A/V Help (Subwoofer Hum)

[Superhero 9017]

I have a relatively old receiver (NO HDMI INPUTS, ZERO, NADA, ZILCH!) that I use solely for music. I have a pair of bookshelf speakers and a subwoofer connected to said receiver.

• The receiver sends signal into the subwoofer via speaker wires into SPEAKER LEVEL IN (top left in pic below).
• The receiver and subwoofer share the same Power Source A.

I recently got a soundbar (Yamaha YAS-108) that doesn't come with its own subwoofer, but has a RCA subwoofer output.

• The soundbar sends signal into the subwoofer via a shielded RCA cable plugged into LINE IN / SUB IN.
• The soundbar is plugged into to Power Source B.

 

The plan was to use the subwoofer for both music and soundbar and save a few bucks. However, when both signal sources are connected (but no signal), there is an annoying hum. Unplug one source or the other, and the hum disappears.

Is there a way to get both signal sources to work together? Is it a power source issues? Help!

 

[jimmyjazz 47137]

Sounds like a ground loop of some kind.  Is everything plugged into the same circuit?  

[Robin Masters 122]

I know you're saying music only but is one of your music sources cable tv digital channels? I had this same thing happen long ago when I switched from satellite to cable. There was some 60 cycle hum introduced by the cable system, that my subwoofer would woof. The answer was some little coaxial plug adapter.

"Dayton Audio VIT-1 Isolation Transformer"

 

[mdmost 43969]

Any unshielded wires that might be touching?

[Superhero 9017]

5 hours ago, jimmyjazz said:

Sounds like a ground loop of some kind.  Is everything plugged into the same circuit?  

No. The receiver, sub, CD player and a tiny receiver are in one outlet. The TV, soundbar and AppleTV are plugged into another outlet.

I plugged the subwoofer into the same outlet as the soundbar via extension cord, but I’m gonna try plugging the receiver into the same outlet as well.

3 hours ago, Robin Masters said:

I know you're saying music only but is one of your music sources cable tv digital channels? I had this same thing happen long ago when I switched from satellite to cable. There was some 60 cycle hum introduced by the cable system, that my subwoofer would woof. The answer was some little coaxial plug adapter.

"Dayton Audio VIT-1 Isolation Transformer"

The music source is an iPad mini streaming via Bluetooth into the Bluetooth receiver (Amazon Basics). Only signal plugged directly into the receiver is the CD player. I bought a cheap ground loop Isolator between the soundbar and sub, but it didn’t help at all.

2 hours ago, mdmost said:

Any unshielded wires that might be touching?

Nope. The RCA cable runs alongside speaker wires and optical cable until it gets close to the sub, at which it point it gets close to the sub power cable. 

 

[edit] The RCA cable is shielded.

Edited December 18, 2018 by Superhero

[jimmyjazz 47137]

4 minutes ago, Superhero said:

No. The receiver, sub, CD player and a tiny receiver are in one outlet. The TV, soundbar and AppleTV are plugged into another outlet.

I plugged the subwoofer into the same outlet as the soundbar via extension cord, but I’m gonna try plugging the receiver into the same outlet as well.

Yeah, get them all on the same circuit and see if it clears things up.  (To be fair, those 2 outlets could be on the same circuit.  Flip breakers to check, if you're brave.)

[Chewbacca 7829]

Could also be a bad amp in the sub.  I need to replace the amp in my HT subwoofer.  

[RamjetFDO 10648]

This really belongs in the "Wives and the stupid things..." thread, but awhile back, I noticed an audible rattle through my system whenever the volume would be loud enough.  Of course, I immediately suspected wires, connections, blown speakers, etc.

Nope.

Huge-ass Yankee Candle sitting decoratively on a decorative plate, placed decoratively on top of my sub-woofer ... 

... decoratively causing that rattle.

[52-80 19377]

1 hour ago, RamjetFDO said:

This really belongs in the "Wives and the stupid things..." thread, but awhile back, I noticed an audible rattle through my system whenever the volume would be loud enough.  Of course, I immediately suspected wires, connections, blown speakers, etc.

Nope.

Huge-ass Yankee Candle sitting decoratively on a decorative plate, placed decoratively on top of my sub-woofer ... 

... decoratively causing that rattle.

Why would you place your decorative candles on your wife's audio equipment ?

[Superhero 9017]

13 hours ago, jimmyjazz said:

Yeah, get them all on the same circuit and see if it clears things up.  (To be fair, those 2 outlets could be on the same circuit.  Flip breakers to check, if you're brave.)

I tried what you suggested and put all the equipment into the same outlet. At first it worked GREAT, very little humming and didn't affect the tone at all. Then I spent some time organizing the signal cables/wires (but was still on the same outlet) and the humming came back with a vengeance.

I'm going to put everything onto one circuit again (as soon as Amazon delivers a shorter extension cord), run the subwoofer through a ground loop isolator and cross my fingers. 

[jimmyjazz 47137]

Did you try a different RCA cable from the sound bar to the sub? 
 

I guess it's possible the subwoofer doesn't like both types of inputs connected simultaneously, but it's a little weird that it worked until you moved cables around.