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Hacked Google home mini to have a line out - weird ground noise issue when no sound.
Hacked Google home mini to have a line out - weird ground noise issue when no sound.
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Old 10th October 2020, 07:44 PM   #1
bakeri is offline bakeri
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Default Hacked Google home mini to have a line out - weird ground noise issue when no sound.

Hi All,


This is actually my second thread on this. My original one was in Class D, but I know it's more related to some sort of line level issue and thought I might get better help in here.


I followed a tutorial to put a line out on a Google home mini which I am feeding into a class D amplifier board based off a TPA3116. This works brilliantly when there's audio coming from the Google home mini.


The "hack" is basically removing the speaker and putting a resistive divider on it's output to bring the speaker level output down to line level.



However, when the home mini shuts down the audio output as it's not doing anything (I'm assuming it turns off the amplifier to save power when not in use) I get a horrible ground noise hum.



I'm not sure how to tackle this. Someone in the other thread recommended putting a NE5532 preamp between the Google home mini output and the amplifier input. I tried this and it made no difference.



Has anyone any ideas? I'll try anything as I'm getting a bit desperate at this stage.

The amplifier is one of these if it matters:
Click the image to open in full size.




Thanks
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Old 10th October 2020, 08:29 PM   #2
cbdb is offline cbdb  Canada
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You know google is listening to you 24/7 thru that thing.

Google Home smart speakers let employees listen to your conversations

Last edited by cbdb; 10th October 2020 at 08:35 PM.
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Old 11th October 2020, 02:36 AM   #3
PRR is offline PRR  United States
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Hacked Google home mini to have a line out - weird ground noise issue when no sound.
> putting a resistive divider on it's output

Any values on that? Ohms etc?
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Old 11th October 2020, 03:48 AM   #4
leadbelly is offline leadbelly  Canada
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Well, I went and found the other thread, and it doesn't describe your hack. The devil is in the details: describe your hack in detail, preferably with a drawing.
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Old 11th October 2020, 03:55 AM   #5
DUG is offline DUG  Canada
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Some solid state sound sources open circuit their output connections when there is no output. ( like my phone ) This allows noise pickup by the amplifier due to its high impedance state.

Loading the signal line with a lower resistance ( 2K-5K ) has been known to help this issue.

You may have read that some class D amps come with a 50K pot on their front end and the recommendation is to change that to a 5K to reduce noise pickup at mid position.

Same idea.

If you are replacing the speaker with a resistor divider you should use low value resistors...in the order of 100 ohms.

Is the speaker in the Google a SE output or is it BTL class D to start with?
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Last edited by DUG; 11th October 2020 at 03:59 AM.
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Old 11th October 2020, 04:59 AM   #6
avtech23 is offline avtech23  Australia
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Hacked Google home mini to have a line out - weird ground noise issue when no sound.
Those Google minis use the Texas Instruments TAS5720 which are mono class-d BTL. They are all-in-one chips, so tapping in to an input isn't possible (Data in, sound out).

You might be able to isolate the output of the Mini to the Amp using a small audio transformer.

I recently used a Triad TY-144P https://au.element14.com/triad-magne...mer/dp/1824903 for a PAM8302 mini amp that would pick up horrible digital noise. All silent now.
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Old 11th October 2020, 02:15 PM   #7
bakeri is offline bakeri
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Leadbelly and PRR, I should have given more details. Apologies.

So I cut the wire going to the speaker, and then put a resistive divider across it which uses values of 3k and 33k. This reduces the max output of the Google Home mini to around line level. I got this information from this YouTube video: I DEFIED GOOGLE 😱 Hacked an Audio Port onto Google Home Mini (Mod Kit Available) - YouTube

The output cable which is going to the amplifier is across the 3k. Just rewatching his video, he uses a 300ohm and a 3K. I wonder is this why I have trouble? I wanted to use high value resistors to ensure they wheren't generating too muich heat...

Another difference between my version and what is done in the video is that I have not reconnected the speaker.

DUG I think you are on the right track with your 100ohm, but the issue is going to be heat generated...


avtech23: Audio transformers seem really interesting, but it's not something I would have used before.. Is t like a voltage transformer? could I get a 10:1 version and remove the need for my resistive divider altogether? Also thanks for the info on the google home mini amplifier. I had no idea what was in it.
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Old 11th October 2020, 04:21 PM   #8
leadbelly is offline leadbelly  Canada
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Yes, you did use too large in value resistors, especially since you are removing the speaker. Also, you never confirmed it, but you must use the exact same orientation as the video.
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Old 11th October 2020, 04:25 PM   #9
bakeri is offline bakeri
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OK, so do we think switching the resistor values to a 300 and a 3k will fix it?
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Old 11th October 2020, 04:32 PM   #10
leadbelly is offline leadbelly  Canada
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Personally, I would try 10 and 100 ohms, and use a larger wattage.
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