Background noise

[jhiestand]

I just installed a polywire iPod connector in our boat so our iPod charges while we're using it. I also thought it'd be good to use one less boosted signal input since our iPod goes into an HSE RVC, then into a Clarion EQ. When I powered up the stereo w/out the iPod connected I noticed some background noise. ARgh.. , although I think the noise was there even w/out the new polywire powered connector.

I know grounds are typically the culprit when it comes to noise. I have 'house' battery that all my stereo items are directly connected to with the lone exception of the head unit. Both amps, the EQ, the HSE and now the Polywire are all directly connected to the battery's +/- terminals (I do need to change the Polywire to a switched source). My head unit is not, however. Pretty much the only thing I use the head unit for is the remote power on/off lead -- so it's pretty much a fancy power switch that turns on amps/EQ/volume control. Since it's not directly grounded to the house battery could it still be suspect as a source of noise? I do have RCA's going from it to the HSE but never switch it.

Anything else I should check? I guess the other thing is power leads should run at right angles or at least not in parallel to source lines, so I should check that also. Just wondered if I might be missing something??

[EarmarkMarine]

Background noise as kind of an ambient hiss (like listening to a constant, distant waterfall) is usually unrelated to ground or supply loops. Its a normal part of adding all signal processors. This could be further compounded by using the headphone out of an ipod rather than the bottom and true pre-level output. You have five gain stages with the ipod, source unit, HSE (which also has considerable gain as a line amp), the EQ (also a high voltage line amp) and amplifier(s). That is definitely a prescription for noise. If you have HLCDs on the tower with an extra 6 dB (four times power) or more of treble emphasis then these will ruthlessly reproduce any flaw and particularly hiss. The solution is proper gain setting according to unity gain from the first to last component in the signal path. Over-gaining does not necessarily promote additional power or output levels. It can be a delicate balance between managing the noise floor and dynamic range.

Now, if you have a foreign noise such as a click or whine that is unrelated to the tempo of the program material then this would likely be caused by a ground or supply loop, however, gain seting can also be a contributor. This type of noise is generated by the boat electronics and is induced via a loop.

The B+ and ground of all audio source electronics and amplifiers must reference the same battery source at any time.

An ipod adapter could introduce a supply/ground loop by circumventing the intended above ground isolation of the RCA shields. Avoid using the top headphone jack and use the bottom ipod port for audio. Temporarly disconnect the supply/charger cord to see if that makes a change in the noise level.


David

Earmark Marine

[jhiestand]

You're probably right about gain settings. I do have the foreign click/noise, though. When the ipod disk spins up when the ipod wakes (yes, i still use an ipod classic) you can hear it whirrr up through the speakers. Faint, but w/out music playing you can tell it's there. I never got that noise when it was connected through the headphone jack. I also would get the same "whirr" noise when the ipod was connected through the headphone jack, BUT it also was connected through its pre-level output to a cigarette lighter to charge it. Note, that the cigarette lighter is powered through all the dash electronics, as is my head unit, and they're not directly grounded to my house battery. Would that make a difference?

Thanks for the reply!

Joe

[EarmarkMarine]

Anytime you use a cigar lighter power supply there is an increased chance of a supply or ground loop. Try it on battery power only. Its possible for the MP3 player's audio shield ground to be common with the chassis/power supply while the Clarion uses 'above ground' shields which can constitute a noise conflict. You won't know until you try. If this makes a difference then an I-Simple IS-75 is probably a better way to supply/charge the ipod.


David
Earmark Marine

[jdrei]

It probably wouldn't hurt to ground the HU to your stereo circuit. I have everything set up similar to yours on my 2007 SANTE, except my HU is grounded both to the factory harness and to stereo circuit. Also, I ground the IS-75 and my clarion to my largest amp. My background noise is very minimal despite the gain stages as David describes. When I first installed the Clarion and IS-75 to house wiring, the alternator whine and background noise was terrible!

[TX-Foilhead]

I think you're just hearing the iPod working, I think that just happens. I run a very similar setup, but with the iPod directly to the HSE main side through a JL line driver for my volume control. That way I avoided the line driver in the HSE. If I switch to a my iPhone then it goes away, but I like the Classic because I can keep everything on it as a .wav file and still have room to spare. I only use the iPhone for satellite radio.

[jhiestand]

You may be right, TX-Foilhead. If volumes are up with no music being played I can hear the ipod hard drive spin up when it wakes up. It's definitely tolerable, but I'll probably do a little clean-up work to try and eliminate as much as I can. Probably would be a good idea to ground the HU to the stereo circuit, also.