was a factory error.

Shorting out the 6R6 resistor also puts more power to the rear 4" which helps balance the front/rear volume.



Rear Crossover Circuit (factory configuration)



Front Crossover Circuit



Next on the list is the replacement of the 6" speakers.

Hope this helps someone,

Chris Ford

91S4

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