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Diy stereo bluetooth portable speaker help
Diy stereo bluetooth portable speaker help
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Old 22nd June 2015, 04:10 AM   #1
dbutler6259 is offline dbutler6259  United States
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Default Diy stereo bluetooth portable speaker help

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
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Old 22nd June 2015, 05:16 AM   #2
dbutler6259 is offline dbutler6259  United States
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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.

Last edited by dbutler6259; 22nd June 2015 at 05:20 AM.
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Old 22nd June 2015, 11:34 AM   #3
Ian Finch is offline Ian Finch  Australia
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Diy stereo bluetooth portable speaker help
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.
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Old 22nd June 2015, 12:18 PM   #4
picowallspeaker is offline picowallspeaker  Italy
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Aside from Ian's observations, my main concern is the power amp to load compatibility
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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Old 22nd June 2015, 01:34 PM   #5
dbutler6259 is offline dbutler6259  United States
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The battery is almost brand new, I am going to try and find a 12v power supply rated for a couple amps and then see what kind of sound it outputs.
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Old 22nd June 2015, 01:38 PM   #6
dbutler6259 is offline dbutler6259  United States
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If I need to get a bigger battery I will get one, I just wanna make sue that the battery is the problem.
Once I figure out the problem I will try to fix it with any means necessary.
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Old 22nd June 2015, 05:56 PM   #7
picowallspeaker is offline picowallspeaker  Italy
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The amplifier-to-load matching is the first thing to take in consideration
Just simple math by dividing and summing
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Old 22nd June 2015, 06:01 PM   #8
dbutler6259 is offline dbutler6259  United States
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So what is wrong with the 2 four ohm speakers?
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Old 22nd June 2015, 07:10 PM   #9
Ian Finch is offline Ian Finch  Australia
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Diy stereo bluetooth portable speaker help
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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Old 22nd June 2015, 08:05 PM   #10
Ian Finch is offline Ian Finch  Australia
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Diy stereo bluetooth portable speaker help
Quote:
Originally Posted by dbutler6259 View Post
So what is wrong with the 2 four ohm speakers?
4 ohm speakers are fine as a stereo pair, as all car speakers have been forever. Picowallspeaker might be thinking, things would get nasty if the amplifier was wired in bridged mode and the speakers wired in parallel for higher power in mono. I don't think that would be a good idea.
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