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DIY bluetooth speaker

Batteries and bms are always connected, so i just say bms instead of batteries + bms. Connecting capacitors of different sizes and characteristics to bms, doesnt trigger the protection, so it cant purely be batteries fault. Connecting amplifier to bms triggers a connection. So maybe its some other element on amplifier that triggers a protection. Do you see anything from that picture ? The only difference i see is that i used different capacitors, at least they look different, but both are electrolitic ? I would really love it if i could trigger the protection using only capacitor :D
 

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audioguru

Well-Known Member
Most Helpful Member
The two 470uF capacitors in the amplifier are probably parallel with the power supply input making 940uF if they have typical capacitance but could be 1410uF if they have max capacitance. They are a dead short when the power switch is turned on until they become partially charged. Plus the max battery charging current might overload the BMS.

The amplifier circuit should not draw a huge current surge when it is turned on.
 
I thought the same thing about capacitors being parallel. So what i did was use 2 200V 680uF capacitors in parallel, making that a whooping 1360uF ! Couldn't trigger the protection. Then i went a step further and used a 40V+ 4800uF capacitor, a really big boy. Still couldn't trigger it. Maybe i could try like 4 or 8 parallel capacitors ? More caps in parallel, less resistance ... i would like to trigger the protection just to say oh, ok, this is what is happening. I really want to know.


Im not charging the batteries while doing tests. And i really think its the cell low voltage protection, not current overload. Because the bms shuts down until i connect the charger. Im gonna try with 4 or 8 caps in parallel. Im gonna trigger that protection or die trying :D
 
audioguru

I have a simple question. I changed a bluetooth amp in 1 of my speakers. Its basicaly the same brand, its similar only has added 2 more caps, it has different chip (TPA3116D2) and packs a bit more bass.

Yesterday i found a little problem with it. When you are connected to it and blasting at max volume, it will be usable, meaning there will not be much distortion, at least me and my 2 friends didnt hear it, it was usable music, we listened it for hours and enjoyed. But there was a problem with certain songs, if i had to guess it would be songs that are extremely loud as it is. When the really loud part started, the bluetooth would disconect, you could hear the beep, the music would stop, then it would connect again after a few seconds. To me this sounds like the amp used soo much power that somehow it didnt give enough juice to the receiver and the connection to mobile phone was reset.

First, am i making the right assumption ? And second, what would be the easiest way to solve this ? Would adding a big capacitor either on batteries or directly on DC input on amp solve this ? Having that big capacitor that could deliver enough juice to amp and prevent the bluetooth reset ? Again, this was only happening on maybe 100% volume and sometimes on 95%. 90% and under was ok. Some songs were ok even on 100%. But for when we are outside with lots of noises, we really like to use every single drop of loudness this speaker can offer.

Please dont tell me i have cheap amp, bad distortion that i cant hear and so on. I know i have all that, im working on extreme budget here. I am trying to find a cheap solution or at least try to find it. I already solved the problem with BMS protection kicking in simply by soldering a 50 cent capacitor to batterie pack output. I want to solve this cheaply and feel good about it. You know everything so i know you can help me :)
 

Diver300

Well-Known Member
Most Helpful Member
If you can separate out the power supply to the bluetooth part, you could try feeding that via a Schottky diode and adding a capacitor in parallel after the diode.

That way, if the amplifier causes the power supply to dip for a short time, the bluetooth part can run from the capacitor. As the bluetooth part of the circuit will take far less power than the amplifier, you can use a much smaller capacitor to achieve the effect you want.

If the voltage drop of 0.4 V from the Schottky diode is too much, there are active rectifier circuits using a MOSFET that would have a much smaller voltage drop.
 
I am not sure how i would do that, i would have to cut into the PCB board i think ? This is the amplifier that i am talking about. Right now my idea was to simply add resistor in parallel with DC input into the board. The problem is that i have no idea how to test if it works. I know at which song it disconected but i can crank up my speaker so loud at home. And that is a problem because the only time i can crank the speaker to maximum is when i take it out partying and if i find out that something isnt working, its already to late - we will have trouble listening to music all evening.
 

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Diver300

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I am not sure how i would do that, i would have to cut into the PCB board i think ? This is the amplifier that i am talking about. Right now my idea was to simply add resistor in parallel with DC input into the board. The problem is that i have no idea how to test if it works. I know at which song it disconected but i can crank up my speaker so loud at home. And that is a problem because the only time i can crank the speaker to maximum is when i take it out partying and if i find out that something isnt working, its already to late - we will have trouble listening to music all evening.
I hadn't read all of the thread and I didn't realise that the bluetooth device is part of the amplifier, so my suggestion isn't helpful.

Also, the input voltage range is quite wide (5 - 27 V) so it shouldn't matter if the input voltage fluctuates within that range.

I don't know what equipment you have available, but if I were having that problem, I would fit a resistor in place of the speaker for testing. That would allow me to put the volume up without anything being heard.

The resistor should be the same value as the impedance of the speaker, and have a larger power rating. The resistor will get hot if the testing goes on a long time.

If you want to hear what the amplifier is doing, put a higher value resistor, maybe 1 kOhms, in series with the speaker, and connect that as well as the high power 4 or 8 Ohm speaker to the amplifier. That way, the speaker will be quiet, but still audible, and the load on the amplifier will be close to what it would be if the speaker alone was there.

I would also monitor the battery voltage with an oscilloscope while the volume is up.
 
I will give it a test. Though i will try with more resistors too. Not sure if you read but i had a big problem with amplifier in that that when i turned it on, the BMS protection kicked in. The reason was that capacitors on amplifier when i turned the power on draw so much current, that either BMS thought it was a short, or it drew the batteries under 2V for a split milisecond and the BMS cut them off. I solved this by soldering a calacitor in parallel directly on battery pack. So when i turned the thing on, that capacitor helped charge the capacitors on amplifier and all was well. The problem came from a simple thing - this amplifier has a volume know that also turns the amplifier off when you turn it completely left. And when you use the knob to turn amp on, all is well. But i bypassed that know - i have it on max all times because i wanted to use separate button to turn the amp on (the reason being that if u only use knob, the amp will still use tiny amount of power - not a problem if u use AC power but a big problem if u use batteries, u let speaker sit for a couple of days and battery will be dead). And when knob is on max and u suddenly apply voltage to it, it will draw so much power that u actualy get a spark.
 
Ok audioguru, time for your expertise once again. Right now in my speakers i am using 2 "wuzhi" 2x50W amplifiers. First one costs about 5$ and has a no name chip, second one costs about 7$ and has TPA3116D2 on it. I am super super super happy with both amplifiers. I am using the later one right now as my main amp for my room stereo system. Before it, i had a pioneer amp, a furnace, that cost prolly around 150-200$ when it was new. And i swear to god i cannot hear the difference between the big pioneer amp and this tiny 7$ TPA3116D2. It was meant as a temporary solution until i buy a new amp but right now, i simply have no motivation.

Even though both "WUZHI" amps are rated at 2x50W, i feel that the 7$ one is a bit louder (at least my friends say so) and it packs more bass. At 100% volume the woofer membrane moves more and you can hear more bass. I also belive that there is less distortion at 100% volume than with 5$ amp, again, i am talking about what me and friends can hear, not about graphs. So in my opinion it is worth the extra 2$.


But now my question and i cant even belive i am asking you this, 2 years ago it was a fantasy. With this speaker i would gladly lose 3dB of bass and get 3dB more overall loudness. Meaning it will have a tiny bit less bass and tiny bit more loudness. Barely noticable but still, it would be a good tradeoff for me. Now an easy solution would be just to change the length of bass port to go less low but give it a slight boost at around 80-120Hz. But that will again increase the bass effect (boomy thingy u called it) and whats worse, it will completely mess up with my schematics. I made excel sheets where i have all the data and it calculates the exact dimensions of wooden parts and port. And as it is, the stupid port is taking a huge chunk of my speaker. So i am wondering is there any other simple solution to do this ? Without changing the amp and investing huge amounts of money since im on a budget. Looking for a new woofer also isnt a solution. This dayton is the only thing in its price range to be useful, i mean if i am to belive the data, its far ahead of everything else u get for 14$. And if i cant belive the data its all for nothing anyway since i dont have a studio equipment.


And a sub question. Right now i use 3L wooden box for the speaker. But it would be nice to make 1 for me thats like 4 or 5L, a special speaker just for me. How the hell am i going to find a speaker for that ? The one i am using kinda peaks out at 2L meaning when u go over 2L, you barely see a change in the graph. But when i went through all possible bigger speakers (dayton is 4", i went checking 4.5" and 5"), they all needed a LOADs bigger box than 3L. So i am either stuck with this one at 3L or i need a 8L box for an 4.5" or 5". And 8L is like my backpack.
 

audioguru

Well-Known Member
Most Helpful Member
An amplifier has a maximum continuous output power with low distortion. If you try to get more power by turning up the volume control then the amplifier output will produce clipping distortion. Acid Rock "music" is already distorted then you will not notice amplifier clipping.

An amplifier is designed to have extra gain so that low level input signals can be made loud enough. Then the volume control is turned down with normal input levels to avoid clipping distortion and the volume control is never turned up to maximum with normal input levels like you are doing.

Most audio amplifiers are designed to produce frequencies from 20Hz to 20kHz all at the same level. Some cheap amplifiers reduce their cost a little by using smaller coupling capacitors that do not pass low frequency levels enough.

Most speakers have a recommended sealed box size and ported (vented) box size. If you reduce the box size then the bass might sound boomy and there will be a cut of lower frequencies.
 
The boxes and everything else is identical, except 2 different amps but they look very similar, both 2x50W. First one will never disconect when on max volume. Second one will on certain songs reset the bluetooth, or maybe the whole amp will disconect. So lets just speculate here:


Could it be that it simply draws to much power and all that power goes to the amps so it runs out of juice to run receiver (bluetooth) and that is why it disconects ?


And if that is indeed the posibility
... even a 0.00001% posibility, would 1 way to test it be that i solved some additional capacitors to terminals both of batteries and of the amp itself ? The theory being, that this capacitors will quickly deliver some extra juice to the amp and prevent the disconect ?
 

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