subwoofer hum solved,but I had to unground them

My subs had a real loud hum and I had to unground them to stop it.They are sounding good still.The rest of my equipment is two blade(no ground).Is it ok to leave my subs ungrounded or does it present a danger.BTW I have a 6 outlet adapter that I broke the ground tab off of and that is what Im using on the subs.

 

You were creating a ground loop. The third wire which you removed must have been attatched internally in the subwoofer to the chasis ground of the subwoofer. What has happened is that you also have a ground on the rca jacks plugging the subwoofer into your preamp, or from where it is sourced.

You should really have only one main ground point. If your case you were attaching the power cord ground to the chassis ground and they have a slight difference in voltage on them. An ideal ground will have no voltage, but in the real world that is not the case. The voltage is usually pretty low. That difference is being amplified as hum.

I've run into these issues in studio's and there are basically 2 ways to solve this. One is to go inside the equipment and remove the power and or chassis ground from the amplifier common. This is not always so easy. The other method is to simply remove the ground connection from the power cord. This is normally fine to do.

One must consider the purpose of this ground wire though. It is there as a protection. If there is ever a short in the amplifier it is nice to have a ground for the current to dissipate through. If not, current may go another route which could damage other pieces of equipment which are connected to that ground or even a person if he offers a good path to ground. Electrons always follow the path of least resistance to ground. It is pretty unlikely for this type of failure to occur but it is possible. Often I insert 3-2 Edison adapters on the ends of the power cords which is basically what you have done. This is a quick fix and often it becomes a permanent fix.

This doesn't apply to you, but in the studio, removing the amplifier common from the chassis and power cord is often the best approach. Even if you take the power cord out of the picture, if equipment is screwed into a common rack, there is another source for ground loops. Disconnecting the common grounds from the chassis can eliminate this problem. Sometimes this can be done by simply removing a jumper. Other times it requires internal modification.

 

Is it normal for this hum to start out real low and increase to it max loudness after a few seconds after turning the subs on? also they send the humming into me reciever even when they are turned off! it sounds like static out of the tweeters.This all happened while they were grounded.Will my subs max output change with out a ground?

 

This leaves nothing grounded at all.I have an onkyo reciever.should I buy a 3 prong adapter plug that has a solder tab and run a ground wire to it and ground only the reciever?

 

I don't understand the hum increasing in volume, but turning the subs on and off will have no effect since the ground loop is there even with the power turned off. The ground should have no effect on the gain of the sub.

Possibly the hum increasing could be the result of a turn on delay relay, but that doesn't make a lot of sense, unless it removed the ground. And then if so, you'd not have the hum with the sub turned off. Perhaps the hum is just increasing in the sub and not in the mains. If so, the turn on relay or delayed ramp up in volume could be what is happening.

 

It is helpful to have the main system grounded at 1 point, but I've seen systems work just fine without this. What will happen in this case is the ground will be floating. It would be a good idea to ground the receiver to a good ground. Ideally this is a stake in the ground, or a water pipe, but in a pinch the ground screw of the power outlet might work. I tie my main ground to the ground point between the filter caps on the power amp. But I wouldn't futz around inside your receiver unless you are sure you know what you're doing.

Turn up the gain real loud, but don't play anything. Listen to the hum by putting your ear to the speaker to evaluate different grounding points. I've even seen systems where the noise gets worse when you tie to a ground, but that is usually an indication that something else is messed up. But whatever works. If you don't hear much hum, I wouldn't worry too much about lack of a good ground.

 

when the buzz happens in the mains it is there with the subs on or off and it does not increase or decrease in volume.only in the subs does the hum start low and increase after about 10 seconds when grounded.

 

Then it's probably a time delay circuit in the sub amp and perfectly normal.

 

this is after the amp clicks its relay In

 

Yes, That is what I would assume. Many amps have time delay circuits which turn them on after a short time. This is done for many reasons. Usually it is to prevent other parts of the system from popping when the system is turned on. Suppose when you first turn on your system, something thumps. By the time the sub relay kicks in, the thumps should be done thumping.