panteragstk

panteragstk

Audioholic Spartan
Well, I got a new amp for the theater subs (Crown XLi 800) and while it works great...it has a hum. Very slight, but I noticed it so now I can't un-notice it.

The XLS1500 powering the rear subs is dead silent. Both amps are fed from a y cable coming off each sub channel on the back of my 4300h.

I have a monster power center (surge protector) that is "supposed" to isolate different sections from each other, but it does nothing. As expected.

Hum is very soft, but in the dead silent room it is slightly audible, which is too much.

I'm thinking it's just the cheap amp. It even says in the instructions to keep it away from the processor due to transferring hum.

"it has a strong magnetic field which can introduce hum into unshielded devices that are located nearby." Interesting because nothing but the two subs hooked to it are humming.

Dammit. :mad:
 
lovinthehd

lovinthehd

Seriously, I have no life.
Believe your XLS manual has the same warning, tho. Is it a ground loop hum you can check with lifting the ground? or physical transformer hum or ?
 
S

Speedskater

Audioholic Chief
Try removing the monster power center. Then using extension cords, power everything from the same AC wall outlet.
 
panteragstk

panteragstk

Audioholic Spartan
Believe your XLS manual has the same warning, tho. Is it a ground loop hum you can check with lifting the ground? or physical transformer hum or ?
From what I remember from my days selling pro amps and speakers, it just sounds like transformer hum. It isn't a ground loop from what I can tell. Amp just doesn't have a good noise floor. I seem to remember it being quite common from the class A/B amps on the lower end.
 
panteragstk

panteragstk

Audioholic Spartan
Try removing the monster power center. Then using extension cords, power everything from the same AC wall outlet.
I have two individual 20a outlets for my theater. The amps are on one, the receiver, server, and shield TV are on another hooked to a UPS.

I also have another outlet that is separate from the theater outlets in that it is just in the same group as the rest of my room where the rack sits. Same issue when plugged in all by itself. Pretty sure it's transformer hum and isn't going to go away.
 
lovinthehd

lovinthehd

Seriously, I have no life.
Open it up and see if you can tighten down the transformer? I had to do that on one of my old Carver amps recently....
 
panteragstk

panteragstk

Audioholic Spartan
Open it up and see if you can tighten down the transformer? I had to do that on one of my old Carver amps recently....
Good point. It did just get shipped from Amazon so it may have not been treated all that well.
 
lovinthehd

lovinthehd

Seriously, I have no life.
Honestly, having been around so many pro amps over the years, some of them just sound like this. In a live venue it would never be noticed.
Yeah I don't know if that's typical of that model line, I know my various XLS amps haven't had such an issue (let alone fan noise).
 
panteragstk

panteragstk

Audioholic Spartan
Yeah I don't know if that's typical of that model line, I know my various XLS amps haven't had such an issue (let alone fan noise).
Mine either. The class D pro amps I've used have an excellent noise floor. I just didn't recognize the sound until you said "transformer hum" then it clicked. I've heard it before, but it's been 11 or so years. This is a low man on the totem pole anyway, so I can't complain.

You'd probably notice it too if you were in my theater, but I can bet nobody else will notice. Maybe my brother, but that's about it, and that's only because he installed AV and is a musician used to pro gear.
 
TLS Guy

TLS Guy

Audioholic Slumlord
From what I remember from my days selling pro amps and speakers, it just sounds like transformer hum. It isn't a ground loop from what I can tell. Amp just doesn't have a good noise floor. I seem to remember it being quite common from the class A/B amps on the lower end.
We need to know more about it. By transformer hum, you mean the hum is actually coming from the map and not the speaker. Can you hear the hum, with no speaker connected? If he hum is from the speaker, do you hear it if you disconnect the input? If the hum goes away when you disconnect the input, the is the amp is grounded, then lift the ground and see if the hum goes away. Please report back the answers to these questions and we can give you an answer.

You may have mechanical hum

You may have a ground loop.

You may have RF noise.

You could have a faulty amp.

We can sort this out with applied logic, if you answer the above questions.
 
panteragstk

panteragstk

Audioholic Spartan
We need to know more about it. By transformer hum, you mean the hum is actually coming from the map and not the speaker. Can you hear the hum, with no speaker connected? If he hum is from the speaker, do you hear it if you disconnect the input? If the hum goes away when you disconnect the input, the is the amp is grounded, then lift the ground and see if the hum goes away. Please report back the answers to these questions and we can give you an answer.

You may have mechanical hum

You may have a ground loop.

You may have RF noise.

You could have a faulty amp.

We can sort this out with applied logic, if you answer the above questions.
Well, I stand corrected. It's not what I thought at all. If the input is removed, dead silence. This got me wondering so I went to the subs that are hooked to the XLS1500 and sure enough, they have a very slight hum. You really have to put your ear to the sub to hear it, but it's there.

So, the input is the issue. I wonder if the Y calbes I bought could be the culprit? I'll have to see if I have any other Y cables.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Well, I stand corrected. It's not what I thought at all. If the input is removed, dead silence. This got me wondering so I went to the subs that are hooked to the XLS1500 and sure enough, they have a very slight hum. You really have to put your ear to the sub to hear it, but it's there.

So, the input is the issue. I wonder if the Y calbes I bought could be the culprit? I'll have to see if I have any other Y cables.
Well you have narrowed this down to a ground loop or RF.

Does it stop if you turn off all LED lights in your home and switch any SCR dimmers to off?

Which units are grounded and which not? What is your TV and Internet service and how is it connected?
 
panteragstk

panteragstk

Audioholic Spartan
Well you have narrowed this down to a ground loop or RF.

Does it stop if you turn off all LED lights in your home and switch any SCR dimmers to off?

Which units are grounded and which not? What is your TV and Internet service and how is it connected?
Does it matter that it is plugged into a dedicated circuit?

Internet is fiber, no TV service that isn't streaming.

I'll have to check on the LED lights being turned off. I have quite a few z-wave dimmers as well. Never been an issue before (that I noticed anyway). This amp seems to have exposed this issue in a more obvious way.

I do have a seperate ground option on my monster power strip. Not sure what I'd ground it to being on the second floor. Not sure if that would help either.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Does it matter that it is plugged into a dedicated circuit?

Internet is fiber, no TV service that isn't streaming.

I'll have to check on the LED lights being turned off. I have quite a few z-wave dimmers as well. Never been an issue before (that I noticed anyway). This amp seems to have exposed this issue in a more obvious way.

I do have a seperate ground option on my monster power strip. Not sure what I'd ground it to being on the second floor. Not sure if that would help either.
Fiber Internet cable is still grounded by code and can still be a source of ground loops.

The dedicated circuit is not an issue.

So disconnect your internet connection first and see if that stops the hum. Then lift each ground in turn of three pin connected devices, with a cheater plug to see which ground may be the source of the ground loop.
 
S

stalag2005

Audioholic
If you have two pieces of equipment with a ground screw, get a wire and bond the equipment together. Chances are if the hum is not due to the electrical ground it could be due to a difference of potential between the equipment. If this stops the hum, you are golden. If there are more pieces of equipment with this terminal bond them also. That grounding terminal is to balance potentials and is not a safety ground.
 
panteragstk

panteragstk

Audioholic Spartan
So, I did some testing and some things I'm not able to test yet. Internet being one. Can't turn it off as my network would freak out a bit. Plus, have to have it to work.

Anyway, I'm not sold on it being a ground loop. Here's why:

If I unplug the cable from the receiver, no hum. If I plug the cable into the receiver, hum. If the receiver ISN'T plugged into the wall, hum.

One would think that if the receiver isn't plugged in, and the issue is a ground loop, then there would be no hum. There still is. As long as the cable is plugged into the receiver, I get a hum. Receiver being on or off has no effect.
 
S

stalag2005

Audioholic
Grounding is as much an art as a science. We had a problem with a studio feeding back into the electrical lines for similar issues. One is not to hear the group Petra (I have the CD) in the managers office when I am playing it in a studio across the facility (rooms not next to each other). The solution was to bond all the equipment together and that eliminated the feedback. O, by the way, my partner was playing that CD in his studio without any interconnect........Audio can be strange! Those posts for ground is to bond the equipment together to relieve potentials between the circuits. In the case of audio ground it is not safety but to equalize potentials.

Doing this can also eliminate the hum
 
S

stalag2005

Audioholic
If it is a network cable the cat7 standard is shielded end to end and may help with bonding your network devices. Cat7 is the standard rj45 connector and will work with your current equipment. I use cat 7 myself.
 

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