Subwoofer hum problem

[auujay]

The setup is a Creek Audio A50iR amp with Ascend Acoustic CBM-170 speakers (left/right) and a Hsu Research VTF-2 sub. The amp does not have a subwoofer out so the wires (14 gauge I believe) run from the amp's speaker outputs to the sub's high level inputs and from the speaker outs to each left and right speaker. I think the distance from the amp to the sub is probobly about 12 feet.

The problem is that there is a 60Hz hum (I assume it is 60, it is constant non the less) when the florencent light in the next room is turned on. I know a 60 Hz hum sounds like a ground loop problem but I am not sure because it is only happens when the light is on. My current theory is that the speaker cable running from the amp to the sub is acting like an antenna but I don't know of an easy way to test or solve this problem..

I know that GLIs are one solution for ground loops but I have heard they compromise the sound quality (and I a not even sure if this is actually a ground loop).

[wid]

Disconnect the speaker wires and see if the sub still hums.If it does then you
know it's not the speaker wire.

[Retread]

If I understand the scenario, you are using the sub's amp, but are feeding the amp by parallelling the amp input with the main speakers. You are using unshielded wire, and suspect either ground loop or the wire acting as an antenna.

Disconnecting the wires at the amp will not provide differential diagnosis between ground loops and the antenna question. You have to have two paths to make a ground loop. To diagnose between the two, I suggest disconnecting the wires at the receiver-end and bridging a resistor of around 10 ohms across the wires to simulate the existing load. If you still get the hum, the problem is probably the wires. To solve the wire problem, again assuming you are using the sub's amp, you should use shielded wire, with the shield grounded on one end, probably the sub-end.

If you have a ground loop, the first thing to try is putting a cheap isolation transformer on the TV cable lead-in, that is, assuming you have TV Cable. If that doesn't work, it's a more difficult problem to solve.

[auujay]

Thanks for the quick replys.

Ya I don't think that disconnecting the speaker wire per wid's suggestion will narrow it down much (though it would identify if the sub was being funky).

We have cable tv but it is not hooked up to this amp (but they probobly plug into the same outlet). You are right in the fact that the speaker cable is unshielded, unless opaque plastic counts ;) Yes the sub's amp is powering the sub. I am using the high level input instead of the line level inputs.

If I understand your suggestion Retread, stick a resister where the stereo (the Creek in this case) amp is and leave the sub on, plugged in, and attached to the speaker wire.

I won't be able to test this for awhile but when I do I will post with an update.

PS - For shielded speaker wire do you mean something like this (http://www.electronicsurplus.com/commerce/catalog/product.jsp?product_id=76201) which looks like basic 12 gauge twisted pair with a foil shield which is grounded.

[Retread]

Thanks for the quick replys.

"Ya I don't think that disconnecting the speaker wire per wid's suggestion will narrow it down much (though it would identify if the sub was being funky)."

I'm assuming that you initially powered the sub without wires connected and didn't have hum. If not, try that first. If it hums, you probably have a bad amp in the sub.

"We have cable tv but it is not hooked up to this amp (but they probobly plug into the same outlet)."

One of the problems with the typical home wiring system is that the electrical and cable TV are separately grounded, resulting in currents that should not be there circulating in the wires. Another problem that happens, not only in homes bu also in industrial and military settings, is reversals of the ground and neutral at outlets. This can result in massive circulating currents. When you have two devices plugged into such an electrical system, and then connect the two devices, this can result in differential voltages on the interconnecting wiring, which is very bad if the interconnections are carrying signals. These are sometimes difficult problems to solve. The U.S. military spent many millions of dollars some years ago just to correct reversals at the outlets of their communications sites.

"You are right in the fact that the speaker cable is unshielded, unless opaque plastic counts ;) Yes the sub's amp is powering the sub. I am using the high level input instead of the line level inputs."

Plastic doesn't count;-)

"If I understand your suggestion Retread, stick a resister where the stereo (the Creek in this case) amp is and leave the sub on, plugged in, and attached to the speaker wire."

You want to duplicate the wiring condition without the interconnection between the Creek and the sub. But you don't want to leave wires dangling open. If your wires go from the Creek to the speakers and then to the sub, disconnect them from the Creek and put about 10 ohms across each pair of wires at that point.

"I won't be able to test this for awhile but when I do I will post with an update."

"PS - For shielded speaker wire do you mean something like this (http://www.electronicsurplus.com/commerce/catalog/product.jsp?product_id=76201) which looks like basic 12 gauge twisted pair with a foil shield which is grounded.."

Yes, but Radio Shack carries a product called "audio cable" in 50' rolls that's a lot less expensive and will suffice. It's a pair of twisted 24GA insulated wires (one blue and one white) covered by a copper braid and a grey sheath. I don't know whether the black terminal of the sub's high-level input is grounded or floating, but I believe grounded. The shield braid needs to be grounded at one end, so I'd leave the shield ungrounded at the Creek-end and tie the shield and one of the wires (say the white) together at the sub and connect to the black terminal. Make sure to use the other color as the "hot" wire at both ends.

[wid]

Ya I don't think that disconnecting the speaker wire per wid's suggestion will narrow it down much (though it would identify if the sub was being funky).

That is what the intention of disconnecting the wires was about.

Disconnecting the wires at the amp will not provide differential diagnosis between ground loops and the antenna question.

If the wires are not connected to the sub at all then they very well can't act as a antenna causing the sub to hum.If you still have hum you would then know it's not the speaker wire.If all else fails just try a cheater plug.Hsu used to supply them with their subs for ground loop problems.

The problem is that there is a 60Hz hum (I assume it is 60, it is constant non the less) when the florencent light in the next room is turned on.

If by now you still have the problem.........get a new light fixture,non florencent,or try another outlet.