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Thread Contributor: raufjayNeed help for Audio amplification from FT811

#1
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[attachment=82][attachment=82][attachment=82]Hello,
I need some help for Audio amplification from FT811 audio output.

Please see attached schematic. This is how I tried to amplify the audio from FT811. FT811 sends out audio in pwm shapes. 
The amplification is done alright, but I always hear a humming sound out from speaker. I am using 8ohm half watt speaker for it. 

Can you please advise me some good scheme so I can control that humming sound.

Thanks,

Rauf


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#2
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The sound is something very delicate in this series of screens. I have reduced background noise to minimum levels, but there is always some noise.

One of the solutions is to make a 4 order filter. read page 10 of the attached file. and the second is to feed the audio circuit from another source of power.

For example, use a ground analog and not digital, this greatly reduces the noise. For example, use a resistor between ground and ground of the audio circuit.


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.pdf   NHD-7.0-800480FT-CSXV-CTP.pdf (Size: 862.44 KB / Downloads: 5)
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#3
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Better response on post RE: Need help for Audio amplification from FT811It's a pity the sound noise problem with this chips, from my experience, I think most of the problem is due to clock jitter, the noise level is much worse with the internal oscillator.
Antoni
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#4
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Hello,
Thank you for your replies.
I have already seen that schematic as the same is mentioned in FT81x programming reference manual. I have difficulty in sourcing TPA6205 chip. Rather I have used TDA2822 instead. As shown in the attached schematic I have attached in my first post, I have adapted the same filtering system except the 74ALS125 buffer. So mine is 3 stage filter.
I will try by separating the AGND with GND.
Thanks
Rauf
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