Hiss on startup, only goes away after toggling switches?

[Will Sanders]

I just installed a PPI 900.5 in my vehicle. I used 6 gauge wire and a 50A fuse, plus twisted RCA cables. When I turn on the vehicle or just put it in ACC mode, there is a very loud hissing sound coming through the speakers. This sound continues when I unplug the RCA cables. It only stops when I toggle the "Input Select," "LPF/HPF/Full," and "HPF/Full" switches along the top of the amp (see photo). One switch must be toggled for the front speakers, and another must be toggled for the rears. The hissing also stops once music starts playing. What could be causing this? I grounded the amp to a metal bracket in the cabin. Not sure if that would make a good ground.

The amp also gets pretty warm, even just sitting on the seat after five minutes of light use. This seems abnormal because it is a class D amp and isn't being pushed very hard.

Let me know what you think...

Click to read more...

 

[wew lad 5,000+ posts]

my ppi900.4 stays pretty warm even at idle as well, it's normal imo especially in fl and hot humid climates.

I would start by regrounding your amp to the thickest piece of metal you can find connected as close to the amp and main cabin of your car as possible, make sure the ground is properly sanded and clean. use a bolt that secures the wire tight. if nothing changes I would consider checking that your rcas aren't run near any power wire or look at the amp for being defective.

 

[Will Sanders]

Just tried connecting the ground to a more metal-dense area and no change to the hissing whatsoever. I'm not sure if this means anything, but when I lift up one side of the amp by about 2 inches and drop it on the carpet, the sound stops. Is something loose?

I also tried powering up the amp without the RCA cables connected. Still no change. If you disconnect and reconnect the RCA cables while the amp is running, the hissing will stop. The hissing also changes a little when you rub the RCA cable against the RCA output from the head unit.

I know the head unit works because it's brand new. I also used it with another amp that I had to return because it was too big. I'm really confused.

 

[wew lad 5,000+ posts]

Sounds like a defective amp to me, plug in rcas directly from a separate source to confirm the problems not up the line. Use a cheap aux to rca from your phone directly into the amp.

 

[dev199505]

Where is your amp mounted? And does it have metal or plastic feet? If you have a ground loop somewhere it could be causing the noise

Sent from my HUAWEI Y536A1 using Tapatalk