DIY bluetooth speaker

[SentinelAeon]

Like i said, on/off switch doesnt affect amplifier, only when power is coming off affects it. If it is OFF and microusb is plugged in (and battery is not), it will run the amplifier through microusb power. If its ON and battery is inserted, it will use battery power. I saw online tutorials where they just connected 5V directly to microusb.

Anyway i will unsolder the switch. That i hope means that it will be completely off no matter where the power is coming from. Then i just have to figure out which pins to connect to make it work through microusb. I have some simple switches from old power suplies, they should do the work.

 

[SentinelAeon]

I saw some guides online to use this bluetooth amps. And i saw them putting a capacitor between amp and batteries. Is that worth doing since i have plenty of capacitors left ? What good will that do ? Smooth out the voltage ? Will it also help when amp needs more power for a split second ? For instance when there is a part of song with extremely high frequencies ?

 

[audioguru]

A capacitor stores a charge that can be used to supply a high current for a moment.
You never connect a capacitor "between" the amplifier and its batteries, instead you connect them in parallel so the capacitor can supply power for a moment when the battery craps out. Your amplifier circuit probably already has a capacitor or two on it parallel with the battery. If the battery is discharged, weak or old then a few thousand microfarads capacitor parallel with it will make loud music sound better.

High audio frequencies are usually at low power. Deep bass and drum beats use a lot of power.

 

[SentinelAeon]

Ok i uploaded a new picture with the capacitor, does this look ok ? I have plenty of capacitors so it cant hurt to add them. What voltage and capacitance do you recomend?

Btw looking at this amp, it already has a couple of capacitors. So if i add more, in theory, will loud music and maybe bass sound better with added capacitors ?

 

[audioguru]

All capacitors have the capacitance in microfarads printed on them, but yours doesn't so its capacitance might be too small to do anything.
It must be at least 1000uF if the battery has discharged, is weak or is old to improve the sounds of deep bass beats or drum beats but it will not make all the music sound better.

The Chinese boards have no details about them so I do not know if the battery voltage stepup circuit prevents the battery from being destroyed if the battery voltage drops below about 3V by sensing the low voltage then turning off the battery.

The amplifier is designed to be powered by one 18650 cell and has a battery charger circuit on it so why are you fiddling with a voltage booster and a switch? The difference in loudness between using the fully charged 4.2V battery and 5.1V will be small. I doubt that the voltage booster has voltage regulation to keep its output at 5.1V when the battery voltage has run down. The boosting will cause the battery to run down quicker.

 

[SentinelAeon]

I am doing the thing with the stepup because i dont trust the amp enough That stepup of mine will also be a charger, with 2.8V - 4.2V protection.
As for capacitor, i will make sure it si at least 1000uF. What about voltage, since i am working with 4.2V voltage, will 10V be ok ? or maybe between 10V and 30V, have to check which one i have.

 

[audioguru]

I also do not trust the amp:
1) It is Chinese with no-name-brand and unknown ICs.
2) It is cheap.
3) It has many bad reviews.

 

[SentinelAeon]

I am wondering, incase i dont get some good 8 ohm speakers in time, i guess i could just wire 2 and 2 4 ohm speakers in series to get 8 ohms ? That would mean half power to each speaker but if i remember correctly u said that total volume of 4 speakers will be equal to 2 speakers or even greater due to more area to produce sound ?

 

[audioguru]

The cheap low power Bluetooth amplifier is rated to drive a 4 ohm speaker on each channel so why use 8 ohm speakers that operate with half the power?
Maybe you want to use the high power 8 ohm speakers that will be used with the higher power amplifier??

Here is a You Tube video showing its cutting off and its switch problems and the seller agrees that it has those issues:

 

[SentinelAeon]

I was speaking about the big 2x25W amp when it comes to speakers. I am thinking whether ordering visaton frs 8m - 8 for about 25€ for pair, or just use the 4 ohm speakers in series i already have and first test whether it is loud enough before i go spending money

 

[SentinelAeon]

As for the little 2x6W speaker, i tested it all night on friday and it didnt turn off at maximum volume. I use 4 batteries in parallel. I did try to power it from 5V 2A microusb and there it did cutoff. The only thing i noticed is that with 2x12W speakers, at maximum volume it did distort, so basicly i had it at 90 or 95% and it was fine.

 

[audioguru]

I do not know why you talk about 4 ohm speakers in series, your amplifiers work fine driving a single 4 ohm speaker for each channel.

ANY amplifier distorts if its output level is trying to go higher than clipping. Clipping is the maximum output swing possible from the supply voltage that is used. The volume control position could be very low if the input signal level is high and the amplifier can still produce clipping. Turn down the volume until there is no clipping.

The spec's for the tiny Visaton speakers shows no bass. Will you add a bass boost circuit?
My home speakers have 8" woofers and produce a flat frequency response down to about 80Hz so I built a simple bass boost circuit with max boost of 10dB at 40hz. Then my friends asked, "Where is my new subwoofer?". Of course I needed to turn down the volume a little to eliminate clipping.

 

[SentinelAeon]

2x25W amp needs 8 ohm speakers, the little one 2x6W uses 4 ohm speakers. U said urself i will burn the big 2x25W if i use 4 ohmn speakers

 

[audioguru]

I wish you made three threads, one thread for the batteries and separate threads for each amplifier and speakers.

Post #53 is where I looked up the Banggood amplifier that uses a TDA7492 class-D bridged amplifier IC. Yes, it is not designed to drive 4 ohm speakers.
We do not know which amplifier IC is used in the 2x6W amplifier, with a 5V supply its output per channel might be 2W into 4 ohms or 1.2W into 8 ohms. The difference in loudness will be only a little.

For the 2x25W amplifier if you connect two 4 ohm speakers in series then the enclosure must be double the volume so that the little amount of bass produced is not reduced anymore.

 

[SentinelAeon]

Thank you for your answers, it will be a while before i get all the needed parts so i will use this topic for my other questions since u know your electronics.

I have liitokala 500 charger and i am very happy with it, got it for like 15 euros. 1 thing though is that it doesnt have temperature protection. I often test old lithium batteries and some have very high internal resistance and therefor heat like crazy during charging. The first time i charged them i noticed it just in time, they were already at 70C and probably would burn if i didnt notice it. Because of that i want to implement temperature protection that will beep when temperature is to high and disconect the charger.

I will use those nice little pieces that stop conducting electricity when temperature reaches 60C. But now i need a good way to include them into my charger without it being to bulky.
It would be best if i measured temperature of all 4 ground pins, since battery is connected to ground and will have basicly almost the same temperature as batteries. I wanted to connect all 4 ground pins directly to this thermostat switch. Soo here comes the question:

- can i connect all 4 ground pins to thermostat with copper wire ?

That way copper wire would quickly heat up and thermostat would reach critical temperature and shut off. But i am afraid that connecting all 4 grounds together will somehow affect charging/discharging of the charger. So, can i do this or not ?

 

[audioguru]

A fast charge at a high current produces a lot of heat. Simply select a lower charge current for less heat.
My little two-cells 280mAh Li-PO batteries are charged at 300mA and they just get a little warm. A high internal resistance reduces the charging current which reduces the heat.

 

[SentinelAeon]

I tried even at 300mA and its is same. Its mostly red batteries and while normal batteries charging at 1A never go above 30C (and i tested many batteries), those red ones even at 300mA go to 60C and above. So i really need the answer to my question: can i fuse ground pins together or will this somehow mess up charging ?

 

[audioguru]

You need to take the charger apart to see if the battery grounds are all connected together. Maybe each battery connector has a resistor to ground that measures its current.

 

[SentinelAeon]

Opening it would void the waranty. I guess i will have to implement protection some other way. I guess that heat from batteries radiate so if i put thermistor 1 cm away from battery it will still heat up enough to trigger it. I will have to measure it, maybe if i want batteries to stay under 50C, i can use 40C thermistor. I will have to measure it

 

[SentinelAeon]

I got almost all the parts i need for both my bluetooth 2x25W and my nicd to lithium drill conversion. I have to organise things now and start slowly so i guess the best part to start is checking if charging part of the speakers will be ok. I will connect batteries to BMS and to charger and see if it limits charging to 4.2V (or 4.3V anyway)