engine (alternator) noise in speakers....

[CliffA]

a couple weeks ago i added two new 6" x 9" JBL marine speakers in the cockpit of my boat just in front of the rear bench seat....they compliment the two 6" JBL speakers that were already installed in front of the captain's and passenger cockpit seats.....i also installed a Pyle marine 400W four channel amp behind the dash to power the 4 cockpit speakers....i use the stereo head unit to power two speakers in the cabin and two speakers on the transom.....i have wired in a selector switch to be able to select which speakers are active....i can select to play only the cabin speakers, only the cockpit speakers, or only the transom speakers or different combinations of speakers...

everything sounds great when the engine is not running...however when i start the engine i get engine (alternator) noise through the cockpit speakers only....the cabin speakers and transom speakers that are driven by the head unit sound fine...so this tells me i have a problem with the amp driven cockpit speakers.....

here are the details concerning the amp installation:

i used an 8 gauge power wire directly from the battery to the amp.....this is a fairly long run of approximately 20 ft......i used a smaller gauge wire (not sure what gauge) as the ground between the amp and the main ground bar behind the dash...the length of the ground wire is around 2 ft......i used 12 gauge speaker wire from the amp to the 4 cockpit speakers for the speakers + and - connections......i wired the 'remote start' terminal of the amp to a spare 'Accessory' rocker switch on the dash....so i can turn the 4 cockpit speakers on/off with this 'Accessory' switch by turning the power to the amp on/off.....i used triple shielded twisted RCA patch cables between the head unit pre-out terminals and the amp...the length of these patch cables is 3 ft.....i tried adjusting the 'gain' controls on the amp which helped some but did not remove the engine noise.....

i have done a little reserch on possible causes of the engine noise....here are the items that i know of i should check...

- do not route speaker wires too close to any power wires
- may need to increase the gauge of the ground wire to the same gauge (8 gauge) as the power wire and keep the length under 3 ft.
- do not route the RCA patch cables too close to a power wire

if anyone has any other suggestions on things to check they would be appreciated....

cliff

 

[scoflaw]

Had a similar issue although I ran a heavy gauge ground wire from the amp to the battery. The fix was I ran the head unit ground wire directly to the amp

 

[CliffA]

Had a similar issue although I ran a heavy gauge ground wire from the amp to the battery. The fix was I ran the head unit ground wire directly to the amp

ah, that sounds like a good idea...i had read that the head unit and amp should use the same ground source to avoid a ground loop problem....i thought that since both the amp and the head unit used the same ground bar that would be sufficient....but i like your idea better of grounding the head unit directly to the amp ground....

thanks..

cliff

 

[dvx216]

I'm confused way you think larger gauge wire will help? The size of the wire is for the current it will carry 8 gauge wire is good for around 40 amps unless you are grossly under sizing your wire length is not a concern .Your ground wire is just as important as your hot wire it is the return to the battery . Some thing like an amplifier with high amp draw should have direct feed going to it (+) and (-) check the amp draw and size accordingly. Just guessing but the ground bar behind the dash is not wired with that heavy of gauge wire plus all the things that are using this ground bar add up plus and this could be where the noise is coming from.

 

[OldSkool]

dvx to your point, I think the gauge of wire is not as important as running a separate circuit to the battery is. If you tap into an engine circuit you may pick up static electricity or magnetism from the coil or other electrical equipment. We see this a lot in my industry. Many 2 way radios are installed into the engine harness and the noise appears until the wires are removed and directly linked to the battery + and -.

 

[scoflaw]

[h=1]12 volt Wire Gauge vs. Amps[/h] 12 Volt Wiring Gauge Requirements at specific Amps for Automotive Electrical Systems ​ ​ ​ To choose an adequate wire gauge, determine the amp draw (amperage) that the wire circuit will carry. Then measure the distance that the wire will travel (length) including the length of the return to ground (the ground wire running to the chassis or back to a ground block or battery. Using these two numbers, Amps and length, locate the nearest gauge value in chart below. For 6 volt automotive systems typically a wire gauge 2 sizes larger than what is shown should be used. Amps @ 12 Volts LENGTH OF WIRE American Wire Gauge (AWG) 3' 5' 7' 10' 15' 20' 25' 0 to 1 18 18 18 18 18 18 18 1.5 18 18 18 18 18 18 18 2 18 18 18 18 18 18 18 3 18 18 18 18 18 18 18 4 18 18 18 18 18 18 18 5 18 18 18 18 18 18 18 6 18 18 18 18 18 18 16 7 18 18 18 18 18 18 16 8 18 18 18 18 18 16 16 10 18 18 18 18 16 16 14 11 18 18 18 18 16 16 14 12 18 18 18 18 16 16 14 15 18 18 18 18 14 14 12 18 18 18 16 16 14 14 12 20 18 18 16 16 14 12 10 22 18 18 16 14 12 12 10 24 18 18 16 14 12 12 10 30 18 16 14 12 10 10 10 36 16 14 14 12 10 10 10 40 16 14 12 12 10 10 8 50 16 14 12 10 10 10 8 100 12 12 10 10 6 6 4 150 10 10 8 8 4 4 2 200 10 8 8 6 4 4 2 ​ Also see: Automotive Wiring Tips - Using Relays 12 Volt Wiring Gauge Requirements at specific Amps for Automotive Electrical Systems 12 Volt Wiring - Distance and Amps to Gauge Chart Converting Candlepower to Watts and vice-versa & Other Offroad Light Information Automotive Wiring Tips & TechniquesHEI Ignition Installation and Review Using LED lights in your Vehicle LightForce Driving Lights Install/ReviewWhat are HID Lights? ​ ​

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[CliffA]

Thanks for the input guys.....I bought 20' of 8 gauge wire for the amp ground yesterday to connect directly to the battery....This is a small amp that only pulls 15 amps at max volume.....8 gauge is probably overkill for this application but that's OK....also plan to run the head unit ground to the amp ground.....this way both the head unit and the amp will have the same dedicated ground directly to the battery.....I hope to get to the boat this afternoon to work on this.....but the forecast is for 80% chance for T'storms this afternoon.....

cliff

 

[CliffA]

Problem solved....I installed a dedicated 8 gauge ground wire directly from the amp ground terminal to the battery negative terminal but that did not work....in fact that made the noise worse.....i left the new 8 gauge ground wire in place and connected the ground wire from the head unit to the amp ground terminal and that solved the problem.....

cliff

 

[Steve Craig]

Alternator noise in the radio/sound system is an indication the diodes internal to the alternator are failing/gone.
Do you have internal or external voltage regulator ?
There may be more than one location but you will need to confirm with a wiring diagram.

 

[CliffA]

Alternator noise in the radio/sound system is an indication the diodes internal to the alternator are failing/gone.
Do you have internal or external voltage regulator ?
There may be more than one location but you will need to confirm with a wiring diagram.

well dang Steve.....i was feeling all good about this repair until now.....

there was/is no noise from the 4 speakers that are driven by the internal amp in the head unit.....the only time i got the noise is AFTER i added a small 400W amp to power 4 other speakers in the cockpit......from my research i was thinking the noise came from a 'ground loop' problem created by not having the two components (amp and head unit) grounded to the same point.....once i corrected that the noise went away....

i am 99% sure the voltage regulator on my engine is internal to the alternator......the voltometer on the dash always seems to read correctly.... with a fully charged battery the meter reads around 14.5V.....

does all this still sound like i may have a problem with these 'diodes' you speak of?.....electronics is not my strong suite but i know the basics and i am always willing to learn.....

cliff

 

[Steve Craig]

Just sold it but you would be surprised what you learn keeping a 43 year old Buick on the road. It was externally regulated with diodes/capacitors in 5 locations from factory !
Boats don't have a parking brake so there's one place we don't have to look!
Guessing that by '98 everything was internally regulated. Easy job to do on the bench once the boat is pulled for the season. Easier yet to replace the alt. in the Spring before you splash it !
Get a DC volt meter across the battery terminals to verify the battery charge condition. Do not put all your faith in the dash mounted unit.
I just changed mine out as the existing was showing well above 16V while running at about 2500 RPM. My Fluke meter confirmed 13.8V, proving it was the dash mounted unit.