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Old 30th August 2011, 09:54 AM   #1
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Default TDA8947J output power@12 volt supply

hi friends,
i have a power amplifier kit based on tda8947j.Now i want to use it as car amplifier.This kit is working in btl mode.Kindly tell me that what will be its output power at the load of 4ohm load on the power supply of 12-14volt(single supply).Kindly see the attached datasheet.
thanks
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File Type: pdf TDA8947J_2.pdf (187.3 KB, 130 views)
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Old 30th August 2011, 10:05 AM   #2
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some photos of my amp,(taken from net,but i have the same kit).
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File Type: jpg amp2.jpg (38.2 KB, 258 views)
File Type: jpg amp3.jpg (44.2 KB, 253 views)
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Old 30th August 2011, 12:53 PM   #3
AndrewT is offline AndrewT  Scotland
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Consider each half of the BTL alone.
Vcc = 12Vdc
Max AC output voltage ~ Vcc / 3, i.e. 4Vac.

Now consider the BTL mode.
This allows double the voltage to be driven into the 4r0 load.
Let's get you to substitute values into the standard P=V^2/Rload formula.
Determine the Vpk and Ipk into a resistor load. Can the amplifier meet these demands?
Determine the instantaneous Ipk into a reactive speaker load. I suggest you allow three times the resistive load current.
Can the amplifier meet this current demand?
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Old 2nd September 2011, 05:14 AM   #4
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to Andrew T
Thanks for reply,
Considering Vcc 14 volt dc the o/p is nearly 21.5 watts and for Vcc 12volt it is nearly 16watts.This chip can drive 8ohm load in btl mode at Vcc 18Volt so i think it can drive 4ohms@Vcc12volt if adequate heatsinking is provided.Kindly give me some more info about this.
thanks.
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Old 2nd September 2011, 04:27 PM   #5
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Figure 5 in the datasheet confirms that the amplifier can work into a 4 Ohm load in BTL mode from up to 22 V rails. The graph indicates ~14 W from 12 V and ~20 W from 14 V.
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Old 5th September 2011, 05:18 AM   #6
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Quote:
Originally Posted by pacificblue View Post
Figure 5 in the datasheet confirms that the amplifier can work into a 4 Ohm load in BTL mode from up to 22 V rails. The graph indicates ~14 W from 12 V and ~20 W from 14 V.
Thanks for pointing out the fact
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Old 5th September 2011, 04:45 PM   #7
johnr66 is offline johnr66  United States
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Those graphs are for 10% distortion which is ridiculous in my opinion. I like to test amplifiers for maximum clean power just before clipping to get a better feel of its capabilities. I checked a few BTL ICs designed for car audio use. These are designed for maximum output swing due to the relatively low supply voltage. At 14 volts supply, you get 13 to 14 watts of clean power into 4 ohms.
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Old 6th September 2011, 05:24 AM   #8
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Quote:
Originally Posted by johnr66 View Post
Those graphs are for 10% distortion which is ridiculous in my opinion. I like to test amplifiers for maximum clean power just before clipping to get a better feel of its capabilities. I checked a few BTL ICs designed for car audio use. These are designed for maximum output swing due to the relatively low supply voltage. At 14 volts supply, you get 13 to 14 watts of clean power into 4 ohms.
I think that if it is clean 14 watts X 4,it will be enough for listening in car????????
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Old 6th September 2011, 11:08 AM   #9
AndrewT is offline AndrewT  Scotland
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I've listened to many standard and upgraded and a few custom in car sound systems.
Most would sound far better @ 0W of power output rather than the exaggerated claims made for many worse than useless components.
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Old 6th September 2011, 01:12 PM   #10
johnr66 is offline johnr66  United States
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Quote:
Originally Posted by sudhir kumar View Post
I think that if it is clean 14 watts X 4,it will be enough for listening in car????????
Almost certainly it will. Just for fun once, I took a fairly efficient ported sub I designed with WinISD (12" driver, 2.8 Cu. ft. cab, F3@30Hz) powered with a small chip amp and 9volt battery (~1 watt of clean power at 8 Ohms). With cabin gain, the amount of bass produced was many times more than the head unit (stereo BTL amps) and the pioneer 6x8 door speakers. So, it really it depends on the speakers. Of course, most cars don't have the room for proper efficient bass cabs x 4.

Quote:
Originally Posted by AndrewT View Post
I've listened to many standard and upgraded and a few custom in car sound systems.
Most would sound far better @ 0W of power output rather than the exaggerated claims made for many worse than useless components.
Looking at car head units, many are rated 50watts x 4. I downloaded a manual from a Pioneer unit to see the specs. It said:
50 watts x 4
25 watts x 4 RMS power
15 watts x 4 RMS power into 4 Ohms with 1% distortion (CEA2006 compliant rating)

So, the advertised rating was over 3 times what I would call the accurate rating. I would probably rate it at 12 to 13 watts for a lower distortion figure.

Then there are these one note wonder bass cabs. Ever seen a 12" driver stuffed in a .7 cu. ft. ported box? At least it fit in the trunk!
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