Portable Audio Class-D Ground Buzz Problems

[qwaliti]

I have a Class-T amplifier, with a Bluetooth Module and a 12V battery. I get a loud deep Buzzing noise when I plug in the charger.
Can anyone offer any advice to get rid of this buzz.

I suspect it is a grounding issue.

 

[Speedskater]

That's why you dis-connect the charger when listening to music.

 

[qwaliti]

Yes thank you, but is there another way? i.e charging with no buzz?

 

[Speedskater]

Most people switch to battery power to eliminate the connection to the power company AC line.
However you could:
a] Get more batteries and swap them when they get low.
b] Replace the charger with a conventional amplifier power supply.

 

[nigelwright7557]

Chargers usually put out rectified AC.
This means there is 50Hz pulses on the power supply.

You could try a DC power supply of around 14 volts to charge your battery.
Not sure if it needs to be current limited or not.

 

[BassAwdyO]

I am having a similar issue myself using a XTPower powerpack(Amazon.com: XTPower 10000mAh External Battery Pack (Dual USB Output 5V plus DC Output 9V / 12V 2A) for Tablets, Netbook, Digital Cameras, DV Recorders, PSP, NDS, NDSL, GoPro, Smart Phones, Android Phones, iPhone 5, all iPhones, iPad, iPod, HTC Sensat)

to power a Lepai Class T amp (http://www.amazon.com/LP-2020A-Lepa...?ie=UTF8&qid=1397089827&sr=8-2&keywords=lepai)

and a bluetooth module(http://www.amazon.com/BestDealUSA-B...089932&sr=8-2&keywords=bluetooth+receiver+usb)


However, the issue I have is simply that the bluetooth is extremely noisy when powered by the XT power pack, charging or not.

Does anyone know if there is a way to clean up the 5v USB that is feeding the USB bluetooth dongle?

Even powered by the XTPower pack at 12v, the amplifier is essentially noise free at full gain without the module attached. Once the module is attached S/n is no greater than 30dB-40db which is extremely annoying.

I am considering trying this bluetooth module instead (Bluetooth Audio Receiver Board v2.1+EDR 12 VDC | 320-351) since it runs on 12volts, perhaps it will be cleaner...

Any thoughts? Opinions

Perhaps we can figure this out together...


Edit: I forgot to mention that the USB Bluetooth receiver has significantly less noise when powered via my computer's USB or via an apple USB charger. My theory is that the XT power pack has crappy converters from 12vDC to 5vDC which are inducing a lot of the noise....

Would an in line inductor in the 5v+ USB line be worth a try?? I'm kind of against buying the 12v powered bluetooth receiver from partsexpress just to try out and see what happens....

 

[marce]

Any chance of putting a scope on the output of the Xtpower pack. My bet its not that good on the output, also a photo of the insides would be interesting. and possibly revealing.
Seeing what the output looks like and seeing if there is any filtering, may just be possible to add some output filtering to the XT as a cheep mod.

 

[doctormord]

i'd try to add some 10nF from L+/R+ to GND on the line-connection between the BT-module and the amplifier input.

Additionally i'd try different values of ceramics on the power-input of the bluetooth module. (like 10/100/220nF to find a second pole to cancel noise somewhat) (From VDD to GND)

You may also add a chip-bead (inductor) inline the power-line.

PCB-pictures (and scope prints) would greatly help.

 

[BassAwdyO]

I can't really give you any pics of the XTpower's pcb as its somewhat of a sealed unit. In other words, no screws, nothing to take apart without breaking something.

I don't have a scope to look at the signal with myself. I've always been reluctant to buy one since I've never really got into circuitry that much, and it seems like good ones are expensive. Maybe I should check out the secondary market though. What kind of bandwidth would you suggest? 1Mhz, 1Ghz? Somewhere in between perhaps?

I'll get some caps and inductors and play around, Thank you for the suggestions!

 

[doctormord]

You may get an "OWON SDS7102E", or, the budged modell "OWON SDS5032E".

 

[BassAwdyO]

So, I have found a solution, if anyone is interested. By grounding the USB shield and neutral wire to the audio amplifier's ground the noise was greatly reduced.