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Old 15th March 2011, 11:00 AM   #1
Hosam is offline Hosam  Syria
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Smile Question about TDA7294 in bridge

as I know the bridge mod as the data sheet the pin 2 from the first TDA chip connect with the pin 14 in the second one to make the bridge work. then my question if I want to make serial connection with 4x bridge TDA can I do this:
make as data sheet 2x connected with each other pin2 with pin14 then from the first TDA pin 14 connect to pin 2 to the third TDA and from third TDA pin 2 connected again with pin 14 of the fourth TDA does this work if I did it if not well why if you please explain the problem?
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Old 16th March 2011, 07:26 PM   #2
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That won't work. A BTL configuration uses one amp that amplifies the non-inverted signal and one amp that amplifies the inverted signal. At the output they add up to nearly double the voltage. If you try to invert the signals again, the third amp in your example would amplify the same signal as the first and the fourth would amplify the same signal as the second. There is no further voltage gain in it.
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Old 16th March 2011, 11:35 PM   #3
Hosam is offline Hosam  Syria
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wow I get now the idea thank you very much to help understand it in such simple words, but also you open my eyes to another question sorry if I ask again ...
then if the the gain come from the voltage can I use another type of amp to produce more signal gain after the inverted output? I mean for example use simple chip that accept the inverted signal then amplified it again as I read in opamp.
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Old 17th March 2011, 05:52 PM   #4
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I assume that by 'more signal gain' you mean higher output power.
In theory you can add another amplifier after a chipamp. In practice you won't find many chipamps that can deliver significantly more output power, so there won't be any real gain. You would have to use transistors to amplify the output signal further. At that point you have to ask yourself, if it is not better to build a transistor amp in the first place, maybe with a driver IC to reduce complexity.
Is there a reason why you want more power than a bridged TDA7294 can deliver? 150 W into 8 Ohm is already a lot.
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Old 18th March 2011, 09:31 AM   #5
Hosam is offline Hosam  Syria
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Quote:
Originally Posted by pacificblue View Post
I assume that by 'more signal gain' you mean higher output power.
In theory you can add another amplifier after a chipamp. In practice you won't find many chipamps that can deliver significantly more output power, so there won't be any real gain. You would have to use transistors to amplify the output signal further. At that point you have to ask yourself, if it is not better to build a transistor amp in the first place, maybe with a driver IC to reduce complexity.
Is there a reason why you want more power than a bridged TDA7294 can deliver? 150 W into 8 Ohm is already a lot.
my idea behind signal gain is to produce more clear sound with acceptable power I know you could suggest filters well no I want to use as base then use another filter to get good gain as you mention transistor is good example.
in the other hand build transistor amp is an option but not for this chip its another project I want to do later, in calculation the bridge mode I have give 170w after test I know its very good power but not clear enough and it has noise at full load in all ranges the speakers I use with test 2x 4ohm 480W8inch TS-A6872R at bridge mod.
lets back to the main idea I really want to thank you for the information above. but do you have any idea how to make this amp better in sound at full load or how to improve it to be more clear like double filter?
building on working project is better than start with new one just for note of why I want to use this way.
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Old 18th March 2011, 12:12 PM   #6
AndrewT is offline AndrewT  Scotland
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build it right = sounds better.

Adapting screwed techniques is virtually guaranteed to = sounds worse.
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Old 18th March 2011, 02:53 PM   #7
Hosam is offline Hosam  Syria
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I build it correct and right but still something missing why I could say that well because if I compared it with my old stereo PIONEER private S-Z92V speakers and deck system that was 120w/6ohm then the sound is way to get close. anyway I consider this bad comparing cause I don't know what was the technology used inside that system but I still convinced it not the power mention at all.
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Old 18th March 2011, 03:03 PM   #8
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Hosam View Post
I build it correct and right but still something missing
need I say more !
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Old 18th March 2011, 07:37 PM   #9
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Quote:
Originally Posted by Hosam View Post
the speakers I use with test 2x 4ohm 480W8inch TS-A6872R at bridge mod.
are not compatible with
Quote:
from TDA7294 datasheet page 13
In this application, the value of the load must not be lower than 8 Ohm for dissipation and current capability reasons.
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Old 18th March 2011, 10:39 PM   #10
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I think he wired the speakers in series. I doubt the TDA7294 would take 2 ohms in bridged mode for any meaningful period of time - heck, it barely takes 6 ohms (see logitech).
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