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I have a new Sonos Amp and a SVS subwoofer hum problem that I can't diagnose.

1. When the Sonos Amp is UNPLUGGED and the mains outs are unplugged and only the sub out on the Sonos Amp is connected to the SVS sub, there's a hum. The hum is louder than when the Sonos Amp is plugged into the wall.

2. When I unplug the Sonos amp and turn off the sub amp, then turn on the sub amp and plug in the Sonos amp, humming starts after a few seconds—before the white light on the Sonos amp stops blinking.

3. There is no hum When the sub is plugged into the receiver.

4. When the sub RCA isn't plugged into anything, there is no hum.

5. I've tried plugging both the Sonos amp and the sub into the same outlet. They're still humming.

6. I've tried new high-end shielded cables from SVS. Still humming.

7. I've tried on a different SVS sub. Still humming.

8. I've tried a ground loop isolator. Still humming.

8. I've tried plugging the Sonos amp into a different circuit 100' away from the sub outlet, but it's still humming.

What else can I try?

Does the hum level vary with power plug orientation in the power socket? (Experiment with flipping each unit systematically.)

While I’m not suggesting that you attempt to listen to music with the following: Connect AMP’s subwoofer output as an input to the receiver. Do you have hum? Now connect the subwoofer to the receiver. Do you have hum?

Is anything connected to AMP’s Line-In or HDMI?

 

I had the same issue with a powered Definitive Technology (DefTech) sub that I purchased in 2008 when I used wired separates (left/center/right/surrounds x 2) with a Sony ES receiver/amp. I found that the impedance between the Sonos Amp and the DefTech sub were unmatchable (incompatible). The technologies were too far apart in design. On the other hand the DefTech Tower speakers I purchased along with the sub work perfectly with the Sonos Amp.

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