Noise from bluetooth receiver module.

Lately i was building my 5.1 channel amp based on 2050 for my yamaha NS-P40 speakers. And i borrowed contol boards from an old 5.1 china home theatre speaker system. So that i have inputs from aux, 5.1 channel dvd, fm, sd, usb, and bluetooth.

And everything works perfectly.and 2050 seems perfect ic for the speakers. Gives rich tones.. and i love the way they sound. Though i never impliment sub woofer amp, just because my sub which came with NS-P40 is a powered one. And i just looped an audio out from my control board and its all ok.

And to avoid pop noise while i power off speakers, i used a relay to control power to amp chips ( the relay cuts of the positive and negative rails instantly when i turn off the amp, so no more pop noise , but i dont know if its a safe setup, and for now the relay dont have delay circuit, so lil bit pop noise is there when i power on, as the relay acts instantly, before the capacitor charges ; later i will fix that too with a delay circuit).

My problem is now with bluetooth audio . There is a pop noise when i turn on bluetooth section, or when i press buttons on remote contol ( then amp picks up 455 khz tones/ the operating frequency of ir section), and also there is single pop when ever the song changes ( ie the audio stream goes from mute to active). This is so much annoying.

But there is no such problem with any other sections like fm/usb/sd etc ( where the fm receiver ic / usb dac/ is built into the same contol board with bluetooth module) . Nor with aux or dvd inputs ( i use a 7.1 dac to get analoge outs from my laptop's usb , where dac is using cmedia dac ic). Everything else seems silent and not even a slight hum or noise is present even when i listen with ears on speakers ( as i added heavy capacitor filters and polyster disc capacitors to filter ac noise. And also use elna capacitors for construction of amp.) .

I did some modification on 5v supply for bluetooth. Insted of default 100mf filter capacitors which was present alredy along with 7805 ic, i replaced those 100mf with 470mf ones. Also add .1uf discs to get clean outputs. The weired thing is i only did that modification for the control board section. And before that there was no noise or nothing.. after trying to get more cleaner dc, now there is this pop when ever i use bluetooth section.

Though i didnt get time to revert back the capacitors and check, i belive its that increased capacitor values that cause the problem.


Does any one have any explantion on this strange thing??? How can adding more farads to filter the dc affect the bluetooth ( or contol board) secton??

I hope some one have experinced similar thing.. btw.. i use two transformers for amp an contol board ( torroid for powering amp and normal 9v 500 ma transformer for powering control board.).

Can anyone give an explantion for what might be the problem.
 

tomchr

Member
Paid Member
2009-02-11 12:58 am
Calgary
www.neurochrome.com
The pop you're experiencing when you turn your amp on/off is caused by the output stage of the op-amps biasing and de-biasing. The only way to fix this is by a mute relay on the output.

If your amp is picking up 455 kHz, you need to add an RF filter on the input of it.

The pops between songs on the Bluetooth module is probably a flaw of the module itself. Maybe it mutes/un-mutes when the song changes somehow creates a discontinuity. I think the correlation with the supply capacitance, and by the way I assume you mean uF and not mF, is probably coincidental. Unless you're browning out the regulator. Measure the voltage from input to output on the 7805 IC and compare with the drop-out voltage specified in the data sheet.

Tom
 
Any update on this issue?
I also encountered this issue on my previous project here:
Bluetooth Speaker Project – tataylino.com
Solved it by connecting the OUTN of the bluetooth module to the INN of the amplifier instead of connecting them both to ground. Now I got a new project which the amplifier INN is permanently connected to ground so that fix wont be applicable. I am looking for another fix. Perhaps I need first to understand how the popping sound is produced. I just have no time to investigate for now.