Post by pitviper33 on Nov 23, 2012 15:41:05 GMT -7
I JUST finished installing a new power amp for my mains and getting everything all dialed in again, and along comes a new, unrelated problem. Isn't that just the way it always happens?
As soon as I power up the subwoofer amplifier, the subwoofer starts making what sounds like a 60Hz hum accompanied by a steady "thump thump thump". Obviously describing a sound via text is pretty tough, so I made a quick recording of it. It seems my recording program (on my phone) must have a HPF or something, because when I play it back, the 60Hz hum is completely missing. Regardless, you can still clearly hear the "thumping". It's attached.
First I assumed a ground loop problem through the signal line. But nope. I unplugged the signal line, and the noise is still there. The recording you just heard was made with NOTHING plugged into the amplifier inputs. All that's hooked up in the back is the power cable and two sets of speaker wires, each to one driver. If it's plugged in and the power switch is on, the drivers are making that noise.
The amplifier is a Behringer EP2500. I know there's a lot of experience with this particular amplifier on this board. Has anybody heard this before? Any idea what could be wrong? The drivers are FiCar IB3 18s. There's about 15ft of 12ga wire between the amplifier and each driver, one to each channel of the amplifier.
Thanks in advance!
Last Edit: Nov 23, 2012 15:44:21 GMT -7 by pitviper33
Post by pitviper33 on Nov 23, 2012 17:50:40 GMT -7
The rest of the system is unaffected. No speakers other than the subwoofer are making strange noises.
Currently the amplifier itself isn't making any noise. It's the subwoofer making the noise when the amplifier is turned on. My expectation is that the amplifier itself will still make no noise with the drivers disconnected from it as you've suggested, but I'll try it to be sure.
It's the same amplifier I've been using since I built the subwoofer over six months ago. It gets used daily. I haven't touched the subwoofer wiring in at least a month.
Maybe the amplifier just decided today was its day to quit.
Post by pitviper33 on Nov 23, 2012 18:11:13 GMT -7
Alright I tried disconnecting each driver. The amp never makes any noise itself other than its normal cooling fan.
But in the process I did discover something unexpected. It seems the problem is only on output 1. If only the driver connected to output 2 is hooked up, the subwoofer doesn't make a peep (when not being fed a signal). If a driver is hooked up to output 1, the hum and thumping resumes.
So do I definitely have one dead channel here? That stinks. But I can probably run both drivers (4 Ohm) in series on one channel can't I? I know the amp won't put out as much power into 8 Ohms, but maybe it'd be enough for me. Thoughs?
And of course if anybody reads this and has seen a Behringer amplifier do something like this before, I'd love to hear if you found a way to fix it!
Post by pitviper33 on Nov 24, 2012 11:40:36 GMT -7
I spent a little more time playing with stuff.
Parallel mode: Thumping from the driver connected to output 1 (recording in post 1). Stereo mode: Same thumping from the driver connected to output 1. Bridged mono mode with drivers in series: Thumping seems to be twice as fast and possibly louder.
It seems like regardless of configuration, if amplifier 1 is hooked up to something, there's thumping. I guess it's fried.
Post by pitviper33 on Nov 29, 2012 21:49:02 GMT -7
I still don't know. Everything looked fine inside. No puffed up capacitors, charred resistors, or the like. I don't have a 'scope, so I could only look at the output with a multimeter. The multimeter was picking up on the 60Hz hum, but it wasn't telling me anything about the thumping. I left it powered up for a few minutes and checked temperatures all over the board. The only spot that got abnormally hot was near the front of the board at two adjacent potentiometers. I think it's unlikely that they were the root cause. My guess is that one of the solid state pieces had an internal short which then overloaded those pots.
Whatever the case, the amp is now up and running again! I found a post by someone over at diyAudio that had an EP2500 fail earlier this year. His had the power board fail. He agreed to send it to me for a very reasonable price. All I had to do was replace my bad amplifier board with the good one from the other amplifier, and it was good as new again. I definitely lucked out this time!
I'll hang onto the other amp just in case for the time being. If anybody else reading this needs parts from an EP2500 to get yours going again, let me know. I may have what you need!