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Old 4th May 2004, 05:30 PM   #1
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Question Stupid question about voltage and output power

I am planning to build two TDA7293 bridge amps. In the datasheet is written that output power of bridge is 150W (THD 10%) on 8 ohm speaker and with +/- 25V power supply.

According to the datasheet one chip can give 80W RMS (1%THD) on 4 ohm speaker with +/- 29V supply.
If in bridge every chip sees half of speaker impedance I guess I could buid +/- 29V supply for my bridge amp and get 160W on 8 ohms (1% THD) or 200W (10%THD). Than every chip would "see" 4ohms.

The main question is: Will my amp clip before with +/-29V supply, or it will just produce more more power and heat ?

Thanks !
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Old 4th May 2004, 10:33 PM   #2
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I think you are making some mistake..

You say that this chip is geting more power on 8 Om Speaker , than on a 4Om speaker?And the voltage for the second is higher..?

This is not 100% right.Normaly amps working at 8Om are giving more output power wen 4Om speakers are connected.In this case the amp is geting more hungry for input power and it heats up more.So normly in this case you have to lower your voltage to keep the output power in some normal levels or it is posible to destroy the IC..



So if you put a 8 Om speaker in bridged mode on this chip the output power will be bigger than 300W(10% THD) If you put a higher voltage the output power will grow even more.All this risks your IC.Bether lower the supply voltage and you will see no problems

Good Luck
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Old 4th May 2004, 11:28 PM   #3
mAJORD is offline mAJORD  Australia
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going back ot the start of your post.. I see a problem with the claim of 150watt into a single 8ohm load , with +-25v supply

do thee chips have some sort of DC-DC converter?
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Old 5th May 2004, 01:59 AM   #4
s2kov is offline s2kov  Canada
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How will i increase power of my GC but still using 8 ohm impedance?
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Old 5th May 2004, 05:40 AM   #5
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Quote:
You say that this chip is geting more power on 8 Om Speaker , than on a 4Om speaker?And the voltage for the second is higher..?
This chip can give 100W (10%THD) on 4ohms with +/-29V supply, or 100W (10%THD) on 8 ohms with +/- 40V supply.

You can download the datasheet of TDA 7293here

The bridge mode with this chip is better explained in datasheet of TDA 7294 (older version of the same chip).
http://www.st.com/stonline/books/pdf/docs/1057.pdf


Ihave recently build amp with this same chip with +/- 32V supply and it is driving 4 ohm speakers perfectly without too much heat. Now, if I put two of this chips in bridge with +/- 29V supply I think I could drive 8 ohm speaker with no problem. Every chip would act as it is working on single 4 ohm speaker and would give 100W which is normal to this chip.
Hmm, maybe I'm missing something here. Please correct me !


Quote:
So if you put a 8 Om speaker in bridged mode on this chip the output power will be bigger than 300W(10% THD)
300W??? How ? Can you please explain it better ?

Quote:
If you put a higher voltage the output power will grow even more.All this risks your IC.Bether lower the supply voltage and you will see no problems
It's not like I'm trying to connect this chips on +/- 40V or more (it can stand 120V).
Heatsinking is no problem to me.

Quote:
going back ot the start of your post.. I see a problem with the claim of 150watt into a single 8ohm load , with +-25v supply
Please see the datasheet !
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Old 5th May 2004, 11:40 AM   #6
mAJORD is offline mAJORD  Australia
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i dont have the datasheet!

can u link to it? or at least the mfg webpage , philips??
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Old 5th May 2004, 12:22 PM   #7
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Quote:
Originally posted by mAJORD
i dont have the datasheet!

can u link to it? or at least the mfg webpage , philips??
See the post just before your own!
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Old 6th May 2004, 11:33 AM   #8
mAJORD is offline mAJORD  Australia
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haha im sorry , totally didnt see that.

and i understand now... bridge mode. so its really swinging +- 50

Still cant answer your main question , having trouble getting my head around it

Will try again tomorrow
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