BimmerFest BMW Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter · #1 · (Edited)
Hoping for some help, if others have solved this problem before. I installed a new JL Audio XD600 amp with Technic's amp kit (great kit by the way) and I'm getting a hissing noise through the system - if there is even a tad bit of gain added. The noise is present even when the car/radio/volume is off and is constant regardless of volume. I can't be the only person who's had this problem, sadly search didn't bring up anything definitive.

The problem is not the amp, it's definitely caused by the signal coming from the factory head unit (or the wiring). I ran RCA's to the amp from another car's CD player (bypassing the factory input)... and there was no noise, it was crystal clear. So it's definitely not the speakers or the amp.

I've got to get this noise cleaned up, so I can use at least a little bit of gain, and I don't want to replace my factory head unit. So, my question is - will an Audio Control LC6i fix my problem (I've heard it mentioned before)? Is there a cheaper alternative? I like good sound but I'm not an audiophile - I just want to get rid of this noise.
 

·
Registered
Joined
·
2,693 Posts
I'm not so clued up on the very latest OEM head units in BMW's but I suspect you need a processor which accepts the factory speaker outputs and 'cleans' up the signal prior to going to your JL Amp. The JL signal summing unit and then the cleansweep unit's would acheive this and you already have a JL amp so perhaps look at those first. Other such products which do similar things are the JBL MS8, the Alpine PXA 800 (I think thats the new model number!) the audison bit one, amongst a few others :)

Have a little research online, then nip to your local dealer and installer to get one fitted up!

cheers, Dennis!
 

·
Registered
Joined
·
8,180 Posts
Hoping for some help, if others have solved this problem before. I installed a new JL Audio XD600 amp with Technic's amp kit (great kit by the way) and I'm getting a hissing noise through the system - if there is even a tad bit of gain added. The noise is present even when the car/radio/volume is off and is constant regardless of volume. I can't be the only person who's had this problem, sadly search didn't bring up anything definitive.

The problem is not the amp, it's definitely caused by the signal coming from the factory head unit (or the wiring). I ran RCA's to the amp from another car's CD player (bypassing the factory input)... and there was no noise, it was crystal clear. So it's definitely not the speakers or the amp.

I've got to get this noise cleaned up, so I can use at least a little bit of gain, and I don't want to replace my factory head unit. So, my question is - will an Audio Control LC6i fix my problem (I've heard it mentioned before)? Is there a cheaper alternative? I like good sound but I'm not an audiophile - I just want to get rid of this noise.
Using the fader and balance adjustments in your OEM HU determine which RCA output is causing the hiss. Also, post the XD settings. The #1 cause of hiss is the amp gain level.

The OEM HU outputs a balanced signal, flat and full range. The XD amp, as all the JL Audio amps, accepts balanced signals directly.
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #4 · (Edited)
The noise comes from all channels, and the noise is present even with no gain at all. Having said that, there really needs to be about 1/4 - 1/3 gain to drive the speakers the way they should be. Honestly, this whole "turn your gain all the way down" thing just to make the noise bearable is just not acceptable. Why people would be OK with even a little bit of hiss (in a nice car) is beyond me. I find it likely the hiss was there with the factory amp as well, it was just not noticeable until the power was increased. I'm probably going to run shielded RCA cables from the HU back to see if it clears up. Let me say again, there is absolutely no noise when using a HU installed in another vehicle (running a long RCA) to power the amp/speakers in this one. Of course, it was also a $1500 Kenwood Excelon with a regular (non-balanced) output.

I can't help but to assume that this whole balanced input thing is either garbage, or just doesn't work well with the XD amps. It accepts the input, but perhaps it doesn't do it well. I dunno.

The only things I can think of are:

1. The signal from the factory HI-FI head unit is trash.
2. Noise is introduced into the factory stereo wiring on the way back to the trunk. It's not shielded, it's supposedly magically protected due to the balanced differential signal.
3. The XD amp accepts 4v max inputs, the factory HU puts out 5v. Perhaps that's too much, then again maybe that's at max volume (I'm not sure). Having said that, I don't see how a line driver would help, it would only increase that 5v and I'd need even less amp gain to remove noise (which I can't take lower).

I'm just kicking ideas around here, wondering what the real problem is, and I think it's crap that everyone is happy with "just turn your gains all the way down" - I mean, really? From what I've been trolling across online this seems to be a very common issue, and simply turning the gain all the way down so there's only a little bit of hiss (when you put your ear to it) - while at the same time forcing us to not drive our speakers hard enough (aftermarket components in front, stock in rear) doesn't seem like the right solution.

If I could match the factory HU to AMP sensitivity with zero gain, that'd be fine - but that's not the case. I can't turn the gain backwards, so something is wrong.
 

·
Registered
Joined
·
8,180 Posts
The only things I can think of are:

1. The signal from the factory HI-FI head unit is trash.
Most probably your OEM HU outputs are trash. BMW changed the OEM HU from MY2010 to make them cheaper, at least that's my conclusion after working/installing MY2010-on OEM HU. They cannot be coded as before, they cannot accept the Sirius tuner as before.

However, the last MY2010 OEM HU with HiFi install with the exact same harness as yours but with a JL Audio HD900/5 did have absolutely no hiss or noise.

2. Noise is introduced into the factory stereo wiring on the way back to the trunk. It's not shielded, it's supposedly magically protected due to the balanced differential signal.
Hiss does not work like that... what is your ground point?

3. The XD amp accepts 4v max inputs, the factory HU puts out 5v. Perhaps that's too much, then again maybe that's at max volume (I'm not sure). Having said that, I don't see how a line driver would help, it would only increase that 5v and I'd need even less amp gain to remove noise (which I can't take lower).
The 5V OEM signal is fine with all the JL Audio amps. No line driver will help you with inherent hiss in the original signal, if anything it will make it worse.[/quote]

I'm just kicking ideas around here, wondering what the real problem is, and I think it's crap that everyone is happy with "just turn your gains all the way down" - I mean, really?
Yes, really. Either there is a gain problem -be your particular OEM HU outputs or your XD gains- or a ground problem somewhere. By the way, when you use another HU outputs (not installed in your car) and there's no noise what you have proven is that by isolating the ground the noise goes away, not necessarily that the OEM HU outputs are bad.

From what I've been trolling across online this seems to be a very common issue, and simply turning the gain all the way down so there's only a little bit of hiss (when you put your ear to it) - while at the same time forcing us to not drive our speakers hard enough (aftermarket components in front, stock in rear) doesn't seem like the right solution.
Yes, hiss is a common issue when either the amp gains or the ground are not properly done. Very seldom but very possible is a bad amp (I went thru two PDX amps due to hiss) and/or HU output, but only after the other two possibilities are fully eliminated.

If I could match the factory HU to AMP sensitivity with zero gain, that'd be fine - but that's not the case. I can't turn the gain backwards, so something is wrong.
Definitely something is wrong, and if the hiss is constant at all 4 channels then the next step could be changing the ground point: try the ground point on the side of the left fender, just above the OEM amp location.
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #6 · (Edited)
Interesting development, I just noticed that when using the radio, Sirius, etc. there is no noise. Only when listening to a CD. In fact, now that I listen closely, I can hear the distinct sound of the cd spooling up in the speakers.

So, no noise at all when listening to the radio even with the gain turned most all the way up (to test). All of the noise is coming from the CD player. No factory cd changer either, by the way. I've ordered a Dynavin nav head unit, so it'll probably go away once that's installed. Figured it was worth posting an update though.

PS - this is a HI-FI in a 2009 335I, it's not MY2010.
 

·
Registered
Joined
·
4 Posts
I had noise after installing Audison amp with stock head unit mated with Technics harness . I still have noise after installing Dynavin. I'm assuming unshielded lines from the whatever source to the trunk. Gain on Audison is all the way down and noise is still noticeble.
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #8 ·
Update: I've got no noise at all now. Dynavin head unit installed along with running shielded RCA's to the back.
 

·
Registered
Joined
·
4 Posts
I know this is an old thread but I think I can share some helpful info - I had this same problem with a similar setup (2011 328i / e90 + technic harness + JL XD600/6) and after banging my head on the wall for weeks here's what fixed it for me -

I took out my head unit (lots of videos on youtube) and wiggled the two big cables that plug into the back right of it. I assume one is antenna and the other is power or ground. With my wiggling I could hear the noise come and go, so I wrapped them in some electrical tape and put the head unit back with the cables in a position/tightness that did not cause noise. So far so good!

It's important to note that you should first diagnose if your problem is coming from before or after the RCA<->AMP connection by unplugging the RCAs and listening, and also plugging in a different source and listening. Hope this helps!
 
1 - 9 of 9 Posts
Top