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Pesky 120Hz Buzz / Hum From Speakers
Pesky 120Hz Buzz / Hum From Speakers
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Old 15th March 2019, 05:09 AM   #51
Evenharmonics is offline Evenharmonics  United States
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Hum breaker resistor fixed it. I didn't want to modify the board but that's what it took. I had to cut / scrape off little bit of trace on the board and solder a 12 Ohm resistor across it. No more buzz / hum! However, now I hear faint radio reception from speakers. Now onto RFI cure method...
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Old 15th March 2019, 11:01 AM   #52
scottjoplin is offline scottjoplin  Wales
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Are there RF filters on the inputs?
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Old 15th March 2019, 11:33 AM   #53
tmuikku is offline tmuikku  Finland
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Do you have proper electrical connection between all chassis panels? Sometimes paint / powedercoating prevents electrical connection between panels = poor faraday cage. How are the input wires again, shield goes to amplifier ground or chassis ground? Can't quite see from the picture if the input wires are coaxial or shielded twisted pair. If coaxial, ignore the question.

Last edited by tmuikku; 15th March 2019 at 11:39 AM.
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Old 15th March 2019, 04:27 PM   #54
Evenharmonics is offline Evenharmonics  United States
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No RF filter at the input yet. I will be installing one soon. One connection of 1nF ceramic cap between input ground bonding wire to chassis should be enough, no?

Input cables are coax shielded.
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Old 16th March 2019, 01:38 AM   #55
kct is offline kct  Canada
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Pesky 120Hz Buzz / Hum From Speakers
1nF is way too much for my taste. You'd be killing the amps frequency response. Try 100p to 220p at most. Any cable you plug on the input will add additional capacitance to that.

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Last edited by kct; 16th March 2019 at 01:49 AM.
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Old 16th March 2019, 08:08 AM   #56
Bonsai is offline Bonsai  Europe
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There are two filters that need to be installed for RFI

1. A 1-2 nF ceramic cap from the signal ground right at the input connectors to the chassis at the point of entry. The cap leads should be no more than 1 or 2 cm long - the shorter the better

2. A series mode filter Pi in line with the signal plus. I usually use 220 Ohms and 1 nF or 1 k and 220 pF. The Both work very well. The cap is returned to the signal ground and not the chassis ground. Ideally you want this also at the input connector(s) but more often than not they end up on the amp module PCB

This should kill any RFI and will have no effect on the audio signal.

Last edited by Bonsai; 16th March 2019 at 08:12 AM.
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Old 16th March 2019, 01:43 PM   #57
Evenharmonics is offline Evenharmonics  United States
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I've heard radio reception through my active speakers (Behringer Truth 82030A for desktop computer) but cured it with ferrite bead around the line level cables which is located very close to vent openings at the back cover of speaker. Can the same work in this case too? I happened to have a few spare ferrite beads.
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Old 16th March 2019, 06:09 PM   #58
Bonsai is offline Bonsai  Europe
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Yes, ferrite beads work well - that’s another weapon in the arsenal. If you have some try it. If that does t work, do step 1 and 2 mentioned earlier.
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Old 17th March 2019, 01:16 AM   #59
Evenharmonics is offline Evenharmonics  United States
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All done! No buzz / hum or radio reception.

Images are HBR and ferrite bead installed. Thank you all for the help.
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File Type: jpg HBR-installed.jpg (505.5 KB, 23 views)
File Type: jpg Ferrite Bead.JPG (610.6 KB, 24 views)
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