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00 BRP RS Coupe
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Discussion Starter #1
I've had my RS for 15 years now, and no matter what head unit's in the dash, or speakers in the doors/rear shelf, or amp (or amps) that I've ran... I get a constant hissing sound through the speakers.

It's a white/pink noise type of hiss that stays at a constant volume. If you pause the music, you can hear it. It becomes less pronounced as you turn the volume up cause it drowns out the hiss a bit - but I can still hear it. I've never heard it through any of the subs I've ever used.

My speakers have always been deck powered, then amp-powered, and have had 2 completely different brand and types of amps for them over the years. Troubleshooting over the years as well, I've ran 2 different types of in-line RCA ground loops isolators for the front and rear speakers to the amp(s). They either don't do anything or happen to be defective. Admittedly, they weren't the highest-end ones.

My car's not my daily anymore so it's not driving me crazy, but I'd still like to find a resolution. I have the same head unit in my daily Forester and never had any hissing regardless what speakers I've been running in there too.

Does anyone else have this issue!?!? Is it a quark of our cars or is it just me??
 

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1995 EZ30 Coupe
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I've noticed this issue when I've relocated the battery to the trunk and run my power cable too close to the radio/center console. I assumed it was a proximity thing anyway.
If you haven't run a battery cable close to your radio, I would think it to be a ground, but you've had ground loop isolators...

Try running shielded wire to the speakers? And check all the grounds you can find I guess. Good luck, keep us posted. I'm sure you're not the only one with this grievance.
 

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Discussion Starter #3
Ah, my battery's in the trunk too now (though I had a bit of a hiss when it was under the hood).

The power wire's running up under the driver's sill, and my RCA's down the middle. I could run it down the passenger side, but that'd mean pulling out the interior again :/ I'm wondering if it'd make a difference now cause my amp and it's RCA's & power wire are so close to each other and the battery...

I'm thinking "high end" ground loop isolators/noise filters, see how it goes...
 

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My battery is in my trunk as well, but instead of running a ground cable up to the front I drilled thru the floor in the trunk and ran 0g cable from the battery to the chassis. Haven't had any issues with hissing or feedback in the stereo. Plus I run 2 different power cables, one for the stereo and one for the car with a breaker on each line instead of fuses. All 0g cable/wire.
Hope that helps!

p.s. I've had my RS since '02... haven't seen a lot of people have their cars for as long as I have and you're probably the closest.

-Justin
 

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2001 RSTi, 2011 WRX Hatch
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How are your gains setup? Can your turn your headunit to max volume w/o any clipping from the amp?

Sometimes if you have the amp gain up too high, you can amplify any noise in the signal path or output circuitry of the headunit. You can get a lower noise floor by lowering the gain on the amp and using more of the volume knob on the headunit.

What voltage are the preouts on your headunit?
 

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Discussion Starter #6 (Edited)
My battery is in my trunk as well, but instead of running a ground cable up to the front I drilled thru the floor in the trunk and ran 0g cable from the battery to the chassis. Haven't had any issues with hissing or feedback in the stereo. Plus I run 2 different power cables, one for the stereo and one for the car with a breaker on each line instead of fuses. All 0g cable/wire.
Hope that helps!

p.s. I've had my RS since '02... haven't seen a lot of people have their cars for as long as I have and you're probably the closest.

-Justin
Ah, I can picture that. I guess I didn't wanna drill more holes in the floor.
From my battery in the trunk, I ran a 4g cable up to the hood under the driver's sill panels, and connected it to the main harness power wire and alternator wire with a distribution block. Power to/for the amp is coming off the battery's positive terminal (have battery terminals that allow for a few cables) by way of a 2nd 4g wire running just to it.

Yes! I too came in 2nd at a local 1st gen Impreza meet summer last year for ownership. Only guy that beat me was an actual, original owner.
 

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Discussion Starter #7
How are your gains setup? Can your turn your headunit to max volume w/o any clipping from the amp?

Sometimes if you have the amp gain up too high, you can amplify any noise in the signal path or output circuitry of the headunit. You can get a lower noise floor by lowering the gain on the amp and using more of the volume knob on the headunit.

What voltage are the preouts on your headunit?
I have my gains setup pretty high for the main speakers. I'll try your idea about turning down the gains for them, and using the deck's volume knob.
It's maxed out for the sub though :p I don't hear the hissing through it anyway, I believe the crossover happens to also filter it out. I'm running a separate gain knob for it for added control.

My deck has 4v pre-outs. Does the output make a difference?
As per my amp's setup instructions, it says to adjust the voltage to match the deck. Which I believe I did, but it's a little tricky. The dials for front and rear start at 600mV at around 7 o'clock and 6V at 4 o'clock, with no numbers in between; so it's a bit of a guess.
 

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Discussion Starter #8
BTW, ordered some fairly high end (I hope) ground loop isolators. They were fairly pricey anyway...
 

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Discussion Starter #9
Ordered some, supposedly, I hope, high end noise filters and a bit of shielded RCA wire.

Not installed yet. The car's ass end is up in the air right now getting some suspension work done. I'll try things out when the car's back on the ground...
 

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2015 Impreza seda
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i second the comment about the gains issue. but just saw your very recent post op. please let us know how the shielded rca wire/high end filter combo goes. i hope the issue gets fixed!
 

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Discussion Starter #11
I will play around with the gains again one more time. I'm pretty sure even with them turned all the way down, there was still a hiss. When the car's butt is back down on the ground I'll try again...
 

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Try running the signal cables as far away from the power wire, make sure your grounds are good including at the battery. Use as short as you can ground from the amp (less than 18”). I try to ground to an existing bolt in the car, preferably a seat belt bolt or seat mounting bolt. Induced noise is always a pain to fix. Hope you get it sorted.
 

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Discussion Starter #14
Try cleaning up the battery ground.
Grounds are nice and clean. I'm hoping that's something I've checked off the troubleshooting list properly...
 

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Discussion Starter #15
Try running the signal cables as far away from the power wire, make sure your grounds are good including at the battery. Use as short as you can ground from the amp (less than 18”). I try to ground to an existing bolt in the car, preferably a seat belt bolt or seat mounting bolt. Induced noise is always a pain to fix. Hope you get it sorted.
My RCA's and power wires are as far apart as I can get them with my setup.

Grounds are good and clean, though the battery and amp share the same grounding point - I removed the centre lap belt from the rear seat and re-purposed its anchor points.. I don't see that making a difference, but would it?

Power and ground cables for the amp is as short as possible too.
 

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You could also just have a noisy headunit or a noisy amp... it happens.

I always liked the older kenwood headunits because you can shut off the internal amp, which gave much cleaner ouput signal on the RCAs. Plus they have 5V RCAs, which offer much better noise floor too.
 

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Discussion Starter #17
Small update tonight:

Popped in the noise filters the other night, and ran the car today. Still hissing :/ About the same as before? Maybe a bit less (placebo effect)? I'll be playing with the gains as mentioned above when I have the chance.
 
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