Looking for a 12 Volt Noise Supressor

[Bruce]

My refrigerator has induced noise into the stereo when it is set to a high volume but does not have input. I often do this to control the volume from my phone which is playing music while we are on shore. I see several products available but do not see any that are marine rated.

@David Analog, do you have a suggestion?

 

[Bob27]

I would suggest an inline noise filter for the HU power wire - available at a car audio shop. They look like a plastic case over the wire. Essentially it is an inline coil of wire (inductor). I have used ones that looked like a small transformer with only 2 wires that worked excellent. Hope this helps. Cam.

 

[David Analog]

My refrigerator has induced noise into the stereo when it is set to a high volume but does not have input. I often do this to control the volume from my phone which is playing music while we are on shore. I see several products available but do not see any that are marine rated.

@David Analog, do you have a suggestion?

Contemporary source units usually have very good filters for the voltage supply. In the end, you may be better served by filtering the fridge.
Before purchasing noise filters I would first determine exactly where and how the noise is entering the signal path.
No use of an inverter, correct?
Does the fridge noise change pitch when you rev up and down the temperature control? (just kidding)
I'm not very clear on the input source. Could you go into a little more detail.

 

[Bruce]

@David Analog, the refrigerator is a 12 volt unit with a small 12 volt compressor.

I am picking up power for it at the switched side of a blue seas LVD which is also where the house circuit that powers the stereo picks up.

The head unit is a Fusion IP600. I do not have any external amplifier.

The noise comes through the speakers when the volume is at or near max and nothing is playing. The input selected is a Fusion BT100 Bluetooth module. The BT100 is powered separately and connects via RCAs. It is possible that the noise is coming in via the BT100 which certainly has a lesser power supply. I would want to condition the power to both.

The noise heard sounds like the compressor operating but it is coming out of the speakers. It is almost like I used a microphone to amplify the compressor sound. It is at a low level and would never be noticed with music playing but it is noticeable when we turn the music off and leave the volume up.

How would I filter the fridge? It is a typically 1 amp load with peaks around 5.

 

[David Analog]

Try this. Disconnect the Bluetooth module and take one half of a very short RCA cable and jumper the HU left and right input together (in other words, shorted). If you have zero noise with the volume turned up then try an RCA ground loop isolator between the Bluetooth module output and the head unit input.

 

[Bruce]

@David Analog, do you recommend any brand or model of RCA ground loop isolator? Googleing most of what I see is off branded in the $10 to $20 range.

Thank you!

 

[David Analog]

@David Analog, do you recommend any brand or model of RCA ground loop isolator? Googleing most of what I see is off branded in the $10 to $20 range.

Thank you!

I'm not sure which are the good or bad brands. I do know there are different qualities where some have an impact on the bandwidth while others do not. PAC is well known.

 

[farrelltravis]

What about a cheap ferrite bead?

http://en.wikipedia.org/wiki/Ferrite_bead

 

[David Analog]

What about a cheap ferrite bead?

http://en.wikipedia.org/wiki/Ferrite_bead

They work for certain applications. I've used then often. But if the test proves that the noise is caused by a ground loop which sends DC traveling down the outer audio cable shield and inducing any noise that is modulating the DC into the signal path, I'm not sure it will work. A ground loop isolator interrupts and impedes the flow of DC while a choke/inductor will not. That's why I suggested testing first to find the method and point of noise inducement before selecting a specific filter type. At this time I only suspect that the Bluetooth module and HU have their own independent power supplies/sources and that the audio shield connection between the two must be broken.

 

[farrelltravis]

@David Analog you would enjoy ham radio. No question.

 

[David Analog]

Btw, I have used the clamp-on ferrite chokes on marine VHF radio antenna coax cables to keep the auto pilot from veering off in another direction when you key the mic.

 

[Bruce]

I ordered a noise suppressor from Amazon that had excellent reviews and claimed to boost the output level. It worked to block the noise but unfortunately reduced the signal level many decibels.

The USB sound card that I am using with the Raspberry Pi to play audio has a Toslink optical output. In September I ordered a Digital Toslink to Analog adapter that came with a USB power cable and a Tosllink cable for $9. I finally got around to connecting it today. The output level from the adapter is equivalent or higher than that from the sound card. So this may be the perfect solution for my noise issue.

Now that Pi is working correctly I will writeup the complete system which stores music and allows anyone on or near the boat to choose music and control volume from their phone.

I had a number of threads when I was looking to suppress the noise so I am updating all of them.

The UPC of the unbranded Toslink Adapter that I am using is 713665000703.