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:
Thanks
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:
Thanks
You know google is listening to you 24/7 thru that thing.
Google Home smart speakers let employees listen to your conversations
Google Home smart speakers let employees listen to your conversations
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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?
) 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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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-magnetics/ty-144p/audio-transformer/dp/1824903 for a PAM8302 mini amp that would pick up horrible digital noise. All silent now.
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-magnetics/ty-144p/audio-transformer/dp/1824903 for a PAM8302 mini amp that would pick up horrible digital noise. All silent now.
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.
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.
Thanks, I'll give it a shot!
On the power output. According to a source on reddit, the home mini has only around 5W output power.
If it was an 8 ohm speaker (worst case), then a 100 and 1000 ohm resistor pair, will put 1100 ohm across the output.
Am I correct in saying this would only put 138th of the output power across these, so even a quarter watt will be fine, or how have I completely misunderstood how this works.
On the power output. According to a source on reddit, the home mini has only around 5W output power.
If it was an 8 ohm speaker (worst case), then a 100 and 1000 ohm resistor pair, will put 1100 ohm across the output.
Am I correct in saying this would only put 138th of the output power across these, so even a quarter watt will be fine, or how have I completely misunderstood how this works.
Hi,
I want to give you all the information I can so we can try and find a solution, but I'm not really sure what you're looking for...
I just did a quick mspaint of the resistive divider. Can you tell me what else you need?
https://i.ibb.co/rmTdpt4/Untitled.png
(I had issues with the image upload here so used another site.)
I want to give you all the information I can so we can try and find a solution, but I'm not really sure what you're looking for...
I just did a quick mspaint of the resistive divider. Can you tell me what else you need?
https://i.ibb.co/rmTdpt4/Untitled.png
(I had issues with the image upload here so used another site.)
Does the speaker heat-up? Glow red in the dark??
Did you try sneaking it to a whisper and touching a finger to the resistor?
It's probably a 5V system? The lowest R value you mentioned is 100r. 5V steady in 100r is 0.25W. 5V peaks of speech/music in 100r is liable to be <<0.25W. And what is the worst can happen? A 12 cent resistor fire? Even if the whole HomeMini gets melted, Amazon would probably send you a new one. (I just saw on TV: Amazon can't possibly check all their returns, and most are bulk-auctioned to intermediaries and mostly put in landfill.)
@Leadbelly:
>Is it literally just the 2 unshielded wires to terminal blocks? No enclosure? No jacks and plugs? No other connections to other inputs? Power supply grounding?
Literally just the connections above with one terminal block. Nothing else connected.
I haven't detailed the power supply now that you mention it.
The home mini is on it's own 5V power supply which is powered from the mains and the amplifier is powered from a meanwell 24v PSU. I know the 0v rail between these two could differ and it would be probably better to derive a 5v DC supply from the MeanWell supply for the Google Home Mini, but it seems to work fine except for when the Mini goes to sleep.
@AVtech, Could you give me a link to something that explains what you're talking about?
@tomchr: A transformer to isolate the two seems like a great idea regardless. If it can do 10:1 ratio then it would be a great soloution. I've never looked at audio transformers before, what am I looking for?
>Is it literally just the 2 unshielded wires to terminal blocks? No enclosure? No jacks and plugs? No other connections to other inputs? Power supply grounding?
Literally just the connections above with one terminal block. Nothing else connected.
I haven't detailed the power supply now that you mention it.
The home mini is on it's own 5V power supply which is powered from the mains and the amplifier is powered from a meanwell 24v PSU. I know the 0v rail between these two could differ and it would be probably better to derive a 5v DC supply from the MeanWell supply for the Google Home Mini, but it seems to work fine except for when the Mini goes to sleep.
@AVtech, Could you give me a link to something that explains what you're talking about?
@tomchr: A transformer to isolate the two seems like a great idea regardless. If it can do 10:1 ratio then it would be a great soloution. I've never looked at audio transformers before, what am I looking for?
Just something like this:
It sometimes helps if there is a grounding issue, sometimes not. Either way, the diodes are very inexpensive so I usually give it a go.
The issue may just be that the leads you are using from the Mini to the amp are picking up all the radio garbage, which is then being amplified.
Shielded cables between devices are a good start.
It sometimes helps if there is a grounding issue, sometimes not. Either way, the diodes are very inexpensive so I usually give it a go.
The issue may just be that the leads you are using from the Mini to the amp are picking up all the radio garbage, which is then being amplified.
Shielded cables between devices are a good start.
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