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subwoofer isolation transformer possible hum reducer...?

Boston Chris

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Given that the powered subwoofer hum requires RCA connection with the amplifier, and powering both the subwoofer and the integrated amplifier from the same multiple outlet, heavy duty extension cord has no effect on the hum, is a subwoofer isolation transformer still a possibility for hum reduction/elimination?

Details: 60Hz or 120Hz hum in Klipsch 10-SW powered subwoofer connected to Line Magnetic 210IA integrated amplifier (no external preamp in system).

Power cord on subwoofer is: (1) two pronged at male end and (2) hardwired at subwoofer end.

Thank you!

  1. Hum frequency : Could be piano B2 (~ 120 Hz) or Piano B1 (~60 Hz) – very hard to discriminate
  2. With no subwoofer RCA input : No hum
  3. Add subwoofer RCA input from Line Magnetic amplifier : hum
  4. Change Line Magnetic amplifier volume setting : No effect on hum
  5. Change Line Magnetic amplifier source selector : No effect on hum
  6. Disconnect all Line Magnetic amplifier RCA inputs : No effect on hum
  7. Power Line Magnetic amplifier and subwoofer amplifier into same extension cord : No effect on hum
  8. Multiple Repositioning - amplifier to subwoofer RCA interconnects position with respect to all power chords : No effect on hum
  9. Change amplifier to subwoofer RCA interconnect cables : No effect on hum
 

AdamG247

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Given that the powered subwoofer hum requires RCA connection with the amplifier, and powering both the subwoofer and the integrated amplifier from the same multiple outlet, heavy duty extension cord has no effect on the hum, is a subwoofer isolation transformer still a possibility for hum reduction/elimination?

Details: 60Hz or 120Hz hum in Klipsch 10-SW powered subwoofer connected to Line Magnetic 210IA integrated amplifier (no external preamp in system).

Power cord on subwoofer is: (1) two pronged at male end and (2) hardwired at subwoofer end.

Thank you!

  1. Hum frequency : Could be piano B2 (~ 120 Hz) or Piano B1 (~60 Hz) – very hard to discriminate
  2. With no subwoofer RCA input : No hum
  3. Add subwoofer RCA input from Line Magnetic amplifier : hum
  4. Change Line Magnetic amplifier volume setting : No effect on hum
  5. Change Line Magnetic amplifier source selector : No effect on hum
  6. Disconnect all Line Magnetic amplifier RCA inputs : No effect on hum
  7. Power Line Magnetic amplifier and subwoofer amplifier into same extension cord : No effect on hum
  8. Multiple Repositioning - amplifier to subwoofer RCA interconnects position with respect to all power chords : No effect on hum
  9. Change amplifier to subwoofer RCA interconnect cables : No effect on hum
Welcome Aboard @Boston Chris.
 

solderdude

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Try:

1: subwoofer with RCA cable but not connected to amp.
2: subwoofer with RCA cable and the RCA cable at the amp shorted with aluminium foil so pin and shield are connected.
3: same as 2 but now hold the RCA connector with aluminium foil against the shield of the RCA out of the amplifier.

Are 1 and 2 without hum and 3 with hum then you have a ground loop.
 
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Boston Chris

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Try:

1: subwoofer with RCA cable but not connected to amp.
2: subwoofer with RCA cable and the RCA cable at the amp shorted with aluminium foil so pin and shield are connected.
3: same as 2 but now hold the RCA connector with aluminium foil against the shield of the RCA out of the amplifier.

Are 1 and 2 without hum and 3 with hum then you have a ground loop.


Try:

1: subwoofer with RCA cable but not connected to amp. NO HUM
2: subwoofer with RCA cable and the RCA cable at the amp shorted with aluminium foil so pin and shield are connected. NO HUM
3: same as 2 but now hold the RCA connector with aluminium foil against the shield of the RCA out of the amplifier. NO HUM

Are 1 and 2 without hum and 3 with hum then you have a ground loop.

Given NO HUM results from theses tests, and no hum reduction when Line Magnetic amplifier and subwoofer are powered from the same multi-outlet extension cord, it seems most likely the hum is not from a ground loop, but a frequency coming from the Line Magnetic amplifier. Is that fair to say? Thank you!
 

solderdude

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I would think so yes...
 
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Boston Chris

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I would think so yes...

Well, to be fair, I can only (barely) hear the hum when the subwoofer amplifier is turned up all the way, there is no input into Line Magnetic amp, and I’m kneeling with my ear 6 inches from the subwoofer driver.

So maybe I’ll just stop doing that, stop looking for any ground loops, and listen to some music. :). Thanks so much for your help!
 

solderdude

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When you can't hear hum under 'normal' conditions in your listening position I would leave it alone.
There are lots of folks that hear noise from their tweeters with the ears against it and not from 0.5m away and are still worried about it.
Below hearing threshold is below hearing threshold.

Hint. Set the system up as it would normally be used. Enjoy a quiet evening and before you head off to bed listen carefully (no music) is you hear noise/hum and if it disappears when gear is switched off. When not it is below your hearing threshold and you're fine.
 
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