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Can HU be source of speaker hiss?


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Just finished installing audio setup in a 03 RSX and there's some significant speaker hiss...

 

How everything is set up

- HU (Jensen $50 special 2v preouts)

- 2 ch Twisted pair RCA ran HU to amp (not ran anywhere near the power cable)

- remote on is tapped from HU to car Ant wire

- amp is 5ch ran to 4 speakers and a sub

- rewired all speakers direct to amp (not using factory wiring at all)

- let me know and I can get much more specific

 

What I've tried:

- improved amp ground - filed off all paint and tightly grounded to chassis with bolt. 4 ga wire under 13" from amp.

- unscrewing amp mounting makes no difference.

- grounded HU to chassis instead of using harness ground (eliminated the slight alternator whine I had initially, but does not fix hiss.

- took out the HU and ran an RCA direct to the amp with a different RCA (not running through any trim) no change

- tried RCA noise filter. No change

- tried grounding the RCA cables to the HU and to the chassis. No change.

- radio antenna in or out makes no difference.

 

Symptoms:

-hiss only comes through tweeters

-gain is set at MINIMUM on amp and hiss still well audible

-does not change with increased volume on HU, but gets louder with increased amp gain

- if I unplug the RCA inputs it goes away and there's no hiss even with increased amp gain.

- hiss is no different with car on or off

 

Most things I've read say it's a amp gain issue, but my gain is literally at minimums and the hiss is still significant. Without the RCAs plugged in I can max out the gain and hear a barely audible hiss but that's def not the issue. Basically I feel like I've trouble shot it all the way back to the HU. I wanted a sanity check before I give up and buy a new less cheap HU. Does the voltage of the pre outs matter for this issue?

I'm out of ideas. Please help.

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TLDR: it's confirmed the HU causing hiss

 

Update:

I connected the amp direct to my phone with an RCA to 3.5mm as mentioned above. (Connected at the end of the RCA that normally plugs in to the HU so it's still running through all the car trim). 

 

No hiss at normal levels (barely audible at max gain with my ear next to the speaker)

 

So I think that confirms the HU is the issue. Which I'm not too upset about since it was only $50. (Jensen MPR2121). I guess if you're going to spend a ton of money on a sound system you probably shouldn't skimp on the HU..

 

Thanks Joe X for the idea

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