I recently bought a used MTX Thunder 500D amplifier off ebay. I hooked it up to an Ascendant Audio Atlas 12" sub which is rated for 300 watts rms at 4 ohms.

When I begin to turn up the gain on the amp, I start getting an odd humming sound that seems to cause the sub to go into a feedback loop. The sub seems to oscillate at a very low frequency when this happens.

The only way that I can play the sub is by turning the gain almost all the way down. When I play it with these settings the sub sounds clean, but it doesn't get very loud.

The loud humming also happens when I have the music paused. I know it's not a bad ground because I had an cheap Alphasonik amp connected to these same wires, and it didn't make any noise at all, even with full gain.

Could this be a faulty amp which needs repair?

Tomorrow I'm going to add another Atlas 12" to the system, and I'll see if it plays much louder. The strange thing is that it doesn't sound like distortion at all. Just a loud humming sound.

 

Could it be your ground?

 

The ground is good.

The following is a response I received from MTX:

"It could be a bad amp, you will want to remove it and have it bench tested, we can no longer repair that amp due to lack of parts. We can offer you an upgrade to an 801DR, with the trade in of your amp it will only be 160.00 dollars. Please call 1-800-call mtx, if you are interested, Thanks"

The funny thing is that after hooking up the second sub, it sounds alot better. It took quite a bit of tinkering with the crossover and the gain, but it finally sounds good. I think the reason it doesn't get extremely loud is because these are SQ subs and don't have the greatest output.

 

That's a great deal, do the trade!
I'd also say something may be wrong with the amp despite your results.
Looks like MTX wants you as a customer, I'd go for it.

 

I agree that something might still be wrong with the amp, but alot of people are saying to stay away from the newer MTX amps.

The 500D is a great amp, so I think it's worth trying to get it fixed. There was a review done on this amp which shows that it can put out a kilowatt at 2 ohms. Not bad for something I picked up off ebay for $150 CDN.

The ebay seller even had a 7-day DOA policy, but unfortunately I didn't hook it up until 15 days later.

I'm going to see if I can get it bench tested.

 

I am not sure who told you to stay away from NEW MTX amps. I would venture to say they know little about Car Audio and have formed there opinion from some other buddy that heard a rumour. They are the best quality amps hands down in years!!

The 801DR is a refurbished 801D and not current in MTX line up anymore.

If you were happy with the 500D then get the 801. The 500d was most peoples least favourite MTX amp in 10Yrs.

 

Then why is it that when you look at the review forums, the MTX Thunder 500D receives excellent reviews.

Thunder 500D reviews

4.64 out of 5 with 33 reviews


The only time the amp has any odd behaviour is when I turn the gain higher than halfway. The way I have things set right now, it actually sounds very good. Since I'm into SQ and not SPL there's really no need for anything more. There's a chnace I might not even get the amp fixed because it sounds fine now. I realize that a defective amp can cook my subs, but since it only misbehaves at high gain levels, then It should be okay the way things are now.

 

I am not saying that the 500d was a bad amp, but when comparing its quality/design/performance ect.. to other amps of previous or newer models, its easily most MTX enthusiast least favourite.


This comment you made

"I agree that something might still be wrong with the amp, but alot of people are saying to stay away from the newer MTX amps."


The only reason someone would say that is because they have zero experience with new MTX amps.

Or its a simple case of what I call "My Buddy told me this"

One day I would love to meet this buddy everyone talks about.

[ October 15, 2005, 10:06 AM: Message edited by: MITEK CANADA ]

 

2nd review I read in that link:

this amp was THE worst ever. It blew on the first hit, i got a new one and it caught on fire!! WHAT A PIECE!!! I suggest u buy a pyramid before mtx. [img]graemlins/laugh.gif[/img] [img]graemlins/bow.gif[/img]


Dude- I doubt its the amp... taking it out for a bench test would be a waste of your time in my opinion.....

Chances are you have some ground loop going on.... crank the gains with some muting plugs hooked up and see what happens.... my bet is you will be noise free....

 

FWIW, I absolutely loved my 6500D, I bought it used on here (from seahag I think it was), It was one of the most reliable amps I've ever owned, a little bit of a current hog (for a D class) but that was my only complaint. I just sold it not too long ago because I wanted to take another step up in power.

Check for ground loops. It doesnt sound like the amp is the problem.