Ground noise after amp install

[littleape]

So I installed an amp and now I'm getting a bad ground noise when the motor is running.

I used 4 AWG wires for both ground and power. They both run directly from the battery to under the console up front on the side of the boat with no other wires. The battery is located on this side of the boat so the wires do not cross any other wires.

The only contact with another ground/power is at the battery terminals themselves. My battery has two terminal types, one the regular clamp style and another set of screw-on ones where the amp is hooked up to along with some other small wires. I believe those are the bilge pump and blower. Pitch of the noise changes when blower is turned on.

Radio to amp use brand new RCA cable, amp and radio are right next to each other.

What can I try short of some in-line noise filter? Maybe move the amp wires to the clamp on terminals on the battery? Boat is at a remote location so it's not something I can quickly test.

Thanks

 

[mike_i]

I'm assuming all was good with the radio prior to installing the amp. Is there any chance that the noise was there before installing the amp but now the amplifier is simply amplifying the noise especially while listening to a AM radio station? Normally a ground noise is describing a noise associated with an AC circuit known as ground hum, usually 60 Hz. Is that what you're hearing or is it a higher pitch swirling sound that changes pitch as you rev the motor? Is there a ground lug on the case of the amp? Either way run a wire from the case of the amp to a chassis ground. Can you temporally connect the amp directly to another battery with very short leads and see what happens? That would help determine if something like the alternator is inducing the interference into the wires or if the amp has poor shielding and the interference is being induced directly into the amp. Sometimes you can eliminate induced interference by twisting the entire length of wires between the battery and amp wires. Can you temporally get longer RCA cables so you can get the radio away from the amp? If the amp and radio are next to each other the amp may be inducing the interference into the radio. As you said, you can buy or build a simple noise filter, but it would be better to find and eliminate the source of noise if you can.

 

[littleape]

Radio is brand new and there was no noise before the amp was put in.

I'm not sure if the noise is 60 Hz but the blower definitely changes the sound compared to when just when the engine is running with nothing else. Did not check if sound changes with RPM of the engine.

It's a bit of a pain but I guess I could drag another batter in there to see if it's still there when on its own battery. I'm suspecting it will not be there since there's no noise when the engine is off but there is noise if I switch the blower on. This must be something about the battery terminals being shared.

 

[dingbat]

Here is a good troubleshooting guide for you

https://www.crutchfield.com/S-vWgPP...car/noise_suppressors_installation_guide.html

 

[sam am I]

I'll bet it's a "ground loop"............Your wiring is fine from what you've described, it's just the design/s, their interactions and even a single point ground won't fix the issue/s due to the enviro and some restrictions. It can happen, it's just a crap shoot sometimes and ya can work efficiently around it. I didn't read the trouble shooting guide above BUT definitally read over it as it could also apply and my suggestion below might be redundant....If so, apologies .

As a test to confirm the loop, take like a cell phone (ipod, mp3 player, etc, anything battery powered) with some audio on it and use it's audio out jacks (ya might need an adapter) as the audio source. The cell phone, by default, is electrically isolated beings its battery powered.

If the noise/hum is gone with the cell phone, then install a ground loop isolator transformer in-between radio/head and the amp...It'll break the loop.

I've personally tested this one in the lab and run one myself FWIW, it has a very flat frequency response, I recommend it

 

[littleape]

I'm going to try a much much shorter, 1.5', set of RCA cables with better shielding. The current ones I have are like 10' long and looped next to the amp and head unit.

 

[littleape]

No luck with a super short 1.5' RCA cable. I was testing it with the blower motor running and as soon as RCA is connected between the radio and amp the noise kicks in. The only connection between the blower motor and the amp is at the battery terminals but doesn't the radio/amp connection mean it's the radio thats the source? Unless the amp is "off" when there's no connection detected.

 

[mike_i]

Is there a way you can post several seconds of audio of the noise, maybe a YouTube video? You said "I was testing it with the blower motor running and as soon as RCA is connected between the radio and amp the noise kicks in." That makes sense since you only hear the noise with the amp and radio connected. I'm wondering if the RCA cables are acting like an antenna and inducing the interference into the amp.Did you try the radio and amp powered by a separate battery? Can you try shielded RCA cables? Is the radio a standard AM/FM radio? If so is the interference on both AM and FM?

 

[dingbat]

No luck with a super short 1.5' RCA cable. I was testing it with the blower motor running and as soon as RCA is connected between the radio and amp the noise kicks in. The only connection between the blower motor and the amp is at the battery terminals but doesn't the radio/amp connection mean it's the radio thats the source?

Doubt it....you most likely have a grounding issue.

Are both components (amp and radio) using the same ground connection?
Are the chassis grounds of both components tied together?
What happens if you lift the ground connections off one unit or the other?

Do other on-board motors (alternator, trim motor, bilge pump, etc.) cause interference as well?

Best practice grounding explanation
http://www.valvewizard.co.uk/Grounding.pdf

 

[littleape]

Hmm shoot now that I think about it the radio itself is grounded through the build in wiring harness of the boat. I must have not noticed the noise, or it wasn't present, when it was just the radio powering speakers with no amp.

I might have to just live with this for the rest of the season. It's too much of a pain in the butt, and limited time, to try and correct it at the cottage. I will probably need to run a dedicated ground wire, for the radio itself, to the battery or maybe splice into the amp ground since it's literally a foot away from the radio.

 

[sam am I]

Moving the radio's ground to the amp's ground point could certainly help some due to creating a "single point ground" which is definitely best practice as it reduces loop currents ......Might just fix it, however, it could only "reduce" it and it still may be there and the amp's gain will still just inherently continue to increase it.......That's the amp job, increase whats coming in.........

As I stated above, sometimes single point grounds doesn't help too much due to the currents flowing to each device differs due to the nature of the device and differing currents through various resistances creates differing potentials at each of the devices (amp and radio) ground references ....... Or in short, loop current occur because one device ground is higher than the other.

Again and this only takes a second........Substitute a battery powered auto device (i-phone, mp3 player, etc) for the radio, this will break the loop. If it plays normal (no noise) with motor running and pumps on, it's a ground loop. Install a inline isolation transformer.

The amp is just doing what it's suppose to do, amplify HOWEVER, It's amplifying the noise being created by the loop as well and the audio and that's what your hearing.

 

[littleape]

Hmm will try that, I think I have a 1/8 to RCA cable at the cottage to test with the phone.

 

[mike_i]

littleape, any update?

 

[littleape]

OK so new season and I thought I would look into this again while I have the boat on the driveway.

I ran a dedicated ground wire from the battery to the head unit, the amp already has dedicated cables from the battery for both ground and power, and still the noise is there when blower is ON. Only way to remove the noise is to leave gain at zero on the amp and with that there's just not enough volume, totally defeats the purpose of the amp.

Head unit looks like the source, when I remove the RCA connectors it goes away but maybe the amp shuts off automatically when those are not hooked up not sure. Attached is a pic of the battery wiring, the two big wires going out to the right are the ground/power for the amp.

Anything else I can try short of ground loop isolators?

 

[littleape]

Screw it, don't think there's anything else I can do thats simple like adding a dedicated battery, ordered a ground loop isolator.

 

[mike_i]

I'll ask again, can you post several seconds of the noise?

 

[Grub54891]

I got rid of the noise on mine by disconnecting the amp, radio, and removed them from the boat. Nature makes better sound.

 

[sam am I]

It can also help if you drop the original "Ig switched 12V" that powers the head unit(see attached drawing)...... Breaking this switched ig source 12V at the head unit and use it now to run a relay that in turn creates a local "cleaner switched 12V" that uses a direct path from the batt's (the amp's direct 12V).

Done this many times in addition to or not even using ground loops iso's at all and have had successful results.......As I said, it can be a crap shoot depending on manu's component designs and enviro's, but there are work around's.

You also said the bilge pump is buzzing as well........Sometimes adding a say a 0.1ufd ceramic cap directly across the pump's motor's power terminals can help....These motors are usually cheap'ish that make ton of electrical noise when running.

Worst case.......Headphones are always your safest bet!

 

[littleape]

I'll ask again, can you post several seconds of the noise?

I tried 3 different sets of RCA cables.

 

[sam am I]

Was that the bilge pump being turned on and off with the engine running?