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MP3 player hum

Audioguru

Sep 24, 2016
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Hum is simply filtered away by cutting all the bass sounds.
 

BlueObsecurit

Mar 24, 2021
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could it be the "seeduinio"?
No, noise is still present without the microcontroller.

Probably follow Harald's advice.
I've already checked if the power supply is responsible, so I guess you mean the bit about short connections and ground.
I've rewired everything, kept it short, had a minimal version, avoid using daisy chaining etc, etc. It does not at all affect the noise, it is constant. If I play at max volume the noise goes away.

I think what I need is a filter on the audio output. In any case, that's what I'd like to try. But I have no idea how to design that, or what values should be used, etc. Are anyone able to help with that, or will that not work for some reason?

The other alternative is to get a stereo pot. What value would be good to choose?
 

Audioguru

Sep 24, 2016
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If the hum is a pure sinewave with no harmonics (but it probably has harmonics) then a filter for that frequency will cut some parts in music and in speech. But with harmonics then you must cut all bass frequencies which is bad for music and makes male adult voices sound like chipmunks.

My sound systems and many I made over the years produced no hum.
 

BlueObsecurit

Mar 24, 2021
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If the hum is a pure sinewave with no harmonics (but it probably has harmonics) then a filter for that frequency will cut some parts in music and in speech. But with harmonics then you must cut all bass frequencies which is bad for music and makes male adult voices sound like chipmunks.

My sound systems and many I made over the years produced no hum.
Right, this is what I feared. Oh well, suppose step free volume control isn't so bad...
We're dealing with a sub-par tiny module with a ton of idiosyncrasies, I suspect that is why and short of redesigning the module, I won't have much luck finding the actual source of the noise.

10K logaritmic pot be alright for this?
 

VenomBallistics

Aug 30, 2018
285
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one last thing to try ..... chokes in the outputs like they do for class D amps something in the range of 7uH to 33uH is what I get from a random scan of datasheets.
Option B
10K should be sufficient, assuming you're going into some kind of amp.
And yeah ... I looked at the application list for that module ... Strange that is has removable storage, yet they recommend it for applications similar to a talking greeting card.
 

BlueObsecurit

Mar 24, 2021
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something in the range of 7uH to 33uH
I'll try this when I get somewhere it's possible to buy components...

10K should be sufficient, assuming you're going into some kind of amp
That's just the thing, it will be doing both. Headphones and amp -> larger speakers. I tried reading up on this, but didn't get too far, should I get less, such as 1K?

And yeah ... I looked at the application list for that module ... Strange that is has removable storage, yet they recommend it for applications similar to a talking greeting card.
Oh yeah, there is provision for flash memory playback, and the ""pro"" version has like 128mb of it. Not sure if that means the one I have doesn't have flash, or if it does because neither of the other playback sources - some of which I have - are documented. You have SD, USB (referenced as "u-disk"...), aux (?), sleep (??) playback too. How do you access

While we're on the topic, volume function has to be called twice (Guess how long that took to figure out), if you place files in the root of the SD card it has to be 000x.mp3, but if you place it in a folder it has to be 00x.mp3. despite all of these functions and redundancies, I've had to make my own shuffle function, because it only has "random" which doesn't care how many times it repeats one song in a row... It has "IO" input for next/prev and vol+/- and also you can hook up an array of 20 buttons to handle those functions, where 14 of those buttons just do "segment XX" (???)

Point being, I really think something with the module that I can't do anything about is causing this sound. I also checked another module, same exact noise. I've learnt a lot and been frustrated a lot too, but reading over this does make me laugh at all the weirdness.
 

VenomBallistics

Aug 30, 2018
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I'll try this when I get somewhere it's possible to buy components...


That's just the thing, it will be doing both. Headphones and amp -> larger speakers. I tried reading up on this, but didn't get too far, should I get less, such as 1K?


Oh yeah, there is provision for flash memory playback, and the ""pro"" version has like 128mb of it. Not sure if that means the one I have doesn't have flash, or if it does because neither of the other playback sources - some of which I have - are documented. You have SD, USB (referenced as "u-disk"...), aux (?), sleep (??) playback too. How do you access

While we're on the topic, volume function has to be called twice (Guess how long that took to figure out), if you place files in the root of the SD card it has to be 000x.mp3, but if you place it in a folder it has to be 00x.mp3. despite all of these functions and redundancies, I've had to make my own shuffle function, because it only has "random" which doesn't care how many times it repeats one song in a row... It has "IO" input for next/prev and vol+/- and also you can hook up an array of 20 buttons to handle those functions, where 14 of those buttons just do "segment XX" (???)

Point being, I really think something with the module that I can't do anything about is causing this sound. I also checked another module, same exact noise. I've learnt a lot and been frustrated a lot too, but reading over this does make me laugh at all the weirdness.
That's about where I would be parked on the issue too.
Also, I'm left with the question of what this module is really for. You don't really need a removable card for what it seems intended for. You could just load audio via USB to permanent flash memory.
I guess it's smaller than an old condemned smartphone and a bit easier than a raspbery pi zero
 

BlueObsecurit

Mar 24, 2021
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Thought I'd give a small update on this.
The stripboard did not help. My idea was then to simply add a potentiometer when I could get one, however I have headphones with one included and I noticed that the noise always goes away at a certain setting. So I measured it, found out it is about 100Ω, put in two 220Ω in the audio lines, and it now works perfectly.

I think it must be a particular issue with headphones because they are very close to the ears. There is still some noise if you put your ear very close to something else, like a speaker, but this is comparable to if the speaker plays audio from my phone.

Also, I'm left with the question of what this module is really for.
Everything. Which is a blessing and a curse in this respect. My motivation for this project is to seperate music playing from my phone, as it is a lot heavier and cumbersome to operate, if your phone in your pocket and get a text you gotta fish it out, unwrap the cord send a text and try to stuff it back in. (among other reasons why) This project has tactile buttons for everything and can be operated from memory. I'm happy to report that I'm getting there!

Thanks everyone who helped.
 

VenomBallistics

Aug 30, 2018
285
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Don't know about you, but the strict numeric file naming conventions would drive me nuts.
I've pondered a similar project for automotive environments. Music and travel appropriate functions, tactile interface, and minimalist visual feedback. The whole idea revolved around the principal of your eyes belonging on the road and your hands on the wheel.
But the target vehicle didn't make it much past it's 30th birthday
 
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