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Old 5th January 2006, 11:39 AM   #1
Chaom1 is offline Chaom1  Estonia
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Default problem with tda7294

Hello

I have a little problem with my 2xtda7294 amplifier i just made.
I have to give it input at least 2-3v to get output 20v.

Maximum output i have got is 21v, then the input was 3.5v

So I dont know what is the problem - it should give 30v with 1v input at least. My power sypply is +-32v.

The schematic I used is here: http://www.masterkit.ru/main/set.php?num=540
http://www.masterkit.ru/info/magshow.php?num=48

Of course there is a possibility to lower the r1 (680ohm) to lets say 200 ohm and then rise c3 from 22mkf to 100mkf to save the bass responce. But I kinda dont wanna do that, something must be incorrect about this circuit.

Maybe someone can help me.

thanks in advance
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Old 5th January 2006, 11:56 AM   #2
moamps is offline moamps  Croatia
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Default Re: problem with tda7294

Quote:
Originally posted by Chaom1
[B]Maximum output i have got is 21v, then the input was 3.5v
Hi,
did you check the waveform at the output?
How did you measured the in and output voltage?
Quote:
So I dont know what is the problem - it should give 30v with 1v input at least. My power sypply is +-32v.
Yes. But for 30VRMS at the output, you need almost +/- 50V voltage from your power supply.
What's the output voltage for 0.5V at the input?

Regards,
Milan
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Old 5th January 2006, 12:12 PM   #3
Chaom1 is offline Chaom1  Estonia
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I didnt check the waveform
In and output voltage I measured with usual tester. Output had 6.8ohm 5w resistor in water.

with 0.5v input it has output something 5-7v
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Old 5th January 2006, 12:21 PM   #4
Chaom1 is offline Chaom1  Estonia
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but in datasheet there is also capactor there, and in every circuit in the web. If I remove it, i will loose low frequency, the links says. And i have stereo amp and different 100pf capacitors, so one of two should be working great anyway.

but both of the channels act the same...
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Old 5th January 2006, 12:33 PM   #5
lineup is offline lineup  Sweden
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What frequency did you use?

Many AC voltmeters can not show good numbers at 1000 Hz
If you do not have a special AC voltmeter,
try using 200 Hz or something like this.
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Old 5th January 2006, 02:35 PM   #6
Chaom1 is offline Chaom1  Estonia
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I used my soundcard and later old fm-radio.
Well, im certain that something is wrong since i havent seen an amplifier before what plays 1/3 of its power with my soundcard.

the output is about 700mv.

later the radio output was already 2-3v
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Old 6th January 2006, 03:37 AM   #7
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remove arrowed cap in the image im posting.
its not there in standard schematic.

+

dont rely on dmm.for as lineup says,dmm response is poor for high frequencies.
Attached Images
File Type: jpg remove the arrowed c2.jpg (16.1 KB, 213 views)
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Old 6th January 2006, 12:33 PM   #8
Chaom1 is offline Chaom1  Estonia
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thanks, gonna try it.
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