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I have some triac dimmer from IKEA (bought several years ago).
This dimmer makes audible noise (hum or buzz), very notable during night when it is placed on a bedside table. I failed to find the culprit.

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I reverse engineered this circuit. This is the schematic:
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I tried this:

  1. Firstly I have accused the inductor (L1 in my schematic) that it is vibrating. So I glued it with hot glue. Didn't help. Then I shorted it with a wire (that inductor is not really necessary for dimming). This didn't help either. The noise was still there. So I ruled this inductor out.
  2. Next I accused the ceramic cap (C3). I replaced it with film capacitor. Didn't help.
  3. Next I accused triac (Q1) and its heatsink (it is sort of flimsy, could be vibrating). I removed this triac completely and put new BT137-600E there (I have built several dimmers with this triac, never noticed any noise). This didn't help either. So I ruled out triac and its heatsink.
  4. I was desperate at this point. Next I accused capacitor C1. I removed it (it is just for filtering). Didn't help. So I ruled out this cap.
  5. Next I accused capacitor C2. I have replaced it by another film capacitor, and the noise is still there.

Did I miss anything? How to figure out what is making this annoying hum (or buzz) noise?

UPDATE:
I'm using it with incandescent lamp. I tried different ones.
My dimmer (I created) doesn't make any noise with none of those lamps. The noise is definitely going from dimmer itself, not the filament of the bulb.

The noise is loudest when dimmer is about in the midpoint (around half brightness), it is quieter when brightness is at the maximum, and quietest when brightness is at the minimum.

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  • \$\begingroup\$ Is it a hum or more likely a buzz? Does the noise vary with the dimming. Often they will buzz more at intermediate or low dim levels where there are rapid changes in voltage as the triac turns on. At full brightness the voltage across the circuit is low when the triac turns on. \$\endgroup\$ – Kevin White Jun 8 at 18:32
  • \$\begingroup\$ The load can buzz also, are you sure it isn't the load? I have incandescent bulbs that buzz at certain phase angles. The harmonics cause the filaments to vibrate. \$\endgroup\$ – Mattman944 Jun 8 at 18:43
  • \$\begingroup\$ @KevinWhite Well, I do not know the difference between hum and buzz. It sounds like a mosquito with lower frequency. I updated my question. Loudness of that noise changes with level of dimming. It is loudest aproximatelly in the middle (around 50% brightness). \$\endgroup\$ – Chupacabras Jun 8 at 19:07
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    \$\begingroup\$ I doubt hot glue can mute 50 Hz noise, because cooled down hot glue is far from stiff and 50 Hz is quite low. You could try to test the inductor by placing the PCB and inductor on some damping material and next put the inductor on a resonance box (eg a wooden table) while the PCB is still on this damping material to find out if you can really rule out the inductor. \$\endgroup\$ – Huisman Jun 8 at 21:10
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    \$\begingroup\$ @SunnyskyguyEE75 Sorry for late response. Thanks for the tip. I have ordered some cheap electret microphones from china (the reason for my delay) and built some amplifier for it. I'll put findings to an answer. \$\endgroup\$ – Chupacabras Jul 7 at 21:21
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I have used some electret microphone (with amplifier) to localize the source of that buzzing. Thanks to Sunnyskyguy EE75 for the this tip.
Well, I found not one but several parts that were making the buzz :(

  1. inductor L1
  2. ceramic capacitor C3
  3. trimmer RV1
  4. trimmer RV2 (the main trimmer for brightness)

Possibly some others, but these were the loudest.

Unfortunately this is beyond economical repair.

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  • \$\begingroup\$ Vibration maybe conducted to all the parts, but the big ceramics are the most likely piezo agitators. Changing to a dimmable LED will be much quieter. \$\endgroup\$ – Sunnyskyguy EE75 Jul 7 at 23:58
  • \$\begingroup\$ @SunnyskyguyEE75 yes, that was I my thoughts too. But as I wrote in my question, I already tried to change that cap for film capacitor and the buzzing was still there. \$\endgroup\$ – Chupacabras Jul 8 at 7:22
  • \$\begingroup\$ Sounds very normal unfortunately. \$\endgroup\$ – winny Jul 8 at 7:35

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