Specific troubleshooting tips:
- Cause (1), a bad subwoofer power supply, can be checked by simply unplugging the input cable from the sub and seeing if hums with no input.
- Cause (2), induced hum in the subwoofer cable, is normally caused by the cable being too close to power cords -- check cable spacing. If this is the cause, the problem will likely vary in intensity as you increase or decrease the spacing between signal and power cables. The strength of this interference is inverse to the square of the distance, so small amounts of adjustment can make large differences!
- Cause (3), hum getting into the signal path prior to the sub cable, is harder to diagnose, but usually the way to proceed is to test what happens when you switch or disconnect individual sources from your amp. Unplug them from power, too, if possible, as this will prevent upstream ground loops from being a factor. If the problem is specific to a source, then most likely either the source is generating the hum or there is a ground loop issue between that source and your amp.
If the more common ground-loop issue between receiver and sub, (4) above, is your only problem, this transformer will resolve it. This isolation transformer is a quality, US-made audio transformer which eliminates the need for a straight-through ground/ground connection between your receiver and your powered subwoofer. With the grounds on both sides isolated from one another, ground current wont flow down the shield; the result is elimination of ground loop hum. We recommend it be used with Blue Jeans Cable LC-1 subwoofer cables, which are heavily shielded to reduce induced noise, for a truly quiet, low-noise-floor subwoofer.