Hello
I have made a streaming music player to equal or better my Panasonic transistor radio, so not A1 quality.
I have a Pi 3 b+ running pCP, feeding a PCM2704 Dac, feeding into a TPA3116D2 Digital Audio Amplifier Board Module DC 5-28V VBU. Its all in a box with a 7"Hdmi screen. Power supply is 12v from any number of psu's, and 12v is dropped to 5v for the Pi by a 12-5v convertor.
Its noisey. What can I do, any way to decouple anything.
If I run the Pi from a separate stabilised 5v supply, its quiet, almost, or good enough.
Any ideas to keep only 12v input.
Thanks
thyristor44
I have made a streaming music player to equal or better my Panasonic transistor radio, so not A1 quality.
I have a Pi 3 b+ running pCP, feeding a PCM2704 Dac, feeding into a TPA3116D2 Digital Audio Amplifier Board Module DC 5-28V VBU. Its all in a box with a 7"Hdmi screen. Power supply is 12v from any number of psu's, and 12v is dropped to 5v for the Pi by a 12-5v convertor.
Its noisey. What can I do, any way to decouple anything.
If I run the Pi from a separate stabilised 5v supply, its quiet, almost, or good enough.
Any ideas to keep only 12v input.
Thanks
thyristor44
There is a ground loop in your system, the current draw by both the raspberry pi and the amplifier are being converted to voltages by the power supply wires, and because they share the same power supply, those voltages are being fed into the amplifier's audio input.
You need to break the loop somehow, you can use an isolated DC-DC converter to feed the raspberry pi, you could use a usb isolator, or you could use a line level audio isolator.
When using an isolated DC-DC converter, or a usb isolator, there might be a capacitor connected between the input and the output, which might still cause a ground loop at high frequencies, so that might not fix your problem.
A line level audio isolator does not have such a capacitor, but the transformers in them will add a bit of distortion.
Another option is to use an amplifier that has a differential input, which will filter out the voltages generated by the current draw from the power supply.
You need to break the loop somehow, you can use an isolated DC-DC converter to feed the raspberry pi, you could use a usb isolator, or you could use a line level audio isolator.
When using an isolated DC-DC converter, or a usb isolator, there might be a capacitor connected between the input and the output, which might still cause a ground loop at high frequencies, so that might not fix your problem.
A line level audio isolator does not have such a capacitor, but the transformers in them will add a bit of distortion.
Another option is to use an amplifier that has a differential input, which will filter out the voltages generated by the current draw from the power supply.
Exactly, the culprit is the ground loop. Fortunately your TPA3116 amp has balanced inputs, on some boards quite easily usable. It worked in my case very well Adding an Amp into Thin-Client PC
Thats interesting, the ground loop theory. I have found if I power the player with separate supplies, 5v and 12v there is virtually no noise.
I will check if my amp has balanced inputs but I don't think the PCM2704 dac has balanced outputs.
If I disconnect the input to the amp and connect the ground output from the dac to ground input to the amp there is no noise.
I will check if my amp has balanced inputs but I don't think the PCM2704 dac has balanced outputs.
If I disconnect the input to the amp and connect the ground output from the dac to ground input to the amp there is no noise.
Look at the link I posted, the soundcard has no balanced output either. Use a standard single-ended to balanced connection. All you need is disconnect the cold-input capacitors from ground and feed them with ground at the DAC output, using proper balanced cable at best (shielded microphone cable, shield connected at the DAC side only). The common-mode ground noise at the DAC output against the PSU ground will be subtracted by the balanced inputs.
phofman I wish I had seen your articles on your player before I started, they are very helpful, thanks.
I had a look at my TPA3116 board its too small for me, never worked on surface mount at all. I see exactly what you mean though.
Any ideas for cheap differential input amps that are cheap.
I had a look at my TPA3116 board its too small for me, never worked on surface mount at all. I see exactly what you mean though.
Any ideas for cheap differential input amps that are cheap.
The cheapest differential input amp is a TPA3116 amp with available differential inputs, such as the one I use DC 12V 24V TPA3116 Dual Channel Stereo 50W*2 BTL Mono 100W Audio Amplifier Board 9934840364132 | eBay
As I wrote some time ago in another forum ("Class D"):
"You should connect all ground lines together ("star grounding").
I had the same issues initially when I set up my (similar) project (all three components - RasPi, DAC and amplifier - powered by the same power source).
Once I joined all ground lines to one central point, the noise disappeared.
BTW, my line out from DAC to amp has ground disconnected - I only have left and right channel signals from DAC to amp (i.e. two wires instead of three - ground is NOT connected).
Try that, and I think your noise problems will be solved. "
I addition to what I wrote above, I might add that in the end I *did* connect the amp signal ground: but again - not to the incoming signal ground from the DAC, but to the main "star ground". Without that last step, I still heard noise coming from wifi activity on the RasPi
This is the main and most common issue when powering both the RasPi (and DAC) and the amp from the same PSU (regardless of any step-down modules you might use).
Some "ground isolators" might help (a bit), but you won't solve the problem until you ground everything as described above.
No use in buying extra components (I also tried isolation transformers, and many other gadgets.... no use, nothing solved the issue completely): just gound everything into a central ground point, and your noise will be gone
"You should connect all ground lines together ("star grounding").
I had the same issues initially when I set up my (similar) project (all three components - RasPi, DAC and amplifier - powered by the same power source).
Once I joined all ground lines to one central point, the noise disappeared.
BTW, my line out from DAC to amp has ground disconnected - I only have left and right channel signals from DAC to amp (i.e. two wires instead of three - ground is NOT connected).
Try that, and I think your noise problems will be solved. "
I addition to what I wrote above, I might add that in the end I *did* connect the amp signal ground: but again - not to the incoming signal ground from the DAC, but to the main "star ground". Without that last step, I still heard noise coming from wifi activity on the RasPi
This is the main and most common issue when powering both the RasPi (and DAC) and the amp from the same PSU (regardless of any step-down modules you might use).
Some "ground isolators" might help (a bit), but you won't solve the problem until you ground everything as described above.
No use in buying extra components (I also tried isolation transformers, and many other gadgets.... no use, nothing solved the issue completely): just gound everything into a central ground point, and your noise will be gone
Add PSU output EMI filters
Add PSU output EMI filters, and All output add a short ground wire to the motherboard metal base.
Add PSU output EMI filters, and All output add a short ground wire to the motherboard metal base.
An externally hosted image should be here but it was not working when we last tested it.
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