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Old 12th April 2010, 03:55 AM   #1
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Default tda729x amp power supply

hello everyone i have gotten much helpful tips from these forums i have searched quite a bit but haven't found any answers so here is my predicament i am building a home theater pc the pc is built using standard parts no custom stuff but the amp is going to be a 7 channel powered by tda729x (first build td94 because i bought all the parts before i realized how easy TDA7293 was to bridge/parallel) anyway sense it will all be in one case (with several fans) i am hoping to use one power supply however standard pc psu's are 12v max so is there anyway to get the required volts (40) out of a standard PSU without moding the windings

thanks in advance

P.S. the 7 channels pull about 840 watts (7*120watts = 840watts/45volts=18+/-amps {easily attainable by a 1200+/- watt psu})

thanks again for all your all your help
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Old 12th April 2010, 05:12 AM   #2
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Your power estimates are a little amiss because to put 120W into a load using a class B amplifier puts power into your heatsink too. Why do you want to use a PC power supply? I'd suggest using a pair (or maybe more) of 24V power supply modules. Where I live, a 24V 10A SMPSU brick is fairly cheap but going higher power, the cost goes up considerably.
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Old 13th April 2010, 01:04 AM   #3
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If you read the datasheet you will realize that there is no way to get 120w out of a Single chip , the heat dissapation is way to much for the chip , you might get 75w into 8 ohms .....
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Old 13th April 2010, 01:30 AM   #4
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Yeah, but two in bridged mode will do it nicely enough. And he did mention that he'd realised how easy they were to bridge/parallel.
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Old 13th April 2010, 03:31 AM   #5
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thanks for the responses the reason i wanted to use a pc psu is because this amp will be built into the same case as my home theater pc and i would prefer to use only one power supply to power both components (amp & pc) as for the power rating the design im working on will allow for future up grades and want to have enough power available without many modifications. thanks again for all the help.
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Old 13th April 2010, 04:09 AM   #6
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Quote:
Originally Posted by jeorgejetson69 View Post
the reason i wanted to use a pc psu is because this amp will be built into the same case as my home theater pc and i would prefer to use only one power supply to power both components (amp & pc) as for the power rating the design im working on will allow for future up grades and want to have enough power available without many modifications.
Yeah, but if you modify the 12V output of that power supply to give 40V, what will become of your hard disks?
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Old 13th April 2010, 10:08 PM   #7
Minion is offline Minion  Canada
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There is pretty much no way you are going to be able to use a PC PSU to Power a TDA7293 much less 7 of them !!!

You would first need to extensively Mod the PSU to get the correct Voltages but then you are going to run out of Current on the power Rails , especially on the Negitive power Rail and it would probably not be the quietest PSU either....

You could though Gut a PC PSU and Put a linear PSU (Transformer, Rectifier and Smoothing caps) in the PC PSU Case , Might have a Hard time Squeezing it all in but I"m sure it could be done ......

If you wanted to use a PC PSU you should have gotten a Class D Amp , they are more efficient and can be run off of 12v DC but I don"t like there sound personally ......


Cheers

PS: Also a 1200w PSU won"t fully power a 7+ channel amp at 800w output , The amp is Maybe 50% efficient but probably less so you would need at least twice the Power in the PSU as the Amps output ....

Last edited by Minion; 13th April 2010 at 10:13 PM.
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Old 14th April 2010, 07:20 PM   #8
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The big advantage of the TDA7293/7294 is, it can be used in class H aka class G configuration. That means you need a power supply with two rail voltages, e. g. 25 and 50 V. Such a set-up could indeed lead to 120 W output power from a single chip while maintaining the chip heatsinkable. You could also build the amps with the smaller voltage only first to check whether such martial amounts of power are really required. Remember that everything that is fun is either forbidden, unhealthy or makes fat. 840 W can be unhealthy to your hearing.

Apart from the fact that it is not feasible to supply PC and amp from the same power supply, it is also recommendable to keep those two separate. You don't want the switching noises from the digital domain to wreak havoc on the audio signals.

I remember reading somewhere (lenardaudio?) that surround mixes normally don't use all channels at full steam at the same time. So you may get away with a PS that is not capable of supplying all channels at the same time with full power.
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Old 15th April 2010, 07:12 PM   #9
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thanks for all your input after reading all the input I have received I have reconsidered the feasability of this design. there doesn't seem to be any reasonable way to accomplish my original design so I have started looking for other options including a class d amp using tda8920however the negative 12v supply usually caries only a few amps at best 2 separate power supplies is not feasable with the amount of space availabe and a torroid cabable of powering the amp is quite costly from everyhing I have found as far as using a pc psu with large enough filter caps feeding the rails I don't believe switching noise woult be a problem, correct me if I'm wrong, especially with a class d such as tda8920.thanks againfor your input
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