More wrong info from a hi-fi shop. (archive)

Ok. Since I've been involved in the design of more than a few car amps in my carreer, I'll simply say that IMHO you have been fed misinformation. It was probably unintentional, most shops just don't know about the technology within the box and therefore often end up mis-diagnosing.
It is highly unlikely, no, let's say nearly impossible, that you "blew" the amp by "the stock amp giving you a bad signal". The only thing you will get from a bad signal is bad sound. The way an amp works is that it senses the voltage present at the input, and usually, (I'm generalizing and simplifying a bit)increases whatever voltage is there while simultaneously increasing output current capability enough to drive speakers. Insignificant current is delivered from the driving source to the amps input, so the driving source, in this case a BMW amp, dies not actually deliver "power" to the driven (PPI) amp. You need voltage x current to make power. A "bad" input will either:
1. simply give a distorted signal to work with. 2. cause the input stage of the amp to "clip", resulting in severe distortion, but no damage.
I suspect your PPI amp failed because of either just a random failure, or some other installation related problem such as overheating or an improper load impedance of the woofer. With most of today's good quality products, which is a category which certainly includes PPI, the occasional random failure is the most likely candidate. However, a bridged amp, driving a 4-Ohm woofer load would likely cause the amp to run very hot. I don't know what the impedance of your woofer was, but it is conceivable that failure was caused by overheating or overcurrent.
If you feed the input of the PPI amp with a signal taken from the speaker outputs of the BMW amp, you need a floating ground line output converter. If you take it from the input to the amp (Non DSP systems only) then you can connect this directly to the PPI with no special precautions. Both ways will wotrk fine as others who have done it will attest. There is quite a bit in the archives on audio you might wish to research.

Best regards,
Bob

: I had a PPI amp (360watt bridged) installed and a small 10" fosgate in a box. However within 2 days the amp and woffer both blew. First the amp then woffer. Both were replaced without cost to me. Anyways the shop told me my stock amp was giving a bad signal to the PPI so it was frying the amp when ever I played it too loud. They said if I wanted to keep the system I wouldnt be able to turn it up high! So I had them remove everything. Now is this a NAV amp design problem or do I have a faulty amp? Any ideas?

Follow Ups:

Bob this is over my head,Im going to print this show it to the stereo shopTHANKS!!... 00:21 6/03/2000 (0)

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