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Thread: Moto G7 Optimo Maxx - Noise from headphone jack

  1. #1
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    Moto G7 Optimo Maxx - Noise from headphone jack

    Hey guys;
    I have a Moto G7 Optimo Maxx (Tracfone), which I sometimes connect to my sound system when listening to other sources with headphones. I use a Behringer UMC202HD USB audio interface. The phone is plugged into the Line-In sockets on the AI via a pair of transformers to the XLR connectors. The transformers, which convert a 1/4in phone jack to a XLR plug act as isolation transformers to eliminate ground loop related noise.

    That works fine, but when the phone is connected and there is nothing playing on the phone, I hear a low level buzzing sort of sound. I have traced it to the phone, and it is only present when the phone is not playing any sound.
    If I am playing music, or an audiobook on the phone, then hit pause, there will be a period of about 1 second where there is no noise, then there is the buzzing.

    I believe that what is happening is the phone is putting the output amplifiers of the headphone jack into a high-impedance state to conserve battery.
    Having a high impedance line connected to the AI input is prone to picking up noises. Even when that line is not plugged into the phone, and just hanging in mid-air, it picks up some noise.

    One might ask: Why do you keep the phone connected and/or the line inputs of the AI turned on when you're not listening to anything on that line?
    To answer this question: I like to watch movies and other media on my Windows PC, and have my headphones connected to the Behringer AI. At the same time, I don't want to miss a phone call or text, thus I leave the phone connected.
    I have been thinking of going wireless, but I would need a pair of cans that have advanced multipoint capability, and these are not so easy to find, and can be quite expensive.

    As a fix for the problem, I have been considering building a simple circuit that would monitor the line from the phone to the AI, disconnecting and grounding the inputs to the AI when the sound level on the phone is below some level that is well below anything I want to hear. There would of course need to be a time delay before the circuit would disconnect the inputs.

    Perhaps all of this is overkill, but I thought it might be an interesting project.
    I have looked through all of the menus on my phone to see if there is an option to stop the phone from turning off the headphone output when nothing is playing, but so far I have not found anything.
    This is the reason for this post: I want to make sure I have exhausted all software options before building a hardware solution.

    Any thoughts on this?
    Thanks
    Ultrarunner2015

  2. #2
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    Quote Originally Posted by ultrarunner2015 View Post
    Hey guys;
    I have a Moto G7 Optimo Maxx (Tracfone), which I sometimes connect to my sound system when listening to other sources with headphones. I use a Behringer UMC202HD USB audio interface. The phone is plugged into the Line-In sockets on the AI via a pair of transformers to the XLR connectors. The transformers, which convert a 1/4in phone jack to a XLR plug act as isolation transformers to eliminate ground loop related noise.

    That works fine, but when the phone is connected and there is nothing playing on the phone, I hear a low level buzzing sort of sound. I have traced it to the phone, and it is only present when the phone is not playing any sound.
    If I am playing music, or an audiobook on the phone, then hit pause, there will be a period of about 1 second where there is no noise, then there is the buzzing.

    I believe that what is happening is the phone is putting the output amplifiers of the headphone jack into a high-impedance state to conserve battery.
    Having a high impedance line connected to the AI input is prone to picking up noises. Even when that line is not plugged into the phone, and just hanging in mid-air, it picks up some noise.

    One might ask: Why do you keep the phone connected and/or the line inputs of the AI turned on when you're not listening to anything on that line?
    To answer this question: I like to watch movies and other media on my Windows PC, and have my headphones connected to the Behringer AI. At the same time, I don't want to miss a phone call or text, thus I leave the phone connected.
    I have been thinking of going wireless, but I would need a pair of cans that have advanced multipoint capability, and these are not so easy to find, and can be quite expensive.

    As a fix for the problem, I have been considering building a simple circuit that would monitor the line from the phone to the AI, disconnecting and grounding the inputs to the AI when the sound level on the phone is below some level that is well below anything I want to hear. There would of course need to be a time delay before the circuit would disconnect the inputs.

    Perhaps all of this is overkill, but I thought it might be an interesting project.
    I have looked through all of the menus on my phone to see if there is an option to stop the phone from turning off the headphone output when nothing is playing, but so far I have not found anything.
    This is the reason for this post: I want to make sure I have exhausted all software options before building a hardware solution.

    Any thoughts on this?
    Thanks
    Ultrarunner2015
    Because your external audiodevice not suitable to use such application.
    When input is low (silence) your audio system AGC automatically increase power so you hear noice when phone play in silence.

    Sent from my LG-LS997 using Tapatalk

  3. #3
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    I have the same noise issue when I connect the phone to my car stereo using the headphone jack.

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    Nothing I can do about the AGC in the Behringer. There is no adjustment.
    Building a circuit to cut off the input when the level is very low is probably not the best method to handle the problem.
    If I could get a schematic of the Behringer, I might have a chance at hacking it, but even with the schematic, I don't have the SMT soldering equipment that would be required.
    Perhaps a better AI? I wonder whether the Focusrite models have a different way of handling such noise, but I honestly doubt it.

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    I have found an acceptable method to mitigate the noise from the phone.
    I turned down the volume controls for the line input on the AI, and turned up the volume level on the phone.
    Since the noise I was hearing from the phone is unaffected by the phone's volume setting, I have reduced the noise to an acceptable level.
    If I really want to enjoy noise-free music from my headphones, I will simply hit the switch on the AI which disconnects the direct input from the line inputs to the output amp. I won't hear anything from the phone, but when I want uninterrupted music in my ears, I don't want the phone to distract me anyway.

    Digital Rules;
    You might want to try the same thing in your car. That said, I find that when I connect my phone to the aux input on the Pioneer receiver in my Subaru, I need to crank the receiver's volume way up to compensate for the low level output from the phone. I haven't noticed any noise, but then, external road noise will easily cover up the noise if there is any.
    The real issue in the car is that, if I forget to turn the volume control on the receiver down after using the phone, then I switch to radio, I get a jolt of extremely loud sound from the speakers.
    I had thought of using an amplifier between the phone and the receiver, but it wasn't worth the cost of a good preamp, and I never really considered it a problem.

  6. #6
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    Exactly, running the phone at max volume does reduce the noise floor.

    The Pioneer head unit is 15+ years old and still sounds incredibly good. Hard to find new head units with parametric equalizers, so not gonna replace it till it dies .

    Sent from my Moto E (4) Plus using HoFo mobile app

  7. #7
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    My Pioneer is at least that old. I installed is shortly after buying my Subaru Forester XT in 2004. I wanted to connect my iPod to my car's sound system, and the 'premium' sound system that came with the vehicle didn't have an aux input, so I tried one of those nano-powered FM transmitters. I wasn't at all happy with the results, so I installed the Pioneer. It has a single CD slot, and yes - a cassette tape slot as well.

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