I replaced the Gamma Bose cassette head unit in my parent's 1995 Audi A6 with a Blaupunkt CD head unit. I adapted the harness to feed the pre-outs on the Blau to the Bose amps. It works and sounds great -- EXCEPT -- that the amps/speakers make an annoying loud popping sound whenever you turn on the system, change a source, change a radio station, etc. I also tried a Kenwood head unit with a different pre-out voltage -- same popping sound problem.

Any idea what gives? A tech at Best Buy suggested feeding the speaker outputs directly into the Bose amps rather than the pre-outs, but that did not make sense to me. Would a speaker level to pre-out line level converter help?

If so, I would bypass the Bose amp and go direct to the speakers.

Feeding the speaker outputs to the Bose amp is not a good idea. And using a hi-lo adapter is redundant, as you have already fed the Bose amp a clean pre-amp signal.

<ul><li><a href="http://www.audiworld.com/tech/elec.html">FIX</a></li></ul>

You can buy the speaker input adapter which does both. This gets rid of the popping but will give you a substandard signal, as it's already been amplified very well by the Alpine, then amplified again badly by the Bose amp.
Don't whatever you do by pass the Bose amp as the ose speakers are 2ohm impedance which could/will knacker the Alpine.
The only good way to sort it is to add some capacitors across the RCA's which will filter the pop, but this is a right pain to do.
You could also try a ground loop isolator on the RCA's. Basically the Bose amp uses a bizarre capacitor array on the front stage to the amp. This doesn't like the industry standard method for silencing the RCA's when you do anything electrically noisy like change CD track etc. So when an aftermarket HU grounds the RCA's on these occasions (so you don't hear any electrical clicking) it discharges the capacitors which causes the pop.

Thanks, MacSub for the thorough reply. I'd just as soon keep the Bose amp and speakers. Can you give me some more detail as to how to add the capacitors across the RCA pre outs? What value capacitors, connected between which leads? if that doesn't work, I'll try the hi-lo converter. I recognize the drawbacks, but my parents aren't audiophiles, they just don't want the annoying popping sound.

... using a line-level converter to feed the speaker-level outputs from the head unit into the Bose amp (through the stock radio input plug) was my resolution when <a href="http://forums.audiworld.com/audio/msgs/60037.phtml">replacing the Delta head in my '97</a>. I tried ground loop isolators on the RCA's and it didn't do a thing to stop the bass thump.

<ul><li><a href="http://www.audi-sport.net/vb/showthread.php?t=26307">http://www.audi-sport.net/vb/showthread.php?t=26307</a</li></ul>

Many thanks for the link to the instructions. I'll give it a try and post to let all know if I had the same success.

..while it is not the electricaly sound or recommended way, it can be done without "knackering" the Alpine.

There are ~12 Audi/Bose cars out there for years now without failure with aftermarket head unit connected to Bose speakers.

Some the Bose amp crapped out, some the car owner didn't want to spend/ have the extra money to replace the speakers.

I imagine it would sound bloody awful as well, but that's another debate.....

The instructions you pointed me to involving placing a non-polarized 15 mF capacitor in line with the pre-amp outputs of the Blau headunit worked like a charm! No more popping noise and avoided expense and hassle of replacing Bose amp and speakers.

For others intersted, I could not locate 15 mF capacitor so I ended up using a non-polarized 10 mF and 4.7 mF capacitor, wired in parallel, on each channel.