Hi all. I have a 2011 MC with HK upgrade to which I've added a Line-Out Converter, Amplifier and Subwoofer (Audio Control LC2i, Alpine MRV M500, and Alpine 10D4). I have been experiencing what seems like an attenuation of the low end signal in the beginning of a song and during playback sometimes which I am unable to identify and is driving me CRAZY! For example, a song will begin, bass line starts at a low level for a few seconds, then it seems to "kick-in" and sometimes during a song if there is a lul in bass line (hope that makes sense). I've swapped out the LOC for a new LC2i and the amp (had an Alpine MRP M450) and am getting the same result. I haven't tried going directly into the amp at line-level, but I don't think it's the LC2i processing the signal. I suppose I should give it a quick try...... Any case, I got the pinouts for where I tapped signal at the HK amp from the BMW Online Service System as follows:

Right Rear (preamp)
+ Pin 8 (Grey/Purple)
- Pin 16 (Grey/Yellow)
Left Rear (preamp)
+ Pin 37 (Blue/Brown)
- Pin 29 (Blue/Black)

I'm pretty confident I hit the right spots for signal, so I'm kind of baffled. I wouldn't have thought there would be any processing on a preamp signal, but maybe I'm wrong?
I contemplated picking up the x9331 adapter from Integral Audio to simplify the connections, but I'm not sure that will solve my issue. Any thoughts or help is greatly appreciated!!

 

A couple quick thoughts:

-Those pins look correct, though you might have the polarity reversed (I have the F30 diagram in front of me, it's possible the R56 is opposite but they tend to be consistent). That wouldn't cause the issue you describe though.

-Check the integrity of the connections. If you have an intermittent connection to one of the +/- of the balanced signal you could have level fluctuations.

-Start simple: remove as much as possible from the signal chain. Test. Keep adding things until you've found what's causing it, then dig in.

Good luck. Let us know how you make out.

 

Swap the Audio Control LC2i to another type LOC, and see if you're problem goes away.
This unit has some form of bass compensation that might be an issue for your system.

Reading the manual, it looks like it uses a compressor/expander circuit for bass compensation.

 

Per the original post he's already tried a different LOC.

 

He's swapped like for like.

The LC2 does bass compression/expansion.

His issue sounds like compression gone wild.


He needs a basic LOC to rule it out.

 

I stand corrected.

 

Thanks for the ideas. I'll do some testing this weekend and report back. I hope it's not the LOC because I mounted the level **** in the drivers side knee roll and I really love it. Any case thanks again!

 

Have you read the manual and set the LOC's "Bass compensation" to a neutral setting.

That seems like a dangerous function.

 

I haven't messed with the bass compensation settings, but it appears I will need to...
Appreciate the help!!!!

 

Hi all. Sorry for taking so long to report back. I checked over all my connections etc and it turned out to be the bass compensation on the LC2i. I tweaked it so there is no drop off and it sounds 100% better. Thank you for the help and feedback!!!