Bluetooth diy speakers, hiss :O

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tigox

Member
2012-07-10 7:24 pm
Hello, first of all let me just apologize if this thread is in the wrong section, i didn't know where to put it because of it's nature...

So, i have a problem with the speakers that i'm building, if anyone could help me i would appreciated so much because i really don't know what to do know....

the problem is: i custom made portable speakers, these consist of an sta540 2.1 amplifier from ebay (all links in end of post), a sure electronics bluetooth module, 2 winmax 11.1v 5200mah batteries and respective pcm boards, and some speakers i had laying around..
these speakers had never had any Hiss or noise in the music, they had a surprising and superior sound quality but that was before i installed the bluetooth module last night, i made the board just like the schematics in the bt module's pdf, i tested it outside the speakers using an ATX power supply and it was just awesome quality and volume (without any external amplifier, just the module), then when i put it inside the speakers connected to the same power source as the amplifier, and connected the audio to the same input on the amplifier's board as the rca's it started making a horrible VERY LOUD hiss, so by then i didn't know what to do.. and later besides the hiss, the sound from the bt's module just turned awful, very distorted even at very low volume, sorry for the long explanation, has anybody have any idea ? :S

ps: i tried a 10uF cap. in parallel with the tweeter's output, and also tried decoupling the power source (the output of pcm board, for protection against battery over-discharge) with a 10nF capacitor.



Bluetooth module: http://www.sure-electronics.net/mcu,display/MB-CM15113/MB-CM15113%20Manual.pdf


STA540 2.1 Amplifier:sta540 2.1 | eBay


My pcb layout of the bluetooth module:


NOTE: the three pins on the farthest left are the lm317 regulated to 3.42V






2z6i7f8.png


Thank you in advance for your help :DDD
 

aditya

Member
2010-03-06 3:09 am
Bombay
i dont know if you fixed it but the thing is that it needs alot of ground and if you can manage that then the issues go away, and keep a copper clearance of atleast 20mm ( normally they say 15mm but i would say 20mm. secondly use 2200uf at input and output of 7805 ( get better variant ). thirdly keep a single common ground to avoid ground loop.
the thing with bluetooth is we need a lot of ground to absorb the noise...

currently facing it.

my issue was i was using a shielded bluetooth module by Microchip - BM20, i had used less groundpour and i was also getting the clicks and hiss and modem like noise on audio.

so i put thick wire from bluetooth ground to preamp ground and the hiss and click and modem noise on audio line was reduced to like 90%

hope this help.. else ping me :D
 
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