Weird ground loop problem

[Dr. Bob]

I have had a strange problem I think is probably related to a ground loop issue. For some time, my setup has worked perfectly except that from time to time I got a wailing, screaming sound (like a monkey whose tail is being twisted) that would start suddenly, and stop just as suddenly. Since it was so intermittent, it was hard to track down. After reading about ground loops, I listened more closely and realized that there was a very slight 60 Hz hum. I tried the usual thing of plugging everything into the same power strip, and that didn't solve it. (Slight caveat: My power strip wasn't big enough to handle all the plugs, so I plugged one power strip into the first power strip.) I did track the issue down so far as to decide it was the subwoofer connection that causes the hum.

As the next step, I bought a ground loop isolater and put it into the sub connection. I tried it two ways: grounded to the chassis of my amp, and not grounded. This has made the problem worse! Grounded, it brought back the screaming monkeys. Ungrounded, it transferred the hum to the sub (while the main speaker hum went down), but it also brought on some loud pop/crackle noises. Even worse, after I removed the device, the 60 Hz hum was worse than before!

My setup: (Note there is no cable box.)
Marantz AVR (this has a two-prong plug)
Sony TV
Sony DVD player
Roku box
2 main speakers
2 surround speakers
subwoofer
PAC SN1 ground loop isolator

What else is there to try here? Can I, for instance, run a separate ground wire from the chassis of the AVR to the chassis of the sub? Any suggestions will be welcomed with thanks!

 

[TLS Guy]

I have had a strange problem I think is probably related to a ground loop issue. For some time, my setup has worked perfectly except that from time to time I got a wailing, screaming sound (like a monkey whose tail is being twisted) that would start suddenly, and stop just as suddenly. Since it was so intermittent, it was hard to track down. After reading about ground loops, I listened more closely and realized that there was a very slight 60 Hz hum. I tried the usual thing of plugging everything into the same power strip, and that didn't solve it. (Slight caveat: My power strip wasn't big enough to handle all the plugs, so I plugged one power strip into the first power strip.) I did track the issue down so far as to decide it was the subwoofer connection that causes the hum.

As the next step, I bought a ground loop isolater and put it into the sub connection. I tried it two ways: grounded to the chassis of my amp, and not grounded. This has made the problem worse! Grounded, it brought back the screaming monkeys. Ungrounded, it transferred the hum to the sub (while the main speaker hum went down), but it also brought on some loud pop/crackle noises. Even worse, after I removed the device, the 60 Hz hum was worse than before!

My setup: (Note there is no cable box.)
Marantz AVR (this has a two-prong plug)
Sony TV
Sony DVD player
Roku box
2 main speakers
2 surround speakers
subwoofer
PAC SN1 ground loop isolator

What else is there to try here? Can I, for instance, run a separate ground wire from the chassis of the AVR to the chassis of the sub? Any suggestions will be welcomed with thanks!

I don't think this is a ground loop. Am I correct in thinking that the only unit with a grounding plug is your sub? Or does no unit in the system have a grounding plug? Either way if there is only one ground, or no ground then you can not have a ground loop.

What drives your Sony TV? Is that connected to an antenna? If so is it inside or outside, and if outside, is there a grounding block? Is the TV connected to a cable or satellite system? Is there an Ethernet connection anywhere in the system, or is it Wi-Fi?

If there is only one ground or no ground, then I strongly suspect that your sub has a switching power supply that is failing and dangerously.

 

[PENG]

I agree with TLS that this is not a ground loop issue. Did the monkey scream only when a particular media source was played, or it could happen with any source (TV, DVD, music or video through the Roku box etc.)? If it could happen with any source then like TLS said, something may be failing in the sub. By the way, when did this problem start, from day one or just recently?

 

[Dr. Bob]

Hmm, it seems you're right - the sub is the only thing with a grounded plug. I had just assumed that the TV would have a grounded plug, too, but it doesn't.

I replaced the AVR and the sub around the same time. To the best of my recollection, the screaming only started after I got the new sub, but I'm not completely sure about this. It happens with all sources. Sub is a Rythmik E15, B stock.

TV is connected to a powered antenna. No cable box. Wifi only, no Ethernet.

OK, so, here's what I just did. I unhooked the Rythmik and hooked up my old BA sub, which has a two-prong plug. The hum in the mains went away!

So you think this is a problem in the sub? Anything to be done other than send it back? AN E15 is a pain in the butt to send back....

 

[KenM10759]

A number of commercially made subwoofers come with a 3-prong power cord...that has no wire on the ground contact. People will often replace the cord with one that's a different length, and problems start.

 

[TLS Guy]

Hmm, it seems you're right - the sub is the only thing with a grounded plug. I had just assumed that the TV would have a grounded plug, too, but it doesn't.

I replaced the AVR and the sub around the same time. To the best of my recollection, the screaming only started after I got the new sub, but I'm not completely sure about this. It happens with all sources. Sub is a Rythmik E15, B stock.

TV is connected to a powered antenna. No cable box. Wifi only, no Ethernet.

OK, so, here's what I just did. I unhooked the Rythmik and hooked up my old BA sub, which has a two-prong plug. The hum in the mains went away!

So you think this is a problem in the sub? Anything to be done other than send it back? AN E15 is a pain in the butt to send back....

Yes, I do think this is a problem with the sub. Call rhythmic and talk to them. You should only have to send back the amp and not the whole sub.

 

[Dr. Bob]

An update just in case others are following the thread:

I talked to Brian and Enrico at Rythmik, and they insisted it was a ground loop problem (tho I admit I didn't understand the explanation of how you can have a ground loop with only one ground in the system). They recommended using a cheater plug (3-prong to 2). That seems to have solved the problem: no more buzzing and (for the moment, anyway) no screaming monkeys!

Apparently they've been having this problem a lot because Enrico told me the newer subs will only have a 2-prong plug.

 

[TLS Guy]

An update just in case others are following the thread:

I talked to Brian and Enrico at Rythmik, and they insisted it was a ground loop problem (tho I admit I didn't understand the explanation of how you can have a ground loop with only one ground in the system). They recommended using a cheater plug (3-prong to 2). That seems to have solved the problem: no more buzzing and (for the moment, anyway) no screaming monkeys!

Apparently they've been having this problem a lot because Enrico told me the newer subs will only have a 2-prong plug.

If you are absolutely certain there is no other ground to your system then you did not create the ground loop. Brian and Enrico are talking out of the backs of their necks.

If this is a ground loop then Rhythmic created it. It has to be an internal ground loop in the sub. Worse, the screech would indicate that the ground plane is incorrectly thought out and instituted in that sub and causing periods of instability resulting in high frequency oscillation. I have never seen a ground loop between interconnected units result in oscillation.

Your next question to the happy duo at Rhythmic needs to be: - "Is that sub double insulated?" If it is then why did they ground it? If not their advice is dangerous.

If the sub is not double insulated, then you need to place one good ground at the receiver or pre/pro if that is what you are using. If you have one good ground then make sure the sub is unplugged before disconnecting the cable between receiver and sub.

 

[slipperybidness]

If you are absolutely certain there is no other ground to your system then you did not create the ground loop. Brian and Enrico are talking out of the backs of their necks.

If this is a ground loop then Rhythmic created it. It has to be an internal ground loop in the sub. Worse, the screech would indicate that the ground plane is incorrectly thought out and instituted in that sub and causing periods of instability resulting in high frequency oscillation. I have never seen a ground loop between interconnected units result in oscillation.

Your next question to the happy duo at Rhythmic needs to be: - "Is that sub double insulated?" If it is then why did they ground it? If not their advice is dangerous.

If the sub is not double insulated, then you need to place one good ground at the receiver or pre/pro if that is what you are using. If you have one good ground then make sure the sub is unplugged before disconnecting the cable between receiver and sub.

FWIW, Brian is an EE (and an acoustic engineer), if I remember, I think he is from USC. He designed these amps.

So, there is no doubt that he knows what he's doing here. Doesn't necessarily mean that this amp doesn't have a design flaw, or wasn't manufactured to original design specs.

But, I definitely have confidence in Brian, he is definitely someone that is passionate in his field, and he is educated in the field from a top level university.

For the OP: Is there a cable box or antenna with coax in your system? Those are notorious for introducing ground loops. And, which model sub are we discussing here?

 

[TLS Guy]

FWIW, Brian is an EE (and an acoustic engineer), if I remember, I think he is from USC. He designed these amps.

So, there is no doubt that he knows what he's doing here. Doesn't necessarily mean that this amp doesn't have a design flaw, or wasn't manufactured to original design specs.

But, I definitely have confidence in Brian, he is definitely someone that is passionate in his field, and he is educated in the field from a top level university.

For the OP: Is there a cable box or antenna with coax in your system? Those are notorious for introducing ground loops. And, which model sub are we discussing here?

There is something not right here. The generation of the high frequency screech inserting itself back though an output is very disturbing to say the least and absolutely not something that should be blown off.

 

[slipperybidness]

There is something not right here. The generation of the high frequency screech inserting itself back though an output is very disturbing to say the least and absolutely not something that should be blown off.

Yeah, I agree with you there, I would certainly be concerned with a noise "like a monkey getting its tail twisted".

 

[Speedskater]

Ground loop problems cause hum and low frequency buzz. High frequency screech is not a ground loop problem.