So I have here sub woofer Simbadda CST 5100N and I want to convert it to bluetooth, so bought an MP3 bluetooth module to convert it. The module needed 5 to 12 volt DC to operate. Inside the speaker, there is step down transformer 220 to 9 volt (that is what is written on the transformer), but I connected the power supply for MP3 module from a capacitor after full bridge rectifier. Before I connected it though, I measured the voltage running through the capacitor (2200 uf), and it says 12 volt. So I can directly connect the module and it would operate. On the module though, there is LM 7805, so I know it runs with 5 volts. The problem is the humming sound is louder. Is there anyway I can reduce the humming sound ? Or it would be best to eliminate it.?
Electrical – Any solution to avoid humming sound / speaker noise for MP3 bluetooth module
modulemp3speakers
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Your limiting factor is probably voltage swing.
If your driving higher end headphones your probably looking at a 250->300 ohm load, 300ohm for higher end sennheiser cans for instance. But some phones (mostly professional models) can go as high as 600 ohms.
At 300ohms:
For 100mW you need 5.47 Vrms = 15.48 V peak-to-peak ( 18mA RMS)
For 200mW you need 7.75 Vrms = 22 V peak-to-peak ( 25mA RMS )
You probably won't find an integrated part that is specifically designed for portable devices that can achieve those levels of voltage swing. Your best bet is probably an audio op-amp with a high drive current (TI makes several, as does analog devices) or a purpose built headphone driver, for instance the TPA6120A2 would fit your needs.
Your challenge is then to build an efficient power supply to generate the +-12-15V rails needed.
Not sure what your plan it for batteries but one way to make it easier and more efficient is to use two batteries, maybe two 9V batteries, center tap for ground giving you +-9V rails to start with. You end up with bigger/more batteries but you don't lose any power boost converting up to your + rail and then using a charge pump or similar to get your negative rail.
EDIT: I'd target 100mW MAX...200mW would explode your head with most phones. expect 97-102db sensitivity at 1mW for most higher end cans (could be lower for pro models). meaning at 127mW you'd be looking at SPL in roughly the 115dB to 120db range which is more than enough to cause hearing loss if listening for extended periods. Targeting ~63mW would put you at 112db -> 117dB which eases your voltage swing constraints and can still cause plenty of ear damage.
I just noticed: In your video, the power supply is set to 7.8V.
The chip needs something between 8 and 28 V to work properly.
So you're simply operating out of the specifications of that IC.
Increase the voltage to at least 10V. Use proper (read: much thicker than what you're currently using) wires for power supply.
Again, the IC is positively ancient. It doesn't have any undervoltage detection, so it's no surprise that
When I start about @ 2.3V, the sound is somewhat good, but very quiet. When I bump it up to about 4V, the sound it totally distorted.
since you're practically pushing the sound input through insufficiently biased transistors.
When I rise it again to about 7V, the sound is really good, but one of the speakers starts to do that tick tick tick...
aligns very nicely with that.
When I connect both speakers to one channel, even at bigger volumes, it goes just fine.
Yeah, then you reduce the load impedance, and thus, the voltages that the transistors can supply get lower, and your sound gets compressed to a smaller voltage range. I'd claim "it goes just fine" is not really true. It might sound like you hit the "loudness" button on an 70's stereo.
I'm still recommending a not-as-obsolete amplifier ICs. There's literally thousands out there which aren't as terrible.
I do personnally know the seller and he sells a lot of these every day, so he has to buy new one like every week or so.
It's nice that you know your seller personally, but he's selling you ICs that are marked as "obsolete" at digikey, mouser and other larger retailers, and that the original manufacturer (ST) doesn't even list anymore. In other words: he's selling you the crap that no-one but beginners, who don't know better, buy, or people that have to repair ancient amplifiers. Even if DIY audio enthusiast often swear by some older amplifier designs, this IC is simply not worth using in the year 2017. There's nothing comparably good about it.
Go to the website of the former manufacturer of the TDA2009A (it's http://ST.com), click through the audio amplifier ICs and select a Class AB amplifier (modern class AB will sound a lot better than class B, and be much more efficient than class A, I actually don't find class B in the wild very often anymore; they're basically bad amplifiers, to be honest) and build the schematic from the datasheet. You can often get them for free as samples, or for little money at online retailers.
Don't just buy anything your local seller recommends. He probably has a stock or an extremely cheap source of obsolete parts and is trying to make money with inferior products. That is bad style.
Best Answer
The problem is a ground loop, or possibvly a short-circuit caused by the common connection of the audio signal
To fix it use an audio isolating transformer to carry the music signal between the MP3 player and the amplifier board