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      07-15-2010, 06:59 AM   #1
sniffer
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335i Upgraded Audio - Interference Problem - Suspect HPFP

Hi,

Car had Europe stock audio. Took inputs from either side sill and installed amp in trunk.

Now get annoying interference, high pitched whistle type noise, always there, but if throttle applied, pitch increases slighltly afterwards, then goes back down again, if engine is at a constant RPM, so I suspect this is interference from something on the fuel sysem, likely the HPFP.

Has anyone had this problem??

I ran cables from each sill to the RHS of the trunk, cables run from RHS to LHS of trunk across in a loom with amp power (from battery), behind bluetooth module on trunk floor and then down the LHS of trunk to amp, installed in CD changer area at LHR rear of trunk.

As I said, power runs from battery along RHS of trunk, then down with the other cables across trunk floor and then along LHS to LHS rear of trunk where amp is.

Thanks for any assistance.,
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      07-15-2010, 09:58 AM   #2
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Thanks for the reply.

Thanks for the pointer about the LPFP. Does anyone know if this is variable speed?

It is not the alternator because the pitch of the noise is lagging and dependant on load, not RPM.

For example, 2000RPM, 5th gear, whistling noise constant, floor it for 5 seconds and then back off, noise stays same and then rises in pitch and volume a few seconds later, like it is dependant on fuel delivery loadings, albeit with a few seconds lag.

The pictures I have seen of the HPFP have a large cylindrical unit which looked like a small starter motor poking out the top of it.
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      07-15-2010, 01:01 PM   #3
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Is your amp set up to use differential Inputs?

the output of the head unit uses differential signals (not ground and hot) this is suppose to suppress noise but the amp has to use this kind of input(differential) to take advantage of it. More likely the noise is coming from the ignition system spark plug wires etc.
Be more specific in the type of amp you installed and the system you have

Last edited by ctuna; 07-15-2010 at 01:09 PM.
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      07-15-2010, 01:37 PM   #4
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Many amps will have RPM-related noise in BMW installs.

- What amp do you have?

- How are the sill wires (which are speaker wires) connected to the amp?

- How high is the input sensitivity?

- Where is it grounded?
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      07-15-2010, 03:09 PM   #5
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Quote:
Originally Posted by VP Electricity View Post
Many amps will have RPM-related noise in BMW installs.

- What amp do you have?

- How are the sill wires (which are speaker wires) connected to the amp?

- How high is the input sensitivity?

- Where is it grounded?
Hello, thanks for the reply;

Amp is a Vibe litebox 4. It is lovely, sounds awesome and fits beautifully into the car, except this noise.

Sill wires are connected to wire which I have run either side of car to amp. RHS wires cross over trunk where wiring for bluetooth runs to bluetooth module, then up and along with the LHS wires. Then split into parallel for front and rear RCA input channels on amp.

Input gain is set pretty high on all 4 channels.

It is installed under the CD changer area and grounded on the BMW grounding point on the LH rear arch.
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      07-16-2010, 01:14 AM   #6
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You have speaker wire signals connected to RCA inputs. That amp is really unlikely to have inputs that can accomodate BTL speaker level signals. Vibe amps are not common in the States and I don't know much about them, but I bet they do not have "balanced" inputs.

You probably need to lower your gains, and you may want to ground to the battery (I don't ever use those grounding brackets), and speaker level signals are NOT picking up the noise inductively.

You are hearing the noise because A) you are ruining your noise floor (by the way, if you are running speaker level signals in, your gains should be LOW, not HIGH), or B) you have an input problem (combination of ground loop and shorted speaker leads).

If you unplug all your RCAs at the amp and meter from one RCA shield to another, and get continuity, your shields are common, and that amp DEFINITELY can't take speaker level in.

If you don't get continuity, it may or may not be good at it.

Also, make sure trunk is assembled. Mechanical FP noise from trunk is audible if testing with R seat out/down...
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      07-16-2010, 03:36 AM   #7
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Quote:
Originally Posted by VP Electricity View Post
You have speaker wire signals connected to RCA inputs. That amp is really unlikely to have inputs that can accomodate BTL speaker level signals. Vibe amps are not common in the States and I don't know much about them, but I bet they do not have "balanced" inputs.

You probably need to lower your gains, and you may want to ground to the battery (I don't ever use those grounding brackets), and speaker level signals are NOT picking up the noise inductively.

You are hearing the noise because A) you are ruining your noise floor (by the way, if you are running speaker level signals in, your gains should be LOW, not HIGH), or B) you have an input problem (combination of ground loop and shorted speaker leads).

If you unplug all your RCAs at the amp and meter from one RCA shield to another, and get continuity, your shields are common, and that amp DEFINITELY can't take speaker level in.

If you don't get continuity, it may or may not be good at it.

Also, make sure trunk is assembled. Mechanical FP noise from trunk is audible if testing with R seat out/down...
Thanks for your help.

I tried re-running the power from battery last night, rather than going all the way round the trunk and across the floor with all my other cables, I ran across the rear under the trunk latch. Seems to have helped a little, probably a 33% reduction in the noise.

The Vibe amp can handle hi level inputs, there is a switch underneath it to change the input sensitivity.

I think this may be due to the gain settings. Will have a go at adjusting them down. I have the gains set at around 60 - 80 percent on front and rear channels.

Thanks again. I will post back when I have done it to let you know how I get on.
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      07-30-2010, 06:59 PM   #8
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Just to update:

Adjusted gain down and now almost eliminated noise completely.

So problem seemed to be a combination of the power lead run and the gain.

Many thanks to all, especially VP.

Last edited by sniffer; 08-06-2010 at 07:36 PM.
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      12-06-2012, 04:09 PM   #9
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In order to help others who may experience the same issue, I am trying to eliminate the interference issue on this thread which has resurfaced now I have coded my HU to Hi-Fi for low level, non molested by EQ, inputs to my amp

Details on the enclosed thread:

http://www.e90post.com/forums/showth...=364359&page=2
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