[cacu]

I'd finally completed my DIY Tempest sub project. I'm using the Rythmikaudio 350w amp. I find that when the amp is plugged into the power outlet it makes a humming noise. Not very loud but audible at close range (less than 1 foot away). Is this typical or is there a problem?
Note: I've tried unplugging the speaker and the line-in and still same result. The amp makes the noise on its own even in the off mode.

Here's a link to my DIY page.
http://www.crazyvu.com/diy_sub/diy_sub.htm

[TimForman]

Have you tried it in a different outlet?

[cacu]

Tim Wrote:
Hey cacu,
You may want to get a SPL meter. The bass from the MidQ can be deceiving if you're used to boomy bass. It might be louder than you think. Plus, it could be that because of the shape of your room you have some nulls taking out the frequencies you're looking for. Are there other spots in the room you could try placing the sub?
=======================================
Hey Tim,
I went to our local RatShack and got an SPL meter for $25. Went home and calibrated my system with Sound&Vision Home Theater Tune-Up DVD. Sure enough my Amp level is set way too high compare to the front mains. It was way over +10db compared to my fronts. So I calibrated it. Made it around +3db above the fronts.

Then I play my usual music and sure enough it was great. So I cranked it up and watched the SPL meter. It started clipping at around 112db. It easily handled 100db range perfectly.

So the moral of the story is: You are right. It is louder than I thought. Now let see if I can get rid of this amp humming problem.

[Jeffrey Noel]

cacu,

You might try using a cheater plug (an adapter that changes the three-pronged plug to a two-pronged plug). I don't know if it's the same problem that I had with a humming Behringer Feedback Destroyer, but it sure fixed the problem. It was only a 49cent fix!

But, the humming amp problem could be the exact problem the DLS 10" Sub from Parts Express was having. They have since discontinued the sub for this reason. I have one of the amps that hum and I could hear it across the room. PE sent me a new amp and it works perfectly!

I'd highly suggest contacting Rhythmic Audio about the problem.

[TimForman]

Quote:

You might try using a cheater plug (an adapter that changes the three-pronged plug to a two-pronged plug).

That was my first thought too but then he said that it hummed with the speaker off so that seemed to point to the amp circuitry. Just to cover that base for sure I suggested a different plug. Sometimes certain household outlets are not grounded properly while others are. I'm inclined to agree about a defective amp though. You might try different outlets anyway. Doesn't cost anything.

[Peter Jessee]

The hum could be 60 Hz leaking through the power supply or from a grounding problem. It could also just be the layers of the transformer core vibrating and actually creating an audible noise. If you only hear it from the amp (NOT the driver) and it's pretty faint, that's probably what it is. If it doesn't get any louder, it shouldn't hurt anything.

Peter

[cacu]

At the suggestion of Brian Ding at Rythmikaudio I tighten the screws behind the power plug and also bought the cheater plug. It seems to help. I can only hear the hum when I put my ears about an inch from the cabinet. But to be honest the hum wasn't very loud to begin with. The problem is that this is my first DIY project with the plate amp so I didn't know what to expect but Brian Ding was very helpful, he offered to exchange the amp. I didn't think it was necessary since there's really nothing wrong with it.

Overall I'm happy with the amp and the sub. I'm beginning to think of the next DIY sub already. Maybe a ported Maelstrom next time since I need the punch for my big room.