Eliminate influence of switching noise from light switch in to power supply - diyAudio
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Old 24th February 2008, 07:04 PM   #1
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Default Eliminate influence of switching noise from light switch in to power supply

Dear forum,

My problem is that I want to eliminate switching noises from light switches into my power supply - and finally to my speakers.

Initial situation:

Power Supply: (from mains 230V in, to DC out +/- 35VDC)

1.) Mains Inlet Filter Schurter FKH 4304.4003 Medicinal Version (http://www.schurter.se/pdf/german/typ_FKH.pdf)
2.) 500VA Noratel Toroid Transformer (Encapsulated Series)
3.) Two Rectifier Bridges (35 Amp. Glass Passivated Bridge Rectifier (Fagor FB 3510)
4.) Fuse
5.) Smoothing caps (2 x 47000 uF per Rail)
6.) Filtering Caps (2 x 1000uF, 2 x 100 uF 2 x 10 uf, 2 x 0.1 uF) per Rail

Problem:

I can hear switching noises thru my speakers when lights are turned of by light switch or for example also by taking of an electric iron power plug from mains and

Till now I installed a 0.1uF/630V cap in parallel after the Mains Inlet Filter and in front of the Toroid Transformer. It helped a little bit, but the switching noises are still present.

How can I eliminate those switching noises ? Any opinions ?
Where can i find a frequency spectrum of such a noise to design a filter for it ?

Thanks in advance
artQuake
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Old 24th February 2008, 08:12 PM   #2
gareth is offline gareth  Wales
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Try using a contact suppressor connected directly across the offending switches.

Thanks
Gareth
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Old 24th February 2008, 08:51 PM   #3
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Thanks for your reply,

i see, but isn't there a solution to solve this problem directly on the input of my power supply ?

Best regards
artQuake
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Old 24th February 2008, 09:09 PM   #4
Eva is offline Eva  Spain
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Don't blame the power supply. The noise contains RF that is being radiated by all mains wiring in your home and picked up by the own preamplifier and/or amplifier circuits and their interconnects.
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Old 24th February 2008, 09:32 PM   #5
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Thx Eva, but I blame it, because the switching noise is existing also when all other audio components (preamp, cdp and other) are turned off. So only the Amps (PSU) are turned on while this happens.
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Old 24th February 2008, 09:47 PM   #6
Eva is offline Eva  Spain
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Then the problem of EMI susceptibility is in the amplifier circuit.
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Old 25th February 2008, 12:13 AM   #7
gootee is offline gootee  United States
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Quote:
Originally posted by artquake
Thx Eva, but I blame it, because the switching noise is existing also when all other audio components (preamp, cdp and other) are turned off. So only the Amps (PSU) are turned on while this happens.
Do your amplifier's inputs have lowpass RF filters?
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Old 25th February 2008, 05:04 AM   #8
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Well it's a BPA200 Bridged/Parallel Circuit consisting of two LM4780 including servos. For example HERE (Page 12) In my case all Op's are non-inverted (Gain 22) while using a symmetric input. There is no DC blocking input capacitor @ the input.

Gootee there is no low pass RC filter. But why it should be one in there ?
When i can here the clicks of the light switches thru the speakers, then the noise frequency spectrum is allready in the audible frequenciy range. A filter in here, makes no sense. Or did i missunderstand it ?

Knowledge about the frequency spectrum of a switching noise would be the basic to create a Filter for it. Right ? Any FFT available ?

Best regards
artQuake
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Old 25th February 2008, 06:00 AM   #9
Eva is offline Eva  Spain
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Strong picked up RF can disturb op-amps and amplifier circuits resulting in audible noise. Low-pass filters are required on each signal input to keep ambient RF under control. Reducing the gain of op-amp circuits at RF is also recommended, particularly when there are remote potentiometers.

This "less components in the signal path result in better sound" philosophy is completely wrong. It creates noisy, unreliable and unstable circuits most of the time.
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Old 25th February 2008, 09:03 AM   #10
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Thanks Eva,

How does that LP circuit look like ?

In the Feedback:
(For Reducing the gain of op-amp circuits at RF)
Click the image to open in full size.

At the Input:
Click the image to open in full size.


Wich one do i need ? Both ? or only @ Input ? How to calculate the the values ?

Best regards
artQuake
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