problem with subwoofers thumping out of control!

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BrettChaotix@gmail.com - 12 Aug 2006 17:49 GMT

I just replaced my 400w sub amp with a used 800w sub amp and I'm having
some wierd problems...

First, the setup is the rear-output of the headunit running to the
input of the amp (the amp does not have seperate rear/front inputs).

>From there I have the right-low output and left-low output running to

the subs. The amp is set on low-pass with the crossover all the way
over to the low end.

When I have the amp powered on the subs just produce a steady pounding.
It kind of sounds like the beat of house music at about 120-130BPM. It
does not matter if the headunit is even plugged into the amp - it still
thumps.

I'm hoping the wiring in the amp isn't screwed up - can anyone think of
anything that stands out as troubleshooting tips?

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MOSFET - 12 Aug 2006 18:42 GMT

It sounds like a phasing issue or some kind of feedback problem. Here are
some things to try, first and foremost, make sure your subs (you indicate
more than one) are wired in-phase. If your subs are wired out of phase, it
might DEFINITELY produce problems like you are describing.

Also, try summing the left and right channels BEFORE they go into the amp.
In other words, combine the left and right channels into one, then run that
into the amp. Actually, most amps when you run them in bridged mode are
designed to only accept one channel of input. But if yours does accept two
inputs even in bridged mode, try running them in mono.

Another thing to check is to make sure you have the amp bridged correctly.
Not all amps bridge the same way. Some have switches that must be engaged
while others do not (it's just how you wire it). DOUBLE CHECK YOUR WIRING.
Check the manufacturer's instructions for bridging.

MOSFET

>I just replaced my 400w sub amp with a used 800w sub amp and I'm having
> some wierd problems...
[quoted text clipped - 12 lines]
> I'm hoping the wiring in the amp isn't screwed up - can anyone think of
> anything that stands out as troubleshooting tips?

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Dark1 - 12 Aug 2006 23:31 GMT

it's a ground problem, there are a few possibilities, but the most common
would be a broken/loose ground pin on the amplifiers rca connector..
also possibly a burnt ground trace at either or both ends (amp or HU), or
with luck, a poor ground to chassis which is yet to cause that damage..
you'd be real lucky for that one..
anyway, not an expensive fix generally no matter which..

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Dark1 - 12 Aug 2006 23:41 GMT

> it's a ground problem, there are a few possibilities, but the most common
> would be a broken/loose ground pin on the amplifiers rca connector..
> also possibly a burnt ground trace at either or both ends (amp or HU), or
> with luck, a poor ground to chassis which is yet to cause that damage..
> you'd be real lucky for that one..
> anyway, not an expensive fix generally no matter which..

apologies, I guess I skimmed over the "doesn't matter if the HU is plugged
in to it or not" part.. well, first, don't plug it in as you could damage
your HU, and that narrows it down pretty well to either a bad chassis
ground, or a broken trace/connection in the amp...

>>I just replaced my 400w sub amp with a used 800w sub amp and I'm having
>> some wierd problems...
[quoted text clipped - 12 lines]
>> I'm hoping the wiring in the amp isn't screwed up - can anyone think of
>> anything that stands out as troubleshooting tips?

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MOSFET - 13 Aug 2006 02:51 GMT

I, too, failed to notice that the problem occurs whether the HU is plugged
in or not so obviously you can ignore my advice to sum the left and right
channels.

But I would double check to make sure that your subs are wired in phase (and
wired correctly to the amp) and checking the grounds wouldn't hurt. But I
agree it very well may be a problem with the amp such as a broken trace.

MOSFET

>> it's a ground problem, there are a few possibilities, but the most common
>> would be a broken/loose ground pin on the amplifiers rca connector..
[quoted text clipped - 24 lines]
>>> I'm hoping the wiring in the amp isn't screwed up - can anyone think of
>>> anything that stands out as troubleshooting tips?

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BrettChaotix@gmail.com - 13 Aug 2006 19:25 GMT

thanks for the tips guys, I've done a bit more testing and this is what
I've found:

I tried running the connection to the amp to each of the subs in the
box (the box has connectors for each subwoofer individually) - I did
it one at a time to make sure the problem happened with each speaker
being plugged in alone. It did.

If I plug both subs in together (a set of cables running to each
speaker) - it produces the same problem.

When I got the box I noticed the positive jack on one speaker, and the
negative jack on another speaker were "unscrewed" - making it look
like the last person to use the box had run one wire to each speaker
and they were bridged internally. I gave this a try and had no luck -
no sound was produced at all, not even the thumping.

I'll double check all my grounds but I don't think that's a problem
(unless it's a problem inside the amp itself) because when I hook my
old amp back up and then plug in the new 2-speaker box, I have no
problems and it sounds ok playing music.

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