Monday, February 16, 2009

Have you heard the buzz?

If there is hum or buzz in your audio system diagnosing the cause is often a frustrating task. Begin by asking yourself some questions. Is the hum at 60Hz? If you have a test CD that has a 60Hz tone use that as a reference for comparison. If yes you are certainly dealing with an electrical issue.

If it's only on your phono input. How close is it to other equipment? One thing to always keep in mind is that the signals that phono preamps are dealing with are absolutely tiny. Much smaller than the line out of a CD player for example, about a tenth the size. The wiring in a tone arm and the interconnects that come from the turntable are likewise vulnerable. I ran out of rack space and instead of stacking my phono pre on top of or behind something I placed it on an adjacent book shelf which did two things. First, it made sure that the unit wasn’t close to the power supplies of other components. Second, it kept the interconnects from the ’table to the phono stage away from all of the other cables in the system. You might also try turning off Digital components when listening to the analog front end because they put out a lot of RFI and EMI.

Hum is normally caused by different grounding potentials. Many times it’s because a video monitor that is connected to cable TV is also connected to an audio system. Is your system connected to a video source? The Cable and satellite Companies are required to ground THEIR system and of course the electrical system has it’s own ground already. This, of course leads to the possibility of two different grounding potentials. Electricity, like water flows to the path of least resistance and that is what causes the hum. Another thing to think of with old wiring is that you might have grounded outlets that aren’t properly grounded because the original wiring job is two wires (hot and neutral) and the conversion wasn’t done properly. This can be tested by a $5 tester that can be purchased at any hardware store. It plugs into the outlet and through a series of lights can diagnose bad grounds, hot/neutral swaps, and a number of other conditions. It’s a small price to pay for piece of mind

Are the audio outputs of TV, Cable box, or the DVD player hooked up to the audio system? If so the audio cable's ground is introducing the second ground. As a diagnostic step try disconnecting the coaxial cable that carries the TV signal that goes from the wall into the cable box. If the hum goes away then we know that the hum was caused by having two grounds with different potential.

If the ground is the problem try:

Xantech 634-00-This one is only about $9 but it tends to knock out higher TV stations in digital cable systems and negatively affect pay-per-view and movie on demand capabilities. It's cheap enough to try and throw away if it doesn't work. But in my experience it usually causes some kind of problem. I only mention it to present all options.

Mondial Magic Box-It's about $100. Which is expensive by comparison but because of it's greater bandwidth tends not to knock out higher TV stations in digital cable systems. Nor does it usually cause problems with pay-per-view and on demand functions.

Tributaries used to make one but it doesn't look like it's available any more. It worked as well as the Mondial.

1 comment:

Clint said...

Or as Chubby Checker sang: "Do you remember when... things were really hummin'?"