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Old 12th July 2012, 04:53 PM   #1
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Default Class D or TD Amplifier Noise

Hi;
Its been some time since I made the pyro boxs with the help of the great guys on this forum.

I was woundering If anyone has seen any problums with switching amps putting out higher than audible noise that may interfear with other equpment. Like RS232 or RS485 Serial communication.
Andy
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Old 13th July 2012, 11:21 AM   #2
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Anyone have any input?
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Old 13th July 2012, 01:01 PM   #3
DF96 is offline DF96  England
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Quote:
higher than audible noise
Higher in power or higher in frequency? I assume you mean the latter. A switching amp should have a filter to stop RF getting out (harmonics of the switching frequency). On the other hand, RS232 comms should use decent cable and receivers to stop RF getting in.
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Old 13th July 2012, 01:33 PM   #4
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Quote:
Originally Posted by 4pyros View Post
I was woundering If anyone has seen any problums with switching amps putting out higher than audible noise that may interfear with other equpment. Like RS232 or RS485 Serial communication.
Andy
You can't just generalize it by topology like that.

Of course it's capable of causing interference, but whether it does or not comes down to circuit design, pcb layout, and final implementation.
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Old 13th July 2012, 01:43 PM   #5
DF96 is offline DF96  England
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There are some "topology" issues. Class D does generate interference, but a good filter will stop it getting out. Class A does not; Class B should not.
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Old 13th July 2012, 03:19 PM   #6
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I meant you can't just ask... Class-D noise - Yes/No?

There are too many variables involved.
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Old 13th July 2012, 03:35 PM   #7
DF96 is offline DF96  England
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Agreed, but the OP is simply asking if anyone has had problems with Class D and serial comms. This is a fair question, even if the answer turns out to be No. There is a mechanism which could conceivably cause such problems - a faulty or missing output filter.
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Old 14th July 2012, 12:04 PM   #8
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Yes; I asked if anyone had seen communication problems around switching amps.
I could see a filter cap drying up and reducing the efficancy of the low pass filter on the output.
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Old 14th July 2012, 01:54 PM   #9
DF96 is offline DF96  England
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Unlikely to be 'drying up' as the filter caps would probably have solid dry dielectrics. However caps can fail or grounding wires come loose. A 'scope on the output would soon tell you.
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Old 14th July 2012, 06:24 PM   #10
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The amps were from a sound company and I can't cheak them.
But if it is posible for these things to spew out interfering noise than I should try and protect the comms lines.
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