Hiss from aftermarket audio upgrade?

Krzysiek · 03-12-2016, 03:48 PM

I'm trying to upgrade the audio system in my E91 with the HiFi option. Got a harness for p&p connected to Alpine PDX-5 that was causing a very noticeable hiss from the tweeters. Those amps being fairly famous for the noise, I picked up a PDX-V9 recently and still have the same issue.
Amp is plugged in to the battery and grounded to the factory spot on the left rear wheel well.
Hiss is there on each and every RCA connection (front/back + left/right) and minimum gain setting. Plugging in a ipod/phone to thet amp directly results in barely audible hiss at nominal gain.

Any ideas what could be the culprit? Perhaps the head units output is just garbage?

ctuna · 03-12-2016, 05:44 PM

You could try injecting another source into the amp to see if the radio or idrive is the problem. You don't have the gain turned up to high do you?
If you are using the stock speakers which are 2 ohm you pretty much
can't have any gain on the 2 ohm door speakers with an amplifier that feeds them aftermarket power.
There was a run of radio's that had noise problems.
Generally that would show up with the stock setup.

tdgesq · 03-12-2016, 05:56 PM

Do the PDX have balanced inputs? That is required for the hi-fi signal.

Krzysiek · 03-12-2016, 06:10 PM

Quote:

Originally Posted by ctuna

You could try injecting another source into the amp to see if the radio or idrive is the problem. You don't have the gain turned up to high do you?
If you are using the stock speakers which are 2 ohm you pretty much
can't have any gain on the 2 ohm door speakers with an amplifier that feeds them aftermarket power.

Very little hiss from other source. Gain is set at minimum.
I just installed the MB Quartz speakers, hiss is still present.

Quote:

Originally Posted by ctuna

There was a run of radio's that had noise problems.
Generally that would show up with the stock setup.

I may need to dig out the stock amp then, but I don't remember any problems running it. Maybe just didn't listen close enough.

Quote:

Originally Posted by tdgesq

Do the PDX have balanced inputs? That is required for the hi-fi signal.

I believe so. I think it's quite a popular amp upgrade here. The first version had a bad run with some hissing by themselves, but the second gen should be all good according to google.

tdgesq · 03-12-2016, 06:16 PM

Does it stop hissing when you unplug all inputs to the amp?

Krzysiek · 03-12-2016, 07:29 PM

Yes. No hiss whatsoever w/o RCA.

Doing a bit more googling suggest the issue might revolve around "balanced differential inputs" that the Alpine doesn't seem have. Would a LOC help?

tdgesq · 03-13-2016, 12:41 PM

So it is the input signal. It could either be a bad head unit or that the PDX cannot accept a differential-balanced signal. The first thing to do is hook the hi-fi amp back up and see if the noise is still present. If it isn't, then your PDX is having trouble processing the signal.

A regular LOC will not help as they are designed to simply step-down voltage. They do not have the circuitry to process the signal. Rockford Fosgate did sell some line driver stuff (three-sixty?) that might work. Call them first to make sure it will do what you want it to do. I believe the hi-fi output from the head unit is 5 volts.

Krzysiek · 03-13-2016, 02:13 PM

I was thinking about getting the Audiocontrol Matrix Plus for the job if I can find it somewhere in the EU.

I checked the RF and the base unit has only 2 outputs, which might be a limiting factor at some point and the higher level ones add quite a bit of complexity and cost that I don't need at this point probably.

taibanl · 03-13-2016, 02:22 PM

You have a defective oem hu.

Krzysiek · 03-13-2016, 02:35 PM

I remember reading a post about BMW switching HU manufacturers (to Alpine?) in 2009 or so that resulted in quality issues, but mine is 2006 and I think made by Harman (old school Business Navigation with arrows) so thought I'm in the clear.
Might push me into looking for a CIC retrofit...

taibanl · 03-13-2016, 03:14 PM

Quote:

Originally Posted by Krzysiek

I remember reading a post about BMW switching HU manufacturers (to Alpine?) in 2009 or so that resulted in quality issues, but mine is 2006 and I think made by Harman (old school Business Navigation with arrows) so thought I'm in the clear.
Might push me into looking for a CIC retrofit...

Hmm. Ok. Missed that. But maybe worth the cic uograde

joeyc123 · 03-14-2016, 01:35 PM

I've got the same amp (PDX V9) and have a hiss as well, my gains are set pretty low. When the volume is turned up there is some sort of ticking as well.

I had a JL 700/5 previously and had the same hiss as well. From my understanding I thought both of these amps accepted balanced differential inputs.

Krzysiek · 03-19-2016, 04:02 PM

I've plugged in the oem amp and hiss is still there. It's also audible from the underseat woofers, so quite a wide range. Guess I'll be looking for a new HU.

OnlyDriveGerman · 03-19-2016, 04:14 PM

Usually due to a bad ground. Check that out.

Krzysiek · 03-20-2016, 02:59 PM

Unplugging the RCAs from the amp and pluging in my phone cures the hiss, so that should rule out grounding issues, right?

03-12-2016, 03:48 PM	#1
Krzysiek New Member 0 Rep 9 Posts Drives: E91 Join Date: Jun 2012 Location: PL iTrader: (0)	Hiss from aftermarket audio upgrade? I'm trying to upgrade the audio system in my E91 with the HiFi option. Got a harness for p&p connected to Alpine PDX-5 that was causing a very noticeable hiss from the tweeters. Those amps being fairly famous for the noise, I picked up a PDX-V9 recently and still have the same issue. Amp is plugged in to the battery and grounded to the factory spot on the left rear wheel well. Hiss is there on each and every RCA connection (front/back + left/right) and minimum gain setting. Plugging in a ipod/phone to thet amp directly results in barely audible hiss at nominal gain. Any ideas what could be the culprit? Perhaps the head units output is just garbage?
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03-12-2016, 05:44 PM	#2
ctuna Lieutenant General 1923 Rep 13,131 Posts Drives: 325xi 06 wagon MT Join Date: Jan 2010 Location: Santa Cruz, Ca iTrader: (0)	You could try injecting another source into the amp You could try injecting another source into the amp to see if the radio or idrive is the problem. You don't have the gain turned up to high do you? If you are using the stock speakers which are 2 ohm you pretty much can't have any gain on the 2 ohm door speakers with an amplifier that feeds them aftermarket power. There was a run of radio's that had noise problems. Generally that would show up with the stock setup.
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03-12-2016, 05:56 PM	#3
tdgesq Private First Class 4 Rep 145 Posts Drives: 335xi Join Date: Feb 2012 Location: Pacific N.W. iTrader: (0)	Do the PDX have balanced inputs? That is required for the hi-fi signal.
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03-12-2016, 06:16 PM	#5
tdgesq Private First Class 4 Rep 145 Posts Drives: 335xi Join Date: Feb 2012 Location: Pacific N.W. iTrader: (0)	Does it stop hissing when you unplug all inputs to the amp?
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03-12-2016, 07:29 PM	#6
Krzysiek New Member 0 Rep 9 Posts Drives: E91 Join Date: Jun 2012 Location: PL iTrader: (0)	Yes. No hiss whatsoever w/o RCA. Doing a bit more googling suggest the issue might revolve around "balanced differential inputs" that the Alpine doesn't seem have. Would a LOC help?
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03-13-2016, 12:41 PM	#7
tdgesq Private First Class 4 Rep 145 Posts Drives: 335xi Join Date: Feb 2012 Location: Pacific N.W. iTrader: (0)	So it is the input signal. It could either be a bad head unit or that the PDX cannot accept a differential-balanced signal. The first thing to do is hook the hi-fi amp back up and see if the noise is still present. If it isn't, then your PDX is having trouble processing the signal. A regular LOC will not help as they are designed to simply step-down voltage. They do not have the circuitry to process the signal. Rockford Fosgate did sell some line driver stuff (three-sixty?) that might work. Call them first to make sure it will do what you want it to do. I believe the hi-fi output from the head unit is 5 volts.
	Appreciate 1 Quote

03-13-2016, 02:13 PM	#8
Krzysiek New Member 0 Rep 9 Posts Drives: E91 Join Date: Jun 2012 Location: PL iTrader: (0)	I was thinking about getting the Audiocontrol Matrix Plus for the job if I can find it somewhere in the EU. I checked the RF and the base unit has only 2 outputs, which might be a limiting factor at some point and the higher level ones add quite a bit of complexity and cost that I don't need at this point probably.
	Appreciate 0 Quote

03-13-2016, 02:22 PM	#9
taibanl Brigadier General 281 Rep 4,121 Posts Drives: BMW Join Date: Sep 2010 Location: NA iTrader: (4)	You have a defective oem hu.
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03-13-2016, 02:35 PM	#10
Krzysiek New Member 0 Rep 9 Posts Drives: E91 Join Date: Jun 2012 Location: PL iTrader: (0)	I remember reading a post about BMW switching HU manufacturers (to Alpine?) in 2009 or so that resulted in quality issues, but mine is 2006 and I think made by Harman (old school Business Navigation with arrows) so thought I'm in the clear. Might push me into looking for a CIC retrofit...
	Appreciate 0 Quote

03-14-2016, 01:35 PM	#12
joeyc123 Private 7 Rep 95 Posts Drives: 2007 328i Join Date: Dec 2013 Location: Los Angeles, California iTrader: (0)	I've got the same amp (PDX V9) and have a hiss as well, my gains are set pretty low. When the volume is turned up there is some sort of ticking as well. I had a JL 700/5 previously and had the same hiss as well. From my understanding I thought both of these amps accepted balanced differential inputs.
	Appreciate 0 Quote

03-19-2016, 04:02 PM	#13
Krzysiek New Member 0 Rep 9 Posts Drives: E91 Join Date: Jun 2012 Location: PL iTrader: (0)	I've plugged in the oem amp and hiss is still there. It's also audible from the underseat woofers, so quite a wide range. Guess I'll be looking for a new HU.
	Appreciate 0 Quote

03-19-2016, 04:14 PM	#14
OnlyDriveGerman Lieutenant 179 Rep 527 Posts Drives: 2007 328xi Coupe 6MT Join Date: Dec 2014 Location: New Haven County, CT iTrader: (1)	Usually due to a bad ground. Check that out.
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03-20-2016, 02:59 PM	#15
Krzysiek New Member 0 Rep 9 Posts Drives: E91 Join Date: Jun 2012 Location: PL iTrader: (0)	Unplugging the RCAs from the amp and pluging in my phone cures the hiss, so that should rule out grounding issues, right?
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