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Old 10-19-2013, 09:32 AM
djue djue is offline
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Stereo System high pitch hum

I have a 2012 X30 with CMD6 clarion source unit and 3 JL amps. The system has always had a small high pitch hum that does not vary with RPMs. When I added a Wetsounds 420 SQ, the hum amplified. After hours of trouble shooting (grounds to one point, all B+ from the house battery pole on the battery selector, Rca wire isolation) I finally found that when I disconnect the clarion remote 8 pin DIN wire from the BIG computer, all noise disappears. Any ideas on how to get rid of this type of interference? Now, I just use my Wetsounds for volume control and have the unit disconnected from the BIG system.

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Donnie Jue
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Old 10-19-2013, 08:11 PM
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David Analog David Analog is offline
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You have taken the correct path thus far in your trouble shooting.
All the audio electronics should be wired to the 'Common' battery post (and not the battery bank post if that post is battery direct) if it is a conventional dual battery switch. If the computer is accessing power from a different battery bank then you have introduced a supply loop that is typically noise inducing. If the computer induces noise then the computer needs to access the the identical B+ point and the identical ground point as 100% of the audio gear including the source gear (HU & EQ). You can canabalize and standard RCA ground loop isolator for one of the small EI transformers contained inside. The transformer can be used to break the DC connection on either the DIN cable shield ground, another internal DIN cable ground wire or both.
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Old 10-19-2013, 08:26 PM
djue djue is offline
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Thanks for the info! I'll confirm but I believe all B+ originate from the blue seas dual battery switch common. I also use Bosch style relays for ignition and remote circuits.
My stereo grounds go straight to one of the batteries. The Mastercraft BIG computer is grounded to a grounding bar near the engine. Could be a problem?
Do you now which pin on the clarion DIN remote is ground?

Thanks Again
Donnie Jue
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Old 10-19-2013, 08:44 PM
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David Analog David Analog is offline
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When it comes to Blue Sea, make sure you are making a distinction between a conventional dual battery switch and dual circuit battery switch. There's a big difference in application and Blue Sea makes both.
Tough to beat a ground close to the engine block grounded at the engine block (the largest metal mass on the boat). But if there is any resistance between this point and the battery ground point then you have a voltage differential and therefore a potential noise conflict.
I don't know what the ground pin is but the outer shield is a breeze to identify once you snap the DIN plug end apart. Clarion technical should be able to give you a pin diagram. The ground pin is easy enough to identify with a basic multimeter.
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Old 10-19-2013, 09:01 PM
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I would look at where the cabling is routed for the stereo. If it's bundled with other boat wires, it's possible that proximity is causing the problem. If it's possible to remove the remote's cable from where it's running and change the location, it's possible that moving it is the only thing needed to cure the noise problem.
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Old 10-19-2013, 09:03 PM
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Quote:
Originally Posted by David Analog View Post
You have taken the correct path thus far in your trouble shooting.
All the audio electronics should be wired to the 'Common' battery post (and not the battery bank post if that post is battery direct) if it is a conventional dual battery switch. If the computer is accessing power from a different battery bank then you have introduced a supply loop that is typically noise inducing. If the computer induces noise then the computer needs to access the the identical B+ point and the identical ground point as 100% of the audio gear including the source gear (HU & EQ). You can canabalize and standard RCA ground loop isolator for one of the small EI transformers contained inside. The transformer can be used to break the DC connection on either the DIN cable shield ground, another internal DIN cable ground wire or both.
So, you want him to make the shield useless by inserting an isolation transformer in-line?
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Old 10-19-2013, 09:42 PM
djue djue is offline
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Great ideas!! I have an extra clarion remote cable. I'll run it temporarily away from all wiring and see what happens. I'll confirm my blue seas B+ common. If no luck, I'll run my stereo ground to the ground location near the engine with the BIG computer. Last resort, I'll try the remote wire ground loop isolator - if I can figure out how.

Donnie Jue
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Old 10-20-2013, 11:32 AM
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David Analog David Analog is offline
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Quote:
Originally Posted by JimN View Post
So, you want him to make the shield useless by inserting an isolation transformer in-line?
Can't answer a poorly constructed question.
But use the transformer? Absolutely, as a test at minimum.
The shielding function will still be intact just as it is with a standard RCA ground loop isolator. It simply keeps DC (that may be modulated, ie; noise) from passing down the shield from one device to another.
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Old 10-20-2013, 12:46 PM
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Quote:
Originally Posted by David Analog View Post
Can't answer a poorly constructed question.
But use the transformer? Absolutely, as a test at minimum.
The shielding function will still be intact just as it is with a standard RCA ground loop isolator. It simply keeps DC (that may be modulated, ie; noise) from passing down the shield from one device to another.
Beside cost, if this is a better way to shield, why don't the manufacturers break the shield and use a small value cap, in series? It would still act as an AC/RF shield, but there would be no DC connection (unless they're using the shield as THE ground).

I don't remember the last time I heard of a shield that was acting to cause this kind of problem when the cabling was routed correctly (away from major noise sources).
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Old 10-20-2013, 07:39 PM
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David Analog David Analog is offline
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Quote:
Originally Posted by JimN View Post
Beside cost, if this is a better way to shield, why don't the manufacturers break the shield and use a small value cap, in series? It would still act as an AC/RF shield, but there would be no DC connection (unless they're using the shield as THE ground).

I don't remember the last time I heard of a shield that was acting to cause this kind of problem when the cabling was routed correctly (away from major noise sources).
That's a good question. I suspect that it has something to do with capacitors normally being used in parallel as an electrical shunt to send any AC noise component to ground rather than in series applications. Also, the capacitor may not function in series and still allow the full shielding function not to mention there may be a problem with it not being linear, interrupting the DC, but still passing the AC components.

In noise issues, rarely do I see cabling that is adequately shielded being a proximity issue related to other wiring with a fluxuating magnetic field. Most often it is a potential difference causing the DC current to find a path to circumvent the isolation. When the lowest resistance path happens to be a connecting ground shield or other wire between two items in the signal path, then you have DC present on that line. And that DC current always carries the AC ripple that is there in every car or boat, whether from the alternator, management module, or a power supply.

Auxilary inputs can be a common noise problem when using a separate ipod or phone power supply (plugs into cigar lighter, etc.). Again, this is a conflict in the ground potential causing the flow of DC current down the shield that was intended to protect the center conductors carrying the audio signal from induced noise. But now it is actually acting as the noise transmitter. Kind of like the fox protecting the hen house. The noise usually disappears once you go to the ipod battery power and end the conflict in ground potential. Or, a ground loop isolator (using small isolation transformers on the ground shield) normally does the trick.

I'm not a fan of using a ground loop isolator as a bandaid while the core problem is left intact. But there are just a few instances when it is the best solution.
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