Active monitor problem
 

Hi all,

I have a pair of M-Audio SP-5B active monitors. I know they're not great, but for my needs (basic mixing of narration with music beds) they serve me well and have done for a good number of years.

This morning, though, one of the monitors has developed a fault. I've attached a wav (volume greatly exaggerated) which contains the sound when the speaker is first switched on. Sometimes the surge sound at the end is longer and louder, other times it's quite quiet. The background buzzing continues as long as the monitor is on (even with the volume turned right down). Additionally, any audio played through the monitor sounds like it's clipping, i.e. distorted.

My first thought was that the cone had cracked but close inspection reveals nothing obvious. The fact that the buzzing occurs even with no signal being sent to the monitor makes me wonder if this sounds like a failing transformer issue.

Steps taken so far:

Checked audio signal levels - OK
Swapped power and XLR with other speaker - OK
Inspected speaker cone internally and externally - OK (as far as I can tell)
Moved monitor away from any potential interference (although it has been in the same spot for at least five years!)

Any advice will be welcomed.

Thanks,

Ian . . .

If you've switched audio and power cables and the problem didn't follow, but stayed with the "bad" monitor, I think you've isolated it.
Did you thoroughly work the volume control many repetitions and listen if that is crunchy or changed the problem in any way? (I know you said it still hums with the volume all the way down.)
If you have access to repair it cheaply, that's an option, but really I think I'd re-task or sell the good monitor, give away the bad one for parts, and buy a new set of equal or even better monitors.

Possibly a bad filter capacitor, if you're handy at stuff like that, look at the circuit board and see if there's a swollen or discolored capacitor...they can die with no outward signs, of course. The often-cheap caps on these boards are a frequent source of trouble...