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  #31  
Old 05-21-2013, 12:12 PM
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Typically, induced noise will be found on power cables that are connected to A) an old battery that no longer filters as well as it once did, B) power cables that are under-sized and conducting more current than they're suited for, C) cables that are conducting extremely high current (the magnetic field created by the current in a conductor is larger when current is high) or D), it may be from something as simple as a corroded connection that should be providing a path to ground for some device that would normally shunt noise, but can't.

In any case, the vast majority of stereo system noise problems come from incorrect wiring and bad grounds. Also, for those who have read or heard about 'star grounding', this is an electrical characteristic, not necessarily a physical topology. In cars, the floor pan is often the largest single piece of sheet metal and would seem to be the best place to ground amplifiers and other items in a car but that piece of sheet metal is also providing the ground path for lights, relays, motors and sometimes, computers or sensors. For this reason, it must be seen as an electrical goal- to connect everything so that all of the equipments' grounds are at the same electrical potential, 'potential' meaning voltage (voltage is potential energy). If this goal is achieved, no measurable difference in potential exists, therefore, no voltage can be measured between two or more devices.

An easy test for ground loops- get a test light and disconnect the audio/control cables, then connect the test light to the ground terminals for the head unit and amp(s). If the light comes on, current is flowing between them and this needs to be corrected. Once the audio/control cables are re-connected, this current will be carried by the audio/control cables and noise results.

Best practice- all audio/video power and ground connections come from one source. They're not connected to any other circuitry and the signal carrying cabling isn't run close to, or parallel to any wires that conduct high current AC or DC. Also, amplifiers are located together, not far apart and the power/ground wires of each amp should, ideally, be the same length (easier to center the distribution blocks between the amps than use longer wires just to accommodate an arbitrary placement)
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  #32  
Old 05-21-2013, 12:14 PM
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Originally Posted by EarmarkMarine View Post
You can also leave the RCA cable plugged into the existing amplifier, unplug the RCA from the HU, and short the left to right RCA at the HU end with a female to female barrel.

David
Do you ever use shorting plugs at the amp(s)? I have some from when I sold home audio- Sony supplied them for the unused phono jacks on integrated amps/preamps that had two phon inputs, to decrease noise pickup. I used them as an additional test if I found noise on shorted cables, just to verify/eliminate the cables as the source.
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  #33  
Old 05-21-2013, 12:29 PM
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OMG my brain hurts JimN. Thanks for the knowledge.
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  #34  
Old 05-21-2013, 12:40 PM
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I think I hit every nail on the head with this install but this one. Easy fix. I'll try to locate a route under the floor for the HU power as you said. I'm going to opt out of the relay and just fix the problem as David suggested. Probably leave the rca's where they are.

I have all the amps run like you mentioned in your post. You can see the blocks and we made sure they were all the same length from that. But never thought about the source.
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  #35  
Old 05-21-2013, 12:46 PM
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Quote:
Originally Posted by JimN View Post
Do you ever use shorting plugs at the amp(s)? I have some from when I sold home audio- Sony supplied them for the unused phono jacks on integrated amps/preamps that had two phon inputs, to decrease noise pickup. I used them as an additional test if I found noise on shorted cables, just to verify/eliminate the cables as the source.
No, not normally. The input selector would normally take unused RCA inputs out of the circuit. But I guess the two phono inputs were not on a selector and internally paralleled. It makes great sense.
But we do use a shorting RCA jumper at the input of the amplifier to isolate, test and eliminate the amplifier as a source of noise. Then we move the jumper to the opposite end of the long RCA to eliminate the cable.

David
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  #36  
Old 05-21-2013, 01:08 PM
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OMG my brain hurts JimN. Thanks for the knowledge.
How do you think I feel? That's been rattling around in my head for years.
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  #37  
Old 05-29-2013, 03:53 PM
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Guys, may I join the discussion? I've got a serious noise and will check the wiring, thanks for all the information shared.

Regarding the HU (Clarion CMD5). A yellow one, called memory lead, should be connected directly to the battery. That means - if I understand right - that this cable should be connected to the power source of the amps which is then finally connected to the dual battery switch.
At the moment I don't know where it is connected to at the moment. But is it ok to connect it to the + of the amp? Would the power on function still work? Guess yes since the amps are switched on via the blue/white cable (but get the power over red +, where finally the HU yellow is connected too).

There is another red cable at the HU which is called "switched power lead" and which should be connected to accessory 12+. Is it ok to connect to that cable for example another device such as a digital radio.

Thank you for your help
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  #38  
Old 05-29-2013, 07:46 PM
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Quote:
Regarding the HU (Clarion CMD5). A yellow one, called memory lead, should be connected directly to the battery. That means - if I understand right - that this cable should be connected to the power source of the amps which is then finally connected to the dual battery switch.
At the moment I don't know where it is connected to at the moment. But is it ok to connect it to the + of the amp? Would the power on function still work? Guess yes since the amps are switched on via the blue/white cable (but get the power over red +, where finally the HU yellow is connected too).
Yes, it is absolutely ok to piggy-back the head-units yellow B+ and black GND to the amps power cabling lugs. This is a sure way to have all the gear sharing the same battery source. If your amp uses a set screw that directly contacts the cable, make sure you slide the head-unit wires under the amps cable and not the top. Cranking down on that large setscrew can damage the small head-unit wire. also, avoid the side of the amp cable as there will be little tension there.

Quote:
There is another red cable at the HU which is called "switched power lead" and which should be connected to accessory 12+. Is it ok to connect to that cable for example another device such as a digital radio.
This red wire is what tells the head-unit to power on, its just a 12v signal, not load carrying. its not in the signal path, so where it gets its 12v from is rarely an issue. Most boats come from the factory with it on the key switch. We typically relocate them to a dedicated rocker just for the purpose of turning head-unit on and off, rather then having it cycle every time the operator shuts the engine off. Im not sure I understand what it is you are looking to connect it to or connect to it though. I think you are asking if you could use that 12v switched rocker to power up another device? If so, yes, as long as the circuit can carry the additional load.
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  #39  
Old 05-31-2013, 03:38 PM
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Thank you for your help, I now connected the yellow one to the positive wire of the amp. What caused the noise (it clacked even when turning on the tower lights for example) was most likely a chinch connection which had contact with the case of the amp and probably as well an Y chinch connector of poor quality. I'll have to check out however next time the boat is on the water to be sure.

Cheers
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  #40  
Old 06-25-2013, 10:11 PM
jrogers760 jrogers760 is offline
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Thanks for the info guys. I also have noise issues. When I hit the power trim I hear load cracks in the speakers and then hear the motor lifting. After reading the post I am sure it is because not all my + cables go to the common on the battery switch which I plan to fix. In addition, I have a large + wire going from the common on the battery switch to the amp, and have a smaller + wire going from the common on the battery switch to a fused terminal block under the dash where my HU connects on both the yellow and red wire (red wire has an inline finger switch.) This fused terminal also feeds lights and various other items (not the power trim). From what I gather (option #1), I should remove the yellow wire from my fused terminal block and terminate it directly to the + wire feeding the amp??? In addition, the red wire does not need to be moved from the fused terminal block as it is just an on and off switch and does not carry a load???
Or (option #2), would it be better to take the + wire currently feeding the amp and use it to instead feed the fused terminal block (which feeds lights and various other item). Doing this would eliminate that 2nd smaller + wire I had feeding the fused terminal block. In addition, I would run a new wire from the fused terminal block to the amp, followed by the HU yellow connected at the amp, and would leave the red on the fused terminal block.
I assume option #1 is appropriate but need some feedback from the pro’s. Thank you!
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