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Old 6th January 2014, 05:22 AM   #1
arifs is offline arifs  Pakistan
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Default LM4766 Strange Sound

Hi,
I have built an amplifier based on LM4766 IC. Everything is good but the audio output seems distorted. Tried reducing volume with volume knob, but the distortion was still there so i guess it rules out the limited current from power supply issue (which i dont suspect)

I played around with it and figured out that if i remove the 22uf feedback capacitor the volume gets very slow but the distortion goes away.

I asked one of my engineer friend. He recommended that i play with increasing the capacitor value (instead of removing it), as it will reduce distortion.

Is it the right approach. Can it be due to faulty IC ?
Will be thankful on any help on the issue.
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Old 6th January 2014, 08:54 AM   #2
Mihkus is online now Mihkus  Estonia
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Input resistor that goes to gnd value ?
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Old 6th January 2014, 09:14 AM   #3
Mooly is offline Mooly  United Kingdom
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Is this built as a two channel amp or as a bridged amp ? I would perhaps suspect instability. You really need to look at this with a scope to see what is going on. Layout is critical with any high gain chip like this. Correct wiring practice and grounding needs to be followed.
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Old 7th January 2014, 04:38 AM   #4
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Yeah, if the 22uF is Ci from the datasheet removing it puts the part in unity gain, which is unstable. Given the opposite seems to be the case I'm tempted to guess wiring error. But without at least a schematic and layout pic it's hard to say anything meaningful.
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Old 7th January 2014, 04:00 PM   #5
arifs is offline arifs  Pakistan
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Thanks for all responses, I played more with circuit as I figured more gain = more distortion after doing some test. So i make it this way added a potentiometer between the shunt capacitor and 1k resistor and adjusted it to a sweat spot where i can get most power with less distortion. (top left capacitor and resistor in bottom image)

http://www.chinabaike.com/uploads/al...16403340-0.jpg

I was reading some more on internet and found one article saying that distortion can be caused by lack of power amplifier needs. mine in 24+24 V 5Ampere Transformer (LM4766 is 80 watt IC) and i have added 6000uf filtering capacitor.
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Old 30th January 2014, 05:57 AM   #6
arifs is offline arifs  Pakistan
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Hi,

I found the problem. It was faulty IC . Though i did managed to assemble another board and able to set gain around 30.
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Old 30th January 2014, 06:13 PM   #7
Mooly is offline Mooly  United Kingdom
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Thanks for the update. Great to hear you found the problem and fixed it.
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