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Class D Switching Power Amplifiers and Power D/A conversion

Well i Blow up a Speaker in TDA7492P! Need Help
Well i Blow up a Speaker in TDA7492P! Need Help
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Old 7th October 2019, 07:15 PM   #11
chermann is offline chermann  Austria
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Join Date: Jan 2017
Location: Vienna
Oh yes....Eva is right!!


check with her advice the DC voltage at the output.
if you have not an DMM at home !
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Old 7th October 2019, 07:33 PM   #12
mrsmokeof is offline mrsmokeof
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Join Date: Oct 2019
ty eva for the free tip will try it.
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Old 7th October 2019, 08:07 PM   #13
FauxFrench is online now FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
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!

Last edited by FauxFrench; 7th October 2019 at 08:17 PM.
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Old 7th October 2019, 08:47 PM   #14
mrsmokeof is offline mrsmokeof
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Join Date: Oct 2019
Quote:
Originally Posted by FauxFrench View Post
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.



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Old 7th October 2019, 09:04 PM   #15
FauxFrench is online now FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
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.
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