Diy stereo bluetooth portable speaker help

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Hello everyone, I recently had made a small mono powered portable bluetooth speaker/amp.

I found a tda1515bq, looks up the datasheet,
Found the parts, and built it.
The schematic is in the datasheet. TDA1515BQ datasheet - 24 W BTL or 2 X 12 W Stereo Car Radio Power Amplifier

I am using a bluetooth receiver for the audio in.
I'm using a 12v battery to the input and 2 20watt four ohm speakers. at low volumes the amplifier works with little distortion. At high volumes it has great distortion issues, especially lower notes, like the bass.

I was wondering if the Lipo battery can't supply enough current, or do I need a pre amp after the bluetooth reciever?
Any help is appreciated. Thanks
 
Just so the Reader gets some more info, I measured the current drawn from the battery and it is about 300mA at a low volume.

Also, when I say distortion, the speaker make an unpleasant thumping noise when the bass notes are prominent. But the higher tones are alight. At higher volumes, the bass notes are drown out by the irratable thumps and humming, almost like a low screech. But at this volume the higher tones suffer from regular distortion/noise.

I have tried my iPod and tablet with a cord as an audio input and it seems even worse. Like the screech is louder and more prominent.
 
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Just how big is this 12V Lipo battery? You are probably looking at a requirement of several amp-hours capacity. If the amplifier draws 300 mA average current at low volume, that's 3.6 amp-hours for say, 12 hours operation - before you even turn up the volume! Be aware that the current you measure with a DMM may not be correct as the meter likely won't respond correctly to the Audio frequency current imposed on the DC current drawn, even with large reservoir capacitors in the amplifier. I assume you didn't fit caps as the app notes refer to auto amplifiers, where current isn't a problem. With no signal though, the chip should not draw much more than the spec. 75mA.

You need a substantial battery but even something like this will have limited play time before it needs recharging, based on your measurement. It would be a pain to recharge often, unless your listening was at moderate level and only for an hour or two per day.

Is the battery in good condition? (they do go bad and deliver less power over time) You may need to check that it can deliver enough current to drive the amplifier and speakers adequately after a full recharge. The chip is rated to supply 7W/ch to 4 ohm speakers with a 14.4V supply, so it isn't a powerhouse and it will probably rate around 60% efficiency overall, meaning you need about 2A peak current capacity for stereo with a 12V supply. Sound will dwindle and distort well before the battery fully discharges though, perhaps as you experience now.
 
Aside from Ian's observations, my main concern is the power amp to load compatibility :confused:
You can connect two ( same) speakers in two ways : series or parallel
When Z halves ( parallel ) the 2 Ω is rather low.
For a BTL amplifier the load must be doubled ( respect to the capability of each channel to handle power ) to stay within safety limits.

I'd say the good ol' single coil is the best solution. Try ONE 8Ω speaker and see how the current request diminuishes as the ability to make clean sound
 
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It would be helpful if you could say how big, how many mAH or AH your battery is capable of storing. That is where the answer will be if the battery is too small.

If you plan to run the amplifier from say, a 1-3A wall-wart to test it, which should be possible, you will need a large electrolytic capacitor from the power + connector to ground, to smooth the DC supply and maintain a steady current source to prevent the supply dropping sharply when there is heavy passage like bass. I suggest a 4,700uF 16V or preferably 25V rating if you have a conventional transformer (heavy type). If yours is a switching power supply (lightweight, no transformer) a cap won't help much.

If you have a vehicle with a 12 V battery, use that as the best source of power, via the cigarette lighter socket or direct from the battery to power your amplifier for testing. If the bad distortion persists, you have a wiring issue or perhaps you didn't fit a heatsink which will cause those problems when the thermal protection kicks in and out rapidly as the chip heats and shuts down, cools and restarts.

Car radios that used these chips, usually just had it clipped to the steel chassis, sandwiched to an aluminium cover plate or bracket and so you don't need a big heatsink for 2 x 6W/4 ohms. The recommended rating for use in a hot auto is about 10 degrees K per Watt but you may not need so much in a home environment. Technical background here: How to Select a Suitable Heat Sink
Example of similar, larger chipamp and suitable heatsink for use with natural convection: Aliexpress.com : Buy TDA7297 2X15W Audio Amplifier Board AMPLIFIER Big HEAT SINK \ Wima capacitor from Reliable capacitor 25v suppliers on ELE FM transmitter | Alibaba Group
 
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An SLA battery is just fine. At 2.5 AH however, that one won't last long between charges but there are much bigger ones. This looks like a fair compromise of cost/convenience: Panasonic 12V 7.2Ah Sealed Lead Acid Battery ;. 'Best to keep recharging after each use with a specialised SLA battery conditioner rather than flatten it, much as a car battery. You can buy them or DIY the best ones here: Sla Battery Charger Note this reply on Parts Express's website which tries to present the issues -
Sealed lead acid batteries will have a limit to the number of times it can be charged. This is the reason that accessory batteries for marine use are called deep cycle. it allows for more discharge/recharge cycles and a deeper discharge overall. A fully charged should be about 12.6 volts. and not drop below 8 volts under a load.
All the same, a full 2.5 AH type should work fine for several hours. Measure the terminal voltage of your present battery and see what it is before, during and after use and make your own decision about its state of charge when the distortion occurs. It may not be good when in use but without knowing how big the battery is, and what sort of charger you are using, we can only guess about the distorted sound. A pic or 2 of your set-up might explain all. :)
 
Here is the lipo battery I am testing with, except mine is a 1100mAh version. Its a very small battery, and not meant to be used in the amplifier, but I was just trying to find something that will let me test everything.
https://www.parrotshopping.com/us/p_parrot_product.aspx?i=250956

I tried a 12v nicd drill battery with the same outcome. https://www.directtoolsoutlet.com/brands/ryobi/130164001

I dont know if this has anything to do with the problem but I have a 3.5mm jack wired in for the input of the amp. When nothing is plugged into the jack and turn the amp on, the speakers make a hiss, screech, crackle. When I plug the bluetooth recieiver
Wireless Bluetooth Receiver with 3.5mm Output and Microphone
Into the audio jack, the noise stops. This is how it is if I plug any device into the audio input.

Im away from the project now, so I will try a car battery asap.
 
So the two .1 uf cermaic caps that i have connected to the 4.7ohm resistor on both channels are not reading .1uf. but instead they arent reading anything, my multimeter just switches between uf and mf but never gives me a value. the code on the caps are 104 which is .1uf.
??
im going to replace those two caps and see what happens.
 
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So I tried different audio inputs with different power sources and still the same result, a loud screech. Its gotta be a wiring problem, but ive checked multiple times.

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I have a feeling this might give someone a clue out there with what is wrong. If I dont have anything plugged into the audio in jack, then it makes a noise where it starts out in a low frequency and works its way up to a high frequency and repeats itself over and over again. A thought that I had is it sounds like a capacitor charging, understand?
maybe that info might help debug this.
*****
 
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