Subwoofer hummmmmm

Running a Vandersteen 2Wq sub, connected to a NAD 375 Bee integrated amp. The sub is plugged into its own electric socket. Vandersteen recommends it be kept on all the time. When the amp is turned on, no problem. When the amp is turned off, the sub emits a low hum. All thoughts, suggestions welcome.
Why not call Vandersteen and get it from the designer's mouth?
Mr. V. usually calls back the next day.
Dedicated lines fixed hum problems in my system.
I did message RIchard V. He did respond very quickly. Suggested I leave both the NAD and the 2Wq on all the time. Said both would last longer if I did so. The obvious and quick fix. I was just curious as to why it hums.
I am glad to hear Mr. V contacted you quickly. He really provides great service.
As far as the hum goes, it may be your electrical wiring. Something isn't grounding properly.
Perhaps Almarg will chime in. He knows more about such things than I.
Much more...
One thing for everyone to consider...Only after taking the appropriate safety precautions, open your house electrical service box and check all of the grounds.  In other words, tighten all of the grounds that may not be sufficiently grounded.  I did this years ago after discovering that when I touched the clothes dryer, it hummed.  Sure enough, a couple circuit grounds were not well secured. Tightening those connections brought about an immediate cure of that problem.

I don't know if this will help with the issue at hand, but it is a good thing to check.  Floating grounds does not a good audio system make!
Bob (Gdnrbob), thank you kindly.

What the OP has described isn’t surprising. The 2Wq has a very high input impedance, described as being more than 100K. When the amp that is driving it is turned off the high impedance input is left in an essentially uncontrolled state, referred to by EE’s as a "floating" state, but with the ground connection to the amp still being present. That amounts to an invitation to hum problems.
The sub is plugged into its own electric socket.
If practical, it might be worth trying plugging the sub and the amp into the same outlet. Assuming that doesn’t help, though, and if you’d prefer to not keep both components turned on all the time, what I suspect will help is as follows:

Purchase two resistors having a resistance of approximately 1500 ohms or so (the exact value isn’t critical; anything between about 1000 and 2000 ohms should be suitable), and a power rating of at least 2 watts (that rating assumes the resistance is at least 1000 ohms, and takes into account the power capability of your NAD 375BEE). Connect one resistor between the + and - terminals of the sub’s input for one channel, and the other resistor between the + and - terminals of the sub’s input for the other channel.

You may be able to find suitable resistors at Radio Shack, or if not you can order them from an industrial electronics distributor such as (which has no minimum order requirement or handling fee),, or

The quality of the resistors is not critical, and I would not expect them to have any impact on sonics.

-- Al

What did I say?