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<blockquote data-quote="ultm8z" data-source="post: 8879828" data-attributes="member: 691847">New member here with a question that&#039;s baffling me...I have a car with two amplifiers... one for the front speakers and one for the rear speakers.&nbsp;&nbsp; Power filters on everything (battery input, switched power input, head unit power, etc).&nbsp;&nbsp; Common ground point for everything right near the battery.&nbsp;&nbsp; Runs super clean.Recently I bought a bluetooth dongle that has RCA outputs.&nbsp; I got a set of Y-cables to allow the bluetooth dongle to plug into the front amplifier &quot;in parallel&quot; with the head unit.&nbsp;&nbsp; This resulted in a really bad alternator hum.&nbsp; I confirmed it&#039;s the alternator because not only does the noise vary with engine RPM, but when I unplug the alternator (effectively shutting it off), the noise goes away.&nbsp;&nbsp; The bluetooth dongle also gets its power off the filtered power circuit and it&#039;s ground also goes to the common ground point.&nbsp; So I&#039;&#039;m scracthing my head how a set of Y-cables can introduce alternator whine??&nbsp;&nbsp; BTW, If I move the bluetooth dongle and the Y-cables to the rear amp, I don&#039;t get the whine.&nbsp;&nbsp; So I&#039;m wondering if there&#039;s something wrong with the front amplifer that&#039;s making more susceptible to it?Another question too...&nbsp; In order to boost the output on the front speakers, I bought a line amp.&nbsp; It definitely did the trick.&nbsp;&nbsp; However, when I shut the car off, I get a loud pop out of the front speakers.&nbsp; Any advice here would be appreciated.I suppose my easiest solution would be to get a head unit that has bluetooth built in as well as a more powerful front amplifier.&nbsp; But trying to see if there&#039;s an inexpensive solution.</blockquote>

[QUOTE="ultm8z, post: 8879828, member: 691847"] New member here with a question that's baffling me... I have a car with two amplifiers... one for the front speakers and one for the rear speakers. Power filters on everything (battery input, switched power input, head unit power, etc). Common ground point for everything right near the battery. Runs super clean. Recently I bought a bluetooth dongle that has RCA outputs. I got a set of Y-cables to allow the bluetooth dongle to plug into the front amplifier "in parallel" with the head unit. This resulted in a really bad alternator hum. I confirmed it's the alternator because not only does the noise vary with engine RPM, but when I unplug the alternator (effectively shutting it off), the noise goes away. The bluetooth dongle also gets its power off the filtered power circuit and it's ground also goes to the common ground point. So I''m scracthing my head how a set of Y-cables can introduce alternator whine?? BTW, If I move the bluetooth dongle and the Y-cables to the rear amp, I don't get the whine. So I'm wondering if there's something wrong with the front amplifer that's making more susceptible to it? Another question too... In order to boost the output on the front speakers, I bought a line amp. It definitely did the trick. However, when I shut the car off, I get a loud pop out of the front speakers. Any advice here would be appreciated. I suppose my easiest solution would be to get a head unit that has bluetooth built in as well as a more powerful front amplifier. But trying to see if there's an inexpensive solution. [/QUOTE]

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