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High Pitch 10KHz noise on stereo. Think its the ETC.


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After much research and talking with a dealer, its seems that the Electronic Throttle (all models since 2007) may use 10 KHz to do PWM to control the throttle motor/position. This noise is getting injected into the stereo system (not sure how yet) but some boats are worse than others. My luck..... I think the noise is radiating across the whole boat, but am going to prove this tomorrow by connecting my whole stereo to an isolated battery. If the noise is still there then I know it is radiated and not conducted noise.

This only happens when the boat is on (of course) and at low stereo volumes and amp gains set normal. It gets worse when the amps are set to high gain. So setting the amps gain to a minimum will mask the issue. Maybe that's why Malibu is shipping boats out with amps at very low gains.

I remember hearing this same tone on some other Malibu's when I was test driving and just thought it was a bad stereo install. After a complete re-haul of everything no improvement.

Next time you guys are out on your 2007 or newer boat with ETC, can you turn your gains on amps up to midway and then listen to your stereo at very low volume (like a few clicks from lowest setting) and let me know if you also hear the 10 KHz tone? This noise is driving me nuts. It should happen in neutral and at very slow speeds. As once you go above 5 mph, its hard to hear over the engine noise.

I have read application notes that tell the ETC companies to use non audible frequencies for the PWM to drive the H-bridge chips which control the motor. So it should have been above 20 KHz and not 10 KHz. I am going to get the part number of the system and see if I can confirm the frequency used.

I think the solution is to put a filter right at the Throttle control near motor.

In the meantime, you can connect your iphone directly to the amp and the 10KHz tone goes away. Although if you have the iphone at minimum volume (so you can't hear song) and amp gains at maximum I can barely start to hear small 10KHz tone and other noise but this was just a test and not practical. This just hints that the noise is getting injected into head-end unit and not into the amps.

Edited by JoeMama
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I HAVE THIS SOUND!!!! Hopefully you can find a solution because it is also driving me nuts. My gains are turned down pretty low, but the noise is still there. I have a full Exile system and it didn't change after the factory stuff was removed. It still drives my stereo guy nuts, he tried everything to get rid of it a year ago and this may be the reason.

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  • 3 weeks later...

Well after about 70 hours of debug and work I got rid of the Stereo noise which originates from ETC motor 10KHz throttle noise. Malibu and Indmar should have chosen a better solution which should be based on inaudible 20KHz PWM or greater to drive the throttle motor. BAD CHOICE ON THEIR PART !!! Using a spectrum analyzer app on my iphone was the savior as I did not have an oscilloscope/spectrum analyzer. The throttle motor control is based on 10KHz and the rise/fall time of the 10 KHz is in the hundreds (or more) of MHz. Which means every 10 KHz there's 100plus MHz of noise getting radiated thru-out the whole boat and every wire can be picking this noise up. This noise turns back into 10 KHz from the antenna action of the RCAs, head init, and head unit ground. Those are the three variables. So need RCAs as short as possible, not much can do about the head unit, and then have very short ground/pwer from head unit to amp. And away from batteries. Easy way to see the signal is to take a 12ft RCA and connect to amp and have other end disconnected. Power the amp up and put iphone spectrum anaylzer next to speaker. In my case I get very loud 10 KHz tone at about 50dB. Using a 3 ft RCA cable picks up less noise.

My solution was re-locating all the amps (previously right next to batteries) from the port side and over to the starboard side about 3 ft from the stereo head unit. This is where it should be in the first place. I re-ran all the speaker wires and made RCA and power/GND twisted pair. Also removed a lot of un-neccessary audio routing. Saw very long wires (like 6ft) to connect devices that were 2 inches away. Unplugged my satellite radio which I never used. And disconnected the analog audio jack and selector port. Since I use bluetooth and USB from Iphone to radio.

I reduced my 10KHz tone by about 20dB and cannot even hear it now. This was an insane experience.

Now I need to worry about whether I will get condensation on my amps as they are not protected as was the case on the port side. So I think I may make an insulated re-movable wall around my subwoofer. Not sure yet as my amps are already marine grade.

Another option was to add snap on ferrites on the RCAs but I bought some from electronics store and they did nothing. But they also did not spec the device. So I am actually going to buy some 1MHz, 50 MHz, 100 MHz, etc snap ons just to see if I could have reduced the noise and not have had to re-locate the amps.

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please keep us updated about the ferrites. I really can't relocate the amps, so something needs to be done without doing that. thanks!!!!

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