garychoffmann 10+ year member
CarAudio.com Elite
Well, I went out to my project car to work on the stereo. I installed my ppi a404 and a1200. Fired it up and a lower pitched pulsating hum coming out of all of the speakers. So I start trouble shooting. Voltage is great, grounds are extensively grounded. Head unit output is perfect. Everything checks out. I had the amps rebuilt about a year ago so I thought maybe its an amp issue. Hooked the amps up in my truck and they sounded beautiful. Took my directed 1100d5 and put it in my car.. it sounded perfect. Took the ppi's out of the truck and back in the car. Noise is back. I drop the amps off at the guy who rebuilt them and had him test them. Checked out perfect. So I check for an rca issue and voltage/sine look perfect. To double check I use my Yamaha receiver and run rca's to the amp. Hum is there still. I'm stumped so I start swapping in other amps. Put in a t2500.1, a600, phoenix gold 475ti, junk Sony 4 channel, a cobalt 260. Everything worked perfectly. Now here is where it gets interesting. I put another a404 in there and it was a little better but was there. Put in an old ppi sedona and it was there. Sooo my conclusion. Ppi hates my car. I can run anything but these ppi's. Any ideas? I'm plum out.