TDA8947J output power@12 volt supply

sudhir kumar · 2011-08-30 10:54 am

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

sudhir kumar · 2011-08-30 11:05 am

some photos of my amp,(taken from net,but i have the same kit).

AndrewT · 2011-08-30 1:53 pm

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?

sudhir kumar · 2011-09-02 6:14 am

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.

pacificblue · 2011-09-02 5:27 pm

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.

sudhir kumar · 2011-09-05 6:18 am

pacificblue said:
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

johnr66 · 2011-09-05 5:45 pm

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.

sudhir kumar · 2011-09-06 6:24 am

johnr66 said:
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????????

AndrewT · 2011-09-06 12:08 pm

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.

johnr66 · 2011-09-06 2:12 pm

sudhir kumar said:
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.

AndrewT said:
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!

sudhir kumar · 2011-09-07 6:51 am

To Andrew T & Johnr66
if it is so then why people are interested in so powerful car ams(called as 1000watts)?
I india i have seen many local made car stereos(inside is sanyo old la4440) and for my ears it gives very powerful sound.

johnr66 · 2011-09-07 12:55 pm

sudhir kumar said:
To Andrew T & Johnr66
if it is so then why people are interested in so powerful car ams(called as 1000watts)?
I india i have seen many local made car stereos(inside is sanyo old la4440) and for my ears it gives very powerful sound.

More watts is more SPL. 1000 watts is ~18db more than 15 watts. Of course it's likely the amp can't produce anything near 1000 watts, but is probably more powerful than a 15 watt BTL chip.

17 years ago, I built a 2 channel amp with a couple BTL chips to drive a DVC 12" driver in a ported box. Clean power would have been about 27 watts. It was plenty adequate for the job.

pacificblue · 2011-09-07 6:25 pm

sudhir kumar said:
why people are interested in so powerful car ams(called as 1000watts)?

Depends on the people. Some want so much power, because they believe the salespeople that tell them it's the way to go.

Others want 1000 Watts to impress their friends, without the slightest idea what the difference is between a 10 W amp and a 100 W other than the figure. Those are the usual victims that buy 2x17 Wrms amps for 20 Euros and believe the 2x1000 W PMPO print on the case is a proof of superior quality.

A few people that compete in sound-offs, need that much power to achieve 130dB+ of clean output from 20 Hz to 20 kHz to be able to win SPL competitions.

From a technical point of view you "need" that much power to drive extreme-long-throw woofers with 150 g or more of moving mass, built into too small enclosures, and playing music with significant content below 50 Hz at ear-shattering level. You may also need that amount of power, if you are a fan of big church organs and wish to listen to their lowest notes at live levels in your home.

90 % of all listeners will find that somewhere between 10 and 50 W they have all the power they ever need for home audio. A few difficult speakers may ask for more, but then it is worth considering different speakers rather than more powerful amps.

sudhir kumar · 2011-09-29 12:13 pm

I have read in the foroum that TDA1554 is better than old LA4440 but both datasheet tell that @10%THD.If the THD figure is same why one chip is better than other?

johnr66 · 2011-09-29 1:51 pm

sudhir kumar said:
I have read in the foroum that TDA1554 is better than old LA4440 but both datasheet tell that @10%THD.If the THD figure is same why one chip is better than other?

The TDA1554 is a newer IC with much less support components needed. Ignore the stupid 10% figure. That is well into clipping. These chips will do in the 12 to 15 watt range of clean power before clipping with a 14.5 volt supply. Check the THD vs frequency and THD vs power graphs if provided.

sudhir kumar · 2011-09-30 6:16 am

johnr66 said:
The TDA1554 is a newer IC with much less support components needed. Ignore the stupid 10% figure. That is well into clipping. These chips will do in the 12 to 15 watt range of clean power before clipping with a 14.5 volt supply. Check the THD vs frequency and THD vs power graphs if provided.

Thanks for reply,
but some more questions
If i have two chip amps (suppose one based on TDA8947) and another (basesed on tda1554) , if i supply them with equal voltages(14.5) and put equal load(4 ohm).will there be a difference in output power ?I think my english is not good but perhaps you are getting my point.
thanks in advance.

johnr66 · 2011-09-30 12:59 pm

sudhir kumar said:
Thanks for reply,
but some more questions
If i have two chip amps (suppose one based on TDA8947) and another (basesed on tda1554) , if i supply them with equal voltages(14.5) and put equal load(4 ohm).will there be a difference in output power ?I think my english is not good but perhaps you are getting my point.
thanks in advance.

Your English seems fine to me. With the same Vs and load, the output power will be the same. In a practical test, there may be slight differences as chips can vary from lot to lot, but the difference would likely be within a watt. Since it takes 2x the power to make a perceptible change in sound (3db), you could never tell the difference.

sudhir kumar · 2011-10-03 6:55 am

to johnr66,
Thank you very much for reply.It was a practical problem for me but now solved.Actually i have a ready built tda8947 kit and i wanted to use it as a car-amp but not sure about its o/p at car battery voltage so i decided to make a tda1554q.since you told that both will give approx same o/p with above conditions so i am going to use the same tda8947 kit in the car.
thank again for reply.

Pjfred · 2014-02-26 12:28 pm

Can someone send me a diagram on a btl design for tda8947?

TDA8947J output power@12 volt supply

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