Problem with my music player

[RichardW]

Hi, I recently built myself a music player, by combining the following:
- a little clip-on mp3 player (not sure i should post a link here, but it's the cheapest you can find on ebay.)
- a PAM8403 amplifier board. (2.5 - 5.5v)
- a 5 volt ac-dc power supply.
- 2x 8ohm speakers.

The 5v supply is suitable for both the amplifier and mp3 player, as they are both designed for usb connection. The psu does measure 5 volts.

However, when I connect these together, something is wrong. On connecting power, the speakers produce loud clicks at a rate of about 4Hz. Sometimes this clicking dies away after about 10 seconds and the music plays normally. But sometimes it persists, and I will unplug it out of fear that something is going to break.

Each device on it's own (mp3 player / amplifier) works great. Wondering if is a power issue, I have tested both devices powered simultaneously with the mp3 player driving headphones, and the amplifier driven by another audio source, and this seems to work ok. It's only when they are connected together (mp3 audio output->amplifier input) that this clicking happens.

I have tried adding capacitors to the power lines in case that was the issue, but it has had no effect.

I'm really not sure where the problem lies, whether it's a power issue forcing one of the devices into an on-off-on-off cycle, or a coupling issue, or some weird feedback issue from sharing the same psu.

Please help!

 

[Harald Kapp]

Welcome to EP, Richard.

Show us a schematic of your setup including the power wiring as it is in reality (from where to where do the wires go?). You might have an issue with a ground loop or similar.

 

[RichardW]

 

[Harald Kapp]

Try connecting the power supply to the amplifier directly to the power input of the MP3 player to minimize the loop which can pick up stray electromagnetic fields.
There's no guarantee this will improve the performance as stray Em fields typically produce hum, not a click noise.

Are you sure the dc-dc adapter is designed to deliver the amperage required by the amplifier? "Clicking" sounds (pun intended) like the power supply is periodically interrupted which may be an indication of overload.

 

[cjdelphi]

I'm suspecting there's not enough current available, lowering the volume help?, (on low)

 

[RichardW]

I'm suspecting there's not enough current available, lowering the volume help?, (on low)

Are you sure the dc-dc adapter is designed to deliver the amperage required by the amplifier? "Clicking" sounds (pun intended) like the power supply is periodically interrupted which may be an indication of overload.

I feel I have already tested for this. As I said in my first post, I tried powering both devices simultaneously, but without the audio connection between them: The mp3 player driving headphones, and the amplifer driven by a seperate audio souce, and that combination seems to work ok. It should be the same power draw.

Furthermore, if/when the clicking stops after 10 seconds, the music plays normally, and I can turn the volume as loud as I like, and the sound is not interrupted. The problem only occurs during power-on.

Try connecting the power supply to the amplifier directly to the power input of the MP3 player to minimize the loop which can pick up stray electromagnetic fields.
There's no guarantee this will improve the performance as stray Em fields typically produce hum, not a click noise.

I had not heard of ground loops before you mentioned them yesterday. I read that it happens when two devices sharing the same power supply have another connection between them, which I might have here, because of the audio cable.

I did a resistance test on the amplifier, and the audio ground to power ground is 0 Ohms, so it could indeed be a loop.

But you are right that there is no mains hum, so I doubt this loop is picking up stray fields. But it could still be causing current to flow the wrong way to ground. eg, if the amplifier is grounding power through the audio cable, through the mp3 player -OR- (and this seems more likely to me) the logic circuits of the mp3 player are grounding via the audio cable, through the amplifier. Either way, it's not the proper path.

So... I decided to try using non-direct coupling between these two devices. Experimenting with capacitors, resistors, etc. And it turns out that I don't actually need the ground wire in the audio cable connected to anything. Disconnecting this wire completely seems to have solved the issue. I am a little in awe to be honest that the audio signal can get through without the ground wire there!

However, I would like further guidance, as to whether it's okay to run it in this state. Is there a more professional solution? "Cutting the black wire" just seems too much like a duct tape solution.

 

[KJ6EAD]

I'm guessing that one or both devices has a signal ground that's above the level of the power ground. Assuming no change in the power connections, you can use audio transformers to couple each of the audio signals (left and right channels) from the player to the amplifier. This will isolate the player signal ground from the amplifier signal ground.

 

[cjdelphi]

A ground loop is 1:1 ratio transformer to stop hum and other things

If that is the problem placing a larger capacitor across the voltage rails will reduce the clicks and hum (i've never had this issue with the pam amplifier)

 

[RichardW]

A ground loop is 1:1 ratio transformer to stop hum and other things

If that is the problem placing a larger capacitor across the voltage rails will reduce the clicks and hum (i've never had this issue with the pam amplifier)

I tried upto 4700uF, and it had no effect. At this stage, I'm believing the power supplied to the devices is adequate.

Over the past week I have tried power supplies of three different designs (regulated transformer, switchmode, battery pack) and the behaviour is the same in all cases.

I'm guessing that one or both devices has a signal ground that's above the level of the power ground. Assuming no change in the power connections, you can use audio transformers to couple each of the audio signals (left and right channels) from the player to the amplifier. This will isolate the player signal ground from the amplifier signal ground.

The amplifier's signal ground measures 0 ohms with the power ground, so I expect the voltage level there to be equal (ie, 0v). I've no idea about the mp3 player however.

But proceeding on the assumption that you are right, that the mp3 player has a different signal ground than power ground, then imagine if the mp3 player is getting into an on-off cycle, then the mp3 player's signal ground will repeatedly be brought up and dropped down. The amplifier would boost this sudden voltage change into loud clicks. That could be one possible explanation.

Your suggestion sounds promising too: Using transformers to couple the player and amplifier will certainly separate their grounds, and remove loops. If I can find any suitable audio transformers in my electronics bitbox, I will try this out, and get back to you! Thanks.

 

[RachelGomez161999]

Potential solutions:

Unfortunately, the Play Music app doesn’t have a way to identify and delete duplicate tracks, so the only workaround is to delete the entire collection and re-upload it. Make sure that doubles aren’t already present in the library, and then re-upload it.
There is a workaround available that was created by a Reddit user, and you can find the step-by-step guide here. Keep in mind that technical know-how is definitely recommended if you are planing to follow this route.

Regards,
Rachel Gomez

 

[Harald Kapp]

@RachelGomez161999
#1: this thread is from 2016 without any further replies since.
#2: your post completely misses the problem which is based in hardware.

I'll close this thread.