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Old 14th December 2009, 20:48   #1
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Default Whatzatt Noise (Hissing sound)

Hello guys, need your help in cracking this up. I've been recently hearing a lot of background hiss in my system ever since I bumped the gains a bit up (the tweeters seem to be always a bit extra powered than the mid-bass somehow). The hiss is audible only when a track starts playing or gets more pronounced during a song playing (silent periods within a song for example), but I can even hear it when music is played.

The real deal- I still hear a hiss when I bumped the gains down, and the level of hiss doesn't change much whether I am listening at vol 1 or vol 14. What's more, the hiss gets more pronounced when playing a CD compared to MP3s (via USB). Now I even hear some funny scratching sound (almost like scratching a vinyl disc on a turntable) on top of it when I reverse a song to its start (both in CD and in USB mode). It's almost like hearing the innards of the head unit.

I am using Clarion DXZ785USB, JBL 1004 Amp, Illusion Electra speakers, JBL wiring kit (original), Illusion speaker wires. The RCA cables are routed on one side and power+speaker wires are from the other side of the car.

Now here are my questions:

1. This is not a problem with the gains right? If the gains were higher, one would hear the same hiss when tracks change, but the hiss disappears completely for a brief millisecond when a track changes, so this is no gains issue?

2. Combining this with the brief scratching sound- is it normal, or is the HU at fault here?

3. Is this whole hiss thingy expected? From Crutchfield Tech Support: I can hear a hiss in the speakers after I installed my new car stereo system.
Quote:
It is common, after replacing a factory receiver with a high quality aftermarket receiver, to notice a background hissing sound. The "hiss" is nothing more than the extended frequency response of the new stereo, and not a defect, or wiring problem.
4. Any other suggestions, tricks or advice will be greatly appreciated! Thank you in advance!
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Old 14th December 2009, 21:15   #2
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Is this only when your engine is on or always?
If it is only with the engine on it means a ground loop has been created.
Ground loops are caused by a mismatch in the ground potential (voltage)
between two sources. Current flows through the shield of the RCA cable and is quickly picked up by the amplifier.


This is what you should do-
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Old 14th December 2009, 21:51   #3
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Thank DJNik, but the problem is equally there when the engine is off. So definitely no alternative whine/grounding loop issue is this.
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Old 14th December 2009, 22:04   #4
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Your description of the "hiss" seems very different from what is typically seen in most setups.

Since you said the hiss increased when you bumped up the gains, I thought it must be due to noise that the RCAs are picking up along the way. But this usually goes away if the engine is turned off. Still, take some other good RCA cable and try running is straight from the head unit to the amp (without routing it through the channels etc). Also tell us what happens if you remove any 2 of the 4 RCAs, i.e. run only front or rear channels.

Everything else points to some issue with the head unit, or the files you are playing. Check with another head unit if you can.
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Old 14th December 2009, 22:12   #5
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Thanks Ajay, I always knew mine was a different hiss From what you are saying, this could be RCA or HU issue. Tell me, does one expect to hear any level of hiss from a well-tuned system (as hinted at by the Crutchfield article quoted above)?
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Originally Posted by Bass&Trouble View Post
Also tell us what happens if you remove any 2 of the 4 RCAs, i.e. run only front or rear channels.
Does it matter where I remove RCA plugs from, the amp or the HU? If not, I can easily access my amp and take this test right now.
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Old 15th December 2009, 13:33   #6
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Quote:
Originally Posted by greenh0rn View Post
Thanks Ajay, I always knew mine was a different hiss From what you are saying, this could be RCA or HU issue. Tell me, does one expect to hear any level of hiss from a well-tuned system (as hinted at by the Crutchfield article quoted above)? Does it matter where I remove RCA plugs from, the amp or the HU? If not, I can easily access my amp and take this test right now.
I don't know what Crutchfield is referring to. In high-quality aftermarket stereos, there should be absolutely no added noise. How is it high-quality otherwise.

You can remove the RCA cable from any end. Just don't remove it with the HU playing, and keep them apart from each other and away from any metal. And while you're at it, just try reducing the gains and observe very carefully whether the noise level goes down.
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Old 15th December 2009, 21:06   #7
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The scratching sound while skipping tracks suggests there may be an issue with the HU.
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Old 26th December 2009, 15:04   #8
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Hey B&T, guys, I finally found time to test and tweak the sound today- guess reducing the gains around 10-degrees did the trick (say from --:57' on the clock to --:47')- the noise at silent passages is now barely barely audible, very close attention reveals it but at least it is gone down way below than it was before. So, it WAS a gains-set-too-high issue!
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