Noise from newly installed ext VHF speaker

[boatrboy]

I added a small external VHF speaker. It is wired to the two wires which came on the OEM radio labeled "external speaker".

It works fine, BUT, with the refridge on, in DC mode only, I get a noise/humm thru this speaker. With shore power hooked up and the refridge on in AC mode (DC switch in off position) , NO noise. :smt017 :smt017 .

I have run the speaker wire thru a hole in the helm where my GPS antenna wire and power connection come thru and I have wire tied the wire with these wires direct from the back of the VHF. The speaker wire is separate from all other power lines. I did verify that the GPS is not the culprit by turning it off when checking for the humm.

Any input would be greatly appreciated as this humm drives me nuts!

 

[Dave M.]

So the noise is apparently caused by the fridge, and it is getting into the VHF speaker. First thing to find out is whether it is getting into the VHF itself and coming out the speaker lead, or is it just getting induced into the speaker leads themselves.

It if is coming into the VHF radio, say through the +12V and ground, then the humming should go away when you turn off the radio. Also, the amount of hum would probably be dependent on the radio volume.

If it is just coming into the speaker leads, then it should sound the same whether VHF is turned on or not. If this is the case, then re-routing of the speaker leads should solve the problem.

I assume that it does it only when the fridge motor is actually running. Is that correct, or does it do it even when the fridge is cycled off?

 

[boatrboy]

Dave,

The noise will stop when the VHF is off. It is weird that the DC part of the Refridge causes this kind of noise and why does it only happen now that I installed an external speaker?

To answer your question about the compressor running or not, I am not sure if the compressor kicks off if the noise stops. I will check that Sunday.

BTW - do you think that speaker polarity could cause this? The speaker did not say which wire was pos or neg, however, one wire did have a white stripe. I think the radio had a green and yellow wire?

 

[Dave M.]

There are a couple of possibilities I can think of on why now with an external speaker. One is that your installation may be picking up higher frequency noise from the compressor via the power leads. It then gets picked up via the speaker leads, then fed back into the amp and get detected and lowered in frequency to be audible. I doubt this is the problem, though. You could verify it is not by connected the external speaker close to the output of the VHF to verify that does not change things.

The other is that the radio may have a separate amp built in to drive the external speaker, and that amp may have a failed filter cap that keeps power supply (+12V) noise out of the external speaker amp.

Normally a battery is a very good capacitor, and makes a good filter to get rid of noise generated by loads such as the fridge compressor. But if you run long leads off the battery, to the helm for example, and then connect on a noisy device and one that is sensitive to noise, the long leads will prevent the battery from doing the filtering of the noise. So it will get not be filtered nearly as well. Then interference from one device to another is more likely, and if the device being getting noise on the battery leads has defective filtering, then noise is the result.

I doubt that speaker polarity has anything to do with it.

I don't know how the fridge compressor works, so I don't know what noise it might generate.

 

[Sea Ray 300]

Just adding a small thought, if re-routing and shortening the wire doesn't work.

Many times wiring in particular applications are "shielded", so as not to pick up "noise" from other components.
A "shielded" wire is nothing more complicated than the two conductors being encased in a braided wire, or foil, which is then grounded. Similar in concept to the cable TV wire at home, or the one from a boat TV antenna, but they only have one conductor.
This may be a solution in your case.

Assuming that your speaker and radio are made by the same company, and therefor compatible, I would recommend that you contact the radio manufacturer, and ask about this as a possible solution, if they determine that the radio or speaker is not faulty.

Also, if it is a solution, make sure the new wire is of marine grade.

 

[Cocktail Time]

Not sure if this is a fix or not, but two things come to mind:

1) Is the DC switch for the fridge connected to the same ground bus as your VHF? IE-Your VHF should be wired directly to a constant 12v power source and a direct ground just like a bilge pump so if you had a short in the system your VHF would still operate for safety. If it is you could ground the VHF directly to the battery or a different ground bus and that should fix your problem.

2) If there is no way around directly wiring the VHF power suppy and ground try a 12v inline Noise Filter like this, http://cgi.ebay.com/10AMP-NOISE-FIL...31QQihZ007QQcategoryZ1502QQrdZ1QQcmdZViewItem
They also available at Radio Shack should be under $20, they also work well in removing high frequency noise from hi-output alternators as well in both your 12v stereo and VHF.

Hope this helps...

Dan

 

[SearayPaul]

Dan:

Thank you for posting that. I have been trying to remember what the part was called for a couple of days. I kept calling it an RF choke but I new that was not right and did not want to post bad information. Thanks for refreshing my OLD mind.

 

[brimanst]

I agree with looking at the grounds first and make sure that each device has sufficient separate grounds to the bus. Also, you may be able to just twist your spealer wires to stop the unduction of current into the circuit. If you lay wires next to each other for a long distance you can get cross-talk. Try to "unzip' the wires, or go get some pre-twisted wires if you have to use the same run. Hope this helps.

briman

 

[boatrboy]

More details - The factory wiring is intakt nicely and there are two ground bus-bars attached to the port side under the dash. These are connected to each other by a factory installed black lead (large size approx 10 ga) Everything under the dash appears to be attached to this points.

I did try to move the speaker wires to no avail. Now I will admit I forgot my wire ties so I did not really cut and re-route, but I was able to move the wires quite a bit, but the noise never changed one bit.

The noise only comes on when the compressor (DC) kicks on. While I was wiggling the wires I got excited as the noise stopped, but as soon as I heard the compressor kick on, I realized I was fooled.

I found the positive lead from the VHF and it goes directly into a circuit breaker labeled accessory. I guess my next step will be to try the noise suppressor at radio shack.

Also - the radio is the stock Raymarine (I think) and the speaker is just a no brand small VHF speaker purchased at Boaters World for $14.

Thanks everyone and I will update after I install the filter.

 

[boatrboy]

I can't seem to edit so I meant to say "starboard side" not "port side".

 

[boatrboy]

2) If there is no way around directly wiring the VHF power suppy and ground try a 12v inline Noise Filter ........

They also available at Radio Shack should be under $20, they also work well in removing high frequency noise from hi-output alternators as well in both your 12v stereo and VHF.

Dan - You hit the nail on the head. I could not find a Radio shack that had a filter, but, the local Pep Boys had one in the radio section for eliminating engine related noise in car stereos for !0 bucks. I untied the speakers wires first and tried re-routing and twisting, but no luck so when all was said and done, I installed the filter and no more refridge noise. :smt038 :smt038 :thumbsup:

Thank you all for the help!

Mark

 

[Cocktail Time]

Mark,

Glad I could help! I might be new to this forum, but what a great use of the internet!
We've all had instances where we've paid for someone to fix something and later said "I could have done that for a whole helluva lot less" or had something go wrong that was easy enough to fix but nobody around to tell you what to do.

There seems to be some people on this website that have forgotten more than I will ever know about boats and Sea Rays in particular. That merits a CSR burgee by itself...

If we all share our knowledge about what not to do, and more important, what we would do if we had the chance to do it all over again, what a great source of information this site is and could be.

Long response, but I love to help, hope I don't come across like a dumbass or a know it all, cause hopefully I'm neither.

Dan