Well i Blow up a Speaker in TDA7492P! Need Help

mrsmokeof

Member
2019-10-07 2:14 pm
Hello guys,


I recently build a speaker with the TDA7492P amplifier, i used this speakers MTX TR40C they are 4Ohm. They worked great for 2 days with a power supply of 15v 3.5a borrowed from a friend , today i bought a 19v 4.72a laptop AC , when i plugged the ac to the amplifier and push a bit for the volume i saw a bit of smoke from one of the speakers and now is dead. I was using 21db configuration in the amplifier board.


I tried to search a lot on the web but cant find any answer for this and im a total noob on this things. The speakers went for warranty and im afraid i will burn again the speaker when they arrive.


Can someone help me here pls? Will be much appreciate.


(Sorry for bad english guys :/ )
 

bullittstang

Member
Paid Member
2013-05-09 2:14 pm
Ft. Worth, TX
A little bit of a guess - but how loud are you playing this amp? Actual rating is 20 watts at 1% distortion at 6-ohms. The datasheet shows 6 and 8 ohm tests and 6-ohm at 18V. It also states that over-current will step-in at 4.2A - granted you should not pull this amp load playing music, at a normal volume.

You might be clipping the amplifier signal, which will quickly burn the voice-coil of the speaker, especially a small woofer.

You might try a higher gain and see if that helps you leave the volume lower and keep the amp out of clipping.
 

TBTL

Member
2013-10-08 12:26 pm
Does the amplifier still work? A perfect amplifier in bridge tied load mode, at a supply voltage of 19 V, can deliver 45 Wrms at 4 ohms, with a peak current of 4.75 A. Class D amplifiers come pretty close.
 
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Hi


sorry to read this..


your speakers were maybe too closed to the amplifiers max. power!!

at this page i found your speakers- its rated at 40W rms power.

MTXTR40C
so lets say its continuous power if you push the volume up to the max. additionally you get a lot of distortion at this power by the amp itself---> more stress to the speakers.
but at the datasheet of the TDA7294P you will see a lot of diagrams with 8R or 6R load and at 19V power supply you easily come to the max of the chip! - 4R is not special recommended - i found just at at figure 20 a hint for the output filter for a 4R load(right buttom corner)




so try on if the amp is still working on a old speaker or a load resistor first.
if you need more power then use the red board TDA7498E or TPA3116 up to 24V


chris
 

mrsmokeof

Member
2019-10-07 2:14 pm
first thank you all,


- Amplifier still works great, after the speaker burn i pluged the 15v ac and the other speaker was playing fine.


- My box is 15cmx30cm (like this Imgur: The magic of the Internet)



- I push volume to 75 80% almost all times.



- I can select between 21db, 27db, 31db and 33db when my speaker burned i was at 27db.


So am i pushing to much from the amplifier at 19v 4.72a with this speakers? Should i use a lower voltage AC like the 15v? I have a 9v 550ma ac too. The amplifier support between 8 and 24v.


Sorry for noobish total amateur at this :/
 
Hi


do not excuse yourself...we are here to learn and have fun..;):D
As i see at the pic you have 2 speakers. so for every channel 1 speaker? hopefully yes ?...otherwise you have a 2 ohm load !!!:eek:


my proposal is to set the gain to 21 db & do not psu the volume up to the max...;)with this amp and speakers configuration. if you really want to do party all the time you have to think about a other speaker / amp configuration.



chris
 
Hi,
It is rare that speakers burn such that you have smoke coming from the coil. Evidently, if you use the full power of an amplifier that can deliver much more than the speaker can handle it is possible. In your case the 19V DC (please) is hardly the reason alone for the accident though the 19V DC allows more amplifier power.
What may have happened and what I have seen more examples of is what I will call a "coil-strike", meaning that the speaker coil has hit the magnet in the narrow gap where the coil is moving. This is possible if the speaker is overloaded in the way that the diaphragm (and speaker coil) has moved outside of what is intended. I believe Chris calls it the non-linear range. When the diaphragm moves so far out (or in), the coil may start having a non-axial movement in the narrow magnet gap on top of the axial movement. This non-axial movement may cause the coil to hit the magnet and some coil windings may get loose and then prevent free movement of the coil. When the coil cannot move well, it is poorly cooled and may overheat. This is what may have happened.

You use rather small speakers (4 Inch) and you tell us you play loud. A guess from my side is that the music you listen to includes dominant deep bass. If you have ever seen how much a speaker of 4 Inch with a strong magnet moves in and out in order to try to reproduce low bass, you will understand how easily it moves into the non-linear range. Unless you notice that the speaker starts having problems reproducing the sound without distortion (difficult to hear when you play loud) and reduce the power to the speaker, you risk a "coil-strike" etc.

4 Inch speakers cannot reproduce much bass below 100Hz. For reproduction of low frequency bass, you either need size of the diaphragm or length of stroke. The possible stroke-length is limited whatever you do in design of a traditional electrodynamic speaker.
Therefore, loud and deep bass requires a big bass speaker (10-12 Inch). With your 4 Inch speakers, you have to listen carefully when signs of distortion appear and reduce the power level a little.
In conclusion, my guess is that you burned one speaker because you tried to make it reproduce low bass which it by nature cannot reproduce at good sound level. The explanation cannot be found in simple comparison of amplifier power with nominal speaker power. Be careful when you get the repaired speaker back!
 
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mrsmokeof

Member
2019-10-07 2:14 pm
Hi,
It is rare that speakers burn such that you have smoke coming from the coil. Evidently, if you use the full power of an amplifier that can deliver much more than the speaker can handle it is possible. In your case the 19V DC (please) is hardly the reason alone for the accident though the 19V DC allows more amplifier power.
What may have happened and what I have seen more examples of is what I will call a "coil-strike", meaning that the speaker coil has hit the magnet in the narrow gap where the coil is moving. This is possible if the speaker is overloaded in the way that the diaphragm (and speaker coil) has moved outside of what is intended. I believe Chris calls it the non-linear range. When the diaphragm moves so far out (or in), the coil may start having a non-axial movement in the narrow magnet gap on top of the axial movement. This non-axial movement may cause the coil to hit the magnet and some coil windings may get loose and then prevent free movement of the coil. When the coil cannot move well, it is poorly cooled and may overheat. This is what may have happened.

You use rather small speakers (4 Inch) and you tell us you play loud. A guess from my side is that the music you listen to includes dominant deep bass. If you have ever seen how much a speaker of 4 Inch with a strong magnet moves in and out in order to try to reproduce low bass, you will understand how easily it moves into the non-linear range. Unless you notice that the speaker starts having problems reproducing the sound without distortion (difficult to hear when you play loud) and reduce the power to the speaker, you risk a "coil-strike" etc.

4 Inch speakers cannot reproduce much bass below 100Hz. For reproduction of low frequency bass, you either need size of the diaphragm or length of stroke. The possible stroke-length is limited whatever you do in design of a traditional electrodynamic speaker.
Therefore, loud and deep bass requires a big bass speaker (10-12 Inch). With your 4 Inch speakers, you have to listen carefully when signs of distortion appear and reduce the power level a little.
In conclusion, my guess is that you burned one speaker because you tried to make it reproduce low bass which it by nature cannot reproduce at good sound level. The explanation cannot be found in simple comparison of amplifier power with nominal speaker power. Be careful when you get the repaired speaker back!


Dammm, you got it right.. i really listen to deep bass and speaker move a lot up and down. Thank you for the detailed explanation and i will have more carefull when the speaker comes back.



Great community we have here :D
 
If it is concluded that the amplifier channel that destroyed your speaker is functioning well, as you said previously, has no important DC error and you actually try to play music with deep bass on your 4 inch speakers, it could be an idea to put 100Hz high-pass filters on the input of the amplifier. Such will reduce the attempt of the speakers to reproduce low frequencies it anyway cannot reproduce and reduce the stroke of coil importantly.