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Old 29th November 2004, 09:25 PM   #1
CPX is offline CPX  Romania
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Smile Problem with bridged tda7294

Hello.I have used the schematic provided with the tda7294 amp and build the bridged version.The amplifier works but the bass sounds bad ..i hear something that sounds like the center channel of a poorly encoded mp3 file around 80-130 hz...but the input signal is good( i verified it..the problem is not here) only the bass is affected by this problem...but this is bad since i intend to use the amplifier for a subwoofer aplication.If you have any iddea where the problem is please respond.Thanks
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Old 30th November 2004, 11:37 AM   #2
Markje is offline Markje  Netherlands
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Are you sure you are well within the max current it can deliver, you're power supply can deliver and maximum dissipation of the TDA? And that is not clipping?

Greetz Mark
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Old 30th November 2004, 06:27 PM   #3
CPX is offline CPX  Romania
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yes..the distorsion is hearable at all volumes,the amplifier is not cliping...the problem is elsewhere....i wonder if it is the boot strap capacitor althought there are those in the diagram...i just discovert i used 0.44 uf for dc decoupling instead of 0.56 but i dont thing there is the problem...i will try today the other pair of tda7294 wich is in stereo configuration not in bridged...i.m still searching...thanks
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Old 30th November 2004, 09:48 PM   #4
CPX is offline CPX  Romania
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the stereo configuration sounds bad tooi realy dont have any iddea.i use 2 transformers as a power supli..each transformer handles half of voltage....the transformers are identical,output is at +-35 volts..the transformers have about 80w each...maybe this helps....i tested with 3 speakers...same problem...i will try to use biger bootstrap capacitors.......please help thanks
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Old 1st December 2004, 09:16 AM   #5
Markje is offline Markje  Netherlands
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When you use them parallel, you're bootstrap capacitor should be N*22uF, where N is the number of TDA's, so in you're case, 44uF (2*22uF parallel). When you bridge them, you use each boottrap seperately, one TDA works inverted, the other one workes non-inverted (only problem is that the gain has to be exzct teh same). The schematics in the data sheet is parallel.

I'm haven't tried parallel or bridging myself yet, I just finished the single chip version and I still have to test it (hopefully this weekend). I based my version on the schematics I found here. Only adjustment: 22uF bootstrap capacitor and not 66uF (I still have to design/calculate the larger version).

There is another interesting document, but I can't find it right now. I found it googling for tda7293. It's the manual of 'Endstufe A100', I have it at home, but I dont know if it is still on the internet somewhere. I'm home late tonight, so if I don't forget, I'll try and upload it, or send it to you tomorrow. There is information in it about how to bridge and parallel use the TDA. On this version I want to base the larger version (parallel/bridge, depending on the needed output power).


I'll see if I can find it later today, I have a meeting in a few minutes.

Greetz mark
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Old 1st December 2004, 10:26 AM   #6
Markje is offline Markje  Netherlands
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Can't find it. I'll see if I can upload the file for you when I'm at home.

Greetz Mark
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Old 1st December 2004, 08:03 PM   #7
Markje is offline Markje  Netherlands
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It's 1.5MB so I cant upload it... sorry. I'll see if I can find another way to get it to you.

Greetz Mark
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Old 2nd December 2004, 03:15 PM   #8
CPX is offline CPX  Romania
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Thank you very much for oyur replies Mark I will study the schematics you provided...anyway i made some expriments myself (changing some capacitors) and i discovert the problem was not realy in the amplier...i only changed tge dc decoupling capacitors from input from 0.44 mf to 1.0 mf.the problem seems to be in the end the very input signal that i tought it was perfect...i retested today with another output from my sound card(center asnd subwoofer ) and with the output from the cd rom unit.it sounds better... i will verify again when i will buid the active low pass filter..but i will not do this yet...i am busy ... i thank you for your interest and i wish you good luck in your project as well...
PS: if you find anything interesting related to this ic class(tda729X) or anything else dont hesitate te post or reply..10x
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Old 30th December 2004, 03:07 PM   #9
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Default bridged tda7294

salut
pt. tipu din Cluj
bai tu de unde vrei bass daca folosesti un transf de 80w , cat aveai acolo 2.5A ? pt. tda 7294 ? fii serios !
tre sa ai vreo 10 A ca sa mearga treaba cu tda 7294 si cum zici ca ii folosesti si in punte mai ales , nu e de glumit
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Old 31st December 2004, 11:08 AM   #10
CPX is offline CPX  Romania
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Multumesc de raspuns bogdane Problema am rezolvato de mult....de fapt nu era nci o problema...era de la semnalul de intrare...si folosesc 2 transformatoare de 80 W deci exact cat trebuie..oricum suna rau la orice volum deci nu alimentarea era problema...multumesc oricum si spor la treaba iti doresc
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