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Old 12th April 2012, 11:40 AM   #1
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Arrow Reduce Output Noise and International SNR standard

Hello Everybody,
We are developing an Audio system with integrated Power supply (SMPS), which results to noise (hum). Can anybody suggest any advanced method to reduce as i have applied Filters (EMI and output). Also give the International Acceptable No-Signal to Noise Ratio.
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Old 12th April 2012, 11:50 AM   #2
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I don't know of an international SNR standard. The relevant standards apply to interference with other devices. There's no standard that regulates how quiet or noisy your product must be.
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
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Old 12th April 2012, 12:31 PM   #3
Mooly is online now Mooly  United Kingdom
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An SMPS shouldn't cause "hum" any more than a normal linear supply. Hum is low frequency components entering the audio chain so all the normal rules apply about tracing and determining the cause.
A simulation free zone. Design it, build it, test it.
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Old 12th April 2012, 12:53 PM   #4
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I agree with previous posters on their points. A "noisy" SMPS will usually result in all sorts of hash and spikes on the output and can take quite a bit of things to get rid of it. Good shielding - good grounds - and some good caps and a choke or two for starts. If you have a "hum" it is most likely lousy grounding - or perhaps ground loops or a crappy power trany. That's where I would be looking 1st.

As to SNR - well the higher the better but there is no "standard" to meet regarding audio gear. If you want a target to shoot for then aim for -130 or better as that will limit the noise floor for the rest of the rig.
DIY audio can be expensive but getting to see things go up in smoke - that's priceless!!!! ..... "whatever - call it brainfart of Mighty ZM"
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Old 12th April 2012, 05:37 PM   #5
DF96 is offline DF96  England
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My guess is that you don't need "advanced" methods to reduce noise and hum; just good circuit design by someone who knows what he is doing, and then proper implementation (e.g. don't let the PCB designer ruin a good circuit).
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Old 13th April 2012, 11:45 AM   #6
AndrewT is online now AndrewT  Scotland
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Originally Posted by DF96 View Post
don't let the PCB designer ruin a good circuit
I love you, oops, I mean I like your quotes.
regards Andrew T.
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Old 13th April 2012, 02:42 PM   #7
godfrey is offline godfrey  South Africa
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This reminds me of this thread, which also involves a couple of guys developing a commercial product and needing help with the design. Maybe the same project?
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Old 13th April 2012, 04:21 PM   #8
DF96 is offline DF96  England
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Maybe someone developing a commercial product using free help on here (if that is what is happening) ought to be encouraged to offer a percentage of sales to support the forum. Or a discount to forum members, as Jan does for his magazine.
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Old 14th April 2012, 04:12 AM   #9
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Originally Posted by adityaonline View Post
Also give the International Acceptable No-Signal to Noise Ratio.
What do you want? The no-signal to noise?
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Old 17th April 2012, 10:24 AM   #10
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Thanks Everybody, well its not a commercial project as we are making it for some futuristic product. Noise is a big problem, and most of the circuitry used to suppress it. I think, it has some ground problem and power supply output's low frequency amplification problem too.
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