So over the weekend i decided to amp the stock car speakers on my MY11 WRX.

Ive used a new Kenwood amp 40w rms x4ch located under the passenger seat. I know stock speakers are only rated at 20-25w rms, but the amp is not outrageously gained or running at distortion.

My problem though is upon starting my car after not having run for a few hours (ie over night or after work) that im getting alternator hiss through the speakers until the car has warmed up a little (about 45seconds or so) then the noise disappears/becomes considerably quieter.

i have checked the ground on the amp, and have use a bolt near the aircon vents under the passenger seat, and even sanded the metal down for good measure.

I am using a hi-level to rca converter for the audio signal, and have all cables running though the centre of the car away from the power cables to the amps.

The audio quality and level does sound a lot better though, its only this small interference thats bugging me.

If it means anything else, this is the second amp in the car, the first being a 1000w rms JL amp located in the boot.

Any other ideas? i still have no clue what may be causing it.

Still oem head unit?

Having a quick read online it could be a few things;

The oem head unit might have a high noise floor (whatever that means)

If you ground is good on both amps I would suggest re-grounding the head unit.

Are you using a Rca splitter or 2 seperate runs?

And amp gains...

That's all I can think of...


Ps I'm not a fan of the high level to low level converters as I have heard they can be troublesome...


using the Perth-WRX mobile app

__________________
2005 WRX STI

adjust gains on the rca, make sure all wires are soldered and none are frayed, adjust gains down or alternatively get a powered processor

__________________
363hp and 499.5nm
gtps03 turbo on 98ron BP
2012 Wrc Blue Wrx Sti R spec (ARGH SPEC)

High Noise floor means that the electrical noise of the system is "high" in comparison to the max output signal levels. This is the reason that high level outputs were developed, say 2V max output v 5V max output to put a greater electrical difference between the "noise floor" and signal output. Also note that max is not norm or average voltage by any sense.

The fact that the "hiss" takes a while to occur and then disappears is bizarre.

OP is there any other info you can give about when it occurs.

RCA splitters are also not good for sound quality as your splitting the electrical input between amps. Essentially, you want your input as hot as possible (or as high as possible) without input distortion at the amp and amp gains as low as possible to limit amplifying the noise floor.

Fianlly, ALWAYS over amp v speaker output. It's under amping that causes clipping which kills speakers as most won't hear it where as over excursion of a speaker due to over amping is obvious. I used to run my recording studio monitors rated at 60W RMS with Crown mono block amps rated at 300 W RMS and 600 PEAK.

__________________
[COLOR=Black]Liberty GT Spec B tuned 240 HP & 372 Nm at the hubs.[/COLOR] "Instead of banning high performance cars - ban low performance drivers"

What line level converter are you using and where did you install it? They're fairly susceptible to noise as it is. Also triple check your polarities going into it.

__________________
[I]trolololol[/I]

I'll do abit more investigating tomorrow and check if it's coming from any speakers in particular or all of them.
Yes it is the oem navigation HU. I've got all 4 speakers running down the centre of the car as much as possible to a line converter located next to the amp under he passenger seat. As for brand of the line converter, at the moment it's the stock standard brand from most auto shops (aeropro??) which I had installed on the girlfriends veloster the weekend before with the exact same setup and same brand/rated amp and there's no problems with here.

I had originally tried to use the hi level input plug that came with the amp but I was getting even worse hiss (wouldn't go away and was louder) so that's why I went with the line converter.

Has anyone used a noise filter? I've never had this problem before on any other car so I've never tried the filters.

Over the weekend I'll triple check grounds and the converter levels.

Thanks for all the input so far

And yes all connections at are soldered and insulated.

There is no RCA splitter other than through the amp, I've got the signal going to the mono block in the back, then out the preamp to the amp under the seat. I had to go this way as ken wood thought it was a good idea not to have a preamp output on their amp :/