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7070A hum in the HT + Audio usage

kosta88, modified 5 Years ago.

7070A hum in the HT + Audio usage

Youngling Posts: 1 Join Date: 8/12/16 Recent Posts

I am trying to use only one subwoofer in the following combo-setup:
- Active system (usually for computer use, sound production, gaming, etc)
- Home-Theater setup

As an Active System there are two 1031A, connected as usual to front IN L/R. Always worked fine.
Soundcard is a Focusrite Forte.

HT-Setup is a Marantz SR7009, which, up until now, had a 2nd subwoofer.
I connected that sub to SUM/LFE-IN, and that worked out fine. I have a good sound, no hum, nothing from the HT-Setup.

Now the two systems are in the same room, and I would like to use only one subwoofer - my 7070A.

Connecting both systems to the sub causes the sub to hum - BUT: not when computer is "idle".
Usually only when I open a game, only then, there is a hum.
The hum is also not present if either speakers or home-theater is not connected.
And: it is independable from the mute/volume setting on the Forte.

The cable connecting the HT and the sub is a high-quality cinch cable, and on the subwoofer-side there's an adapter from Amazon... however, I also have a "self-made" cable, which I soldered, setting pin 2 to signal (inner cinch) and pin 1/3 to ground (outer ring on cinch) - same hum, nothing different.

So to shorten it:
If both genelecs and HT are connected there is a hum - only when some (3D) game is running.
If I disconnect (or power down) Forte, there is no hum.

I am quite at the end of my wits, as this is no ordinary 50Hz hum.

Ideas, suggestions, where to start troubleshooting?

Best regards,

After some searching, I found out I might try using a DI-Box. However, I do question this approach. Because, why does the noise happen when I use a game, and doesn't happen when I don't... what do you think?
ilkka-rissanen, modified 5 Years ago.

Re: 7070A hum in the HT + Audio usage

Yoda Posts: 2564 Join Date: 3/23/09 Recent Posts

In general it is not advisable to connect multiple sources to same subwoofer, this can cause ground loop problems and noise.

I am not sure if I understand this sentence: "I connected that sub to SUM/LFE-IN, and that worked out fine." Can you explain more?

Unfortunately I don't have any idea why the hum is only present during games.