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Old 22nd August 2013, 01:14 PM   #1
danny92 is offline danny92  Portugal
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Default LA4450 and TDA2822M interfering

Hi everyone,

I'm having problems with two amplifiers (LA4450 and TDA2822M), they are both mounted on a breadboard because I can't make the PCB now, I can only make it in September, they both are mounted like suggested in the respective application notes. The only differences are that the two amplifiers have two 10 kohm potentiometers connected to the same stereo source. If I set one of the input potentiometers to 0 (gnd), the amplifier with this setting reproduces a distorted sound, if the other one is working (set to a position different from 0 (gnd)), if both amplifiers are working, they both reproduce a distorted sound.

What is causing this problem?
It seems that the amplifiers are making the ground path voltage float (the signal is being injected into gnd path), but this can be normal because the circuit is mounted on a breadboard or the problem has another cause?

Best regards,
Daniel Almeida
Attached Files
File Type: pdf LA4450.PDF (218.3 KB, 19 views)
File Type: pdf TDA2822M.pdf (364.1 KB, 7 views)
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Old 22nd August 2013, 01:30 PM   #2
Mihkus is offline Mihkus  Estonia
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You better make sure everything is correct, the potentsiometer might be faulty...
But i had similar problem with TEA2025 in bridge, it just went full retard.
When supply voltage was over 9V it started motorboating and if lower it distorted
Like class B amplifier with bias being very low.
Problem was solved by replacing the chip. Chip was faulty.
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Old 22nd August 2013, 01:37 PM   #3
danny92 is offline danny92  Portugal
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Thank you very much for your help,
This problem seems different, I think that the problem is in the ground path, high impedance ground path I think, breadboard paths are thin and long and can act as inductances at AC, the TDA2822M was replaced and the problem remains.

Best regards,
Daniel Almeida
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Old 22nd August 2013, 04:16 PM   #4
danny92 is offline danny92  Portugal
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Signal GND and Power GND should have different paths to the supply capacitor?

Best regards,
Daniel Almeida
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Old 23rd August 2013, 07:18 PM   #5
danny92 is offline danny92  Portugal
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Yes, that solved the problem.
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