HELP - Descent hummmmmmmmm

[Pcar928fan]

My Descent hummed whenever it was plugged in, whether there was a signal going to it or not. I tried a simple little 99 cent "ground plug adapter" from the hardware store. It cured the problem completely and has been working for the last three years. Try it, it may work for you.

What kind of ground plug adapter is that? Are you talking about one of those plugs that takes you from 3 prongs down to 2? I have some of those around. Can't hurt to try it I guess. My problem though is when ANYTHING is plugged into the LFE input on the back and it is turned on...just a low level hum that if everythig else is quiet you hear.

When I finally have a home theater that will be annoying right now it is really no big deal...

 

[IWalker]

I would pick up one of those 3-2 plugs just for testing purposes. Throw it on the Descent cord and see if it makes a difference. If so, you've just identified that it's definitely a ground loop problem.


I had a similar issue with my mains. Everytime I plugged in my laptop, and then connected the sound card to the DAC I got a bad hum. Unplugging the laptop fixed the issue. Plugging it back in brought back the hum. What I would do is trace the issue back component by component. It's harder if you have a receiver, but should still work. Basically, unplug the LFE input from the sub. Does the hum go away? Yes? Good. Now go to the receiver. Unplug each component 1 by 1. If removing any one of these removed the buzz from the sub, you've found your issue component...if you get everything unplugged and it's still buzzing, unplug your speakers from the receiver. Now it should be just the wall power and the sub attached to the sub. If you still have the buzz, use the 3-2 plug on the receiver (though often they only have 2 prongs on their plug anyway. If you still have an issue...plug the receiver directly into the wall, and unplug your surge protector.
(if you have a pre/pro...the same steps apply...just disconnect the amp when you would disconnect the speakers in the above steps)

If none of these identify the issue, you likely have a busted receiver/pre...though it COULD be some issue with the descent. If the descent hums without any LFE input...it's most likely the descent.

I would guess that either a computer or cable box is causing the issue. If not that, probably the pre...either broken or with a setting it doesn't like.

 

[timm]

IWalker--

There is no hum on mine without the lfe plugged in. However, it is so loud - and there is no bass response. It is fair to say - I would assume - that a ground loop would not impact bass response - loudness of bass etc...Mine sounds like an internal short. I also have no other hum in any other components. I am assuming you had bass w/hum. The last time I listened to mine prior to fed-ex picking it back up - I had my ear down by the woofer and the only reason I knew there was any signal at all was by putting my hand on the woofer and feeling a very slight vibration from a drum beat.

 

[IWalker]

The hum sounds like a ground loop, but the lack of bass response is either an issue with the pre/receiver or with the descent input. I had hum in a sub where there was no hum in the rest of the system. I also had EQ hooked up to it, and if I put a notch filter on it at 60HZ, it almost entirely eliminated the hum...which told me it was definitely ground loop. If you are sending no signal, and still have a hum/vibration...then it's almost definitely that. No idea on the no signal part, unless it's a setting issue or something that requires a repair, either in the sub or pre/receiver. I hope it is a defect, so that will solve your issue...but if it is confirmed working...start looking at your pre....either settings or maybe a defect in it. It's a shot in the dark though without being able to see it myself. Sorry, wish I could be more helpful!

 

[timm]

No - everyone here has been VERY helpful I have two subwoofers - the descent and a paradigm which will be replaced by it. If I connect to the paradigm - no hum. When I disconnect the paradigm and put the descent in its place.... then the problem occurs. The one diff between the paradigm and the descent is the 3 prong plug. The paradigm has a 2 prong plug. I guess my question was - even with a ground loop - annoying as a hum might be - a solid bass signal should be had. (I'm trying to justify my conclusion that there is something wrong with the sub). Once fed-ex gets it back to me - I can verify it by bringing it to my dealer - out of the house - and have him hook it up.

Anyway - to all - once this is figured out.... I will put something out comparing a sub like the descent to a 350 dollar sub like the paradigm pdr-10 (a 'good value' sub) and the differences and improvements vs cost. Hopefully some will find it interesting.

 

[Craig]

I'm willing to bet there is nothing at all wrong with your sub.

A short in your sub is certainly a possibility but a ground loop interference is more likely what is happening here. The steps you've taken so far have not done anything to rule out Ground Loop Interference (GLI).

However, it is so loud - and there is no bass response. It is fair to say - I would assume - that a ground loop would not impact bass response

No, I don't think that is a good assumption. If a GLI is dominating your LFE input then it why wouldn't a GLI problem effect bass response? Of course it would. Especially if it is a loud humm.

The one diff between the paradigm and the descent is the 3 prong plug. The paradigm has a 2 prong plug.

This test would lead me to suspect a GLI problem when using the 3 pronged sub. The reason your Paradigm has no GLI problem is solely because it has no ground connection. A 3-2 (cheater plug) plug eliminates the ground circuit from your sub which will identify a ground loop issue if there actually is one but we still don't know since you haven't tried that yet. Connecting your 2 pronged Paradigm sub is not going to identify a ground loop interference even though a music signal is successfully passing through your LFE output.

The Paradigm is designed with no ground wire to avoid GLI issues. With no ground wire there can be no GLI issues even when a grounded sub indicates a GLI problem. If there is a GLI issue with a sub, the sub is not to blame. The signal to the sub is at fault and is often caused by the cable company using a different ground system than the house wiring circuit. Elminating either the house ground or the cable ground will usually eliminate the humm. Also try completely disconnecting the cable from the system.

Unfortunately the higher-end circuitry in the Descent requires a ground so it can function when using the balanced input. I'm hoping the new Descent i and Depth i have solved GLI conflicts with thier new circuits.

Until you spend $2 and 2 minutes to try the cheater plug test and/or disconnect the cable from the system you won't know if it is simply a bad case of GLI or not.

(I'm trying to justify my conclusion that there is something wrong with the sub).

I have to agree with you on your statement.

 

[Tj Bassi]

I run both of my Descents with the cheater plug. After a whole week of trying to find the ground loop, I noticed one quiet evening (while the system was off) that the Descent, which had a slight hum even while in standby, became a bit louder when the fridge was running. The cheater plug did solve that...kinda hokey in practice but it did the trick.
I also used an Audioquest sub-X cable with the little ground pigtail, which did not seem to make an improvement. Disappointing....it was an expensive cable

Tj

 

[timm]

I'm willing to bet there is nothing at all wrong with your sub.

A short in your sub is certainly a possibility but a ground loop interference is more likely what is happening here. The steps you've taken so far have not done anything to rule out Ground Loop Interference (GLI).



No, I don't think that is a good assumption. If a GLI is dominating your LFE input then it why wouldn't a GLI problem effect bass response? Of course it would. Especially if it is a loud humm.

This test would lead me to suspect a GLI problem when using the 3 pronged sub. The reason your Paradigm has no GLI problem is solely because it has no ground connection. A 3-2 (cheater plug) plug eliminates the ground circuit from your sub which will identify a ground loop issue if there actually is one but we still don't know since you haven't tried that yet. Connecting your 2 pronged Paradigm sub is not going to identify a ground loop interference even though a music signal is successfully passing through your LFE output.

The Paradigm is designed with no ground wire to avoid GLI issues. With no ground wire there can be no GLI issues even when a grounded sub indicates a GLI problem. If there is a GLI issue with a sub, the sub is not to blame. The signal to the sub is at fault and is often caused by the cable company using a different ground system than the house wiring circuit. Elminating either the house ground or the cable ground will usually eliminate the humm. Also try completely disconnecting the cable from the system.

Unfortunately the higher-end circuitry in the Descent requires a ground so it can function when using the balanced input. I'm hoping the new Descent i and Depth i have solved GLI conflicts with thier new circuits.

Until you spend $2 and 2 minutes to try the cheater plug test and/or disconnect the cable from the system you won't know if it is simply a bad case of GLI or not.

I have to agree with you on your statement.

Haha... very good. Thank you for picking that apart...when I said 'assume' - I meant exactly that.... My predicament was simple - it was delivered on 11/29 and opened 12/24...it was insured...fedex wanted it back. I just wanted to bring it to my dealer. Problem: my back is KILLING me. FedEx all ready had it when someone suggested the cheater plug...Trust me - I would have tried it if the sub was in my possesion. I included the info on the paradigm hoping someone would jump on that as a reason why the paradigm was fine. I thought it to be a possibility - but really have no experience with ground issues. I don't think any of my equip (sunfire amp/pre - denon 5900) uses a 3 pronger. Only the descent.

Sounds like if cheater plug is used - no balanced connection can be used....based on your statement.

Once I get it back - I face the decision of trying the cheater (hauling it down my basement steps...unpacking...etc...or just driving to the dealer and having them try it there. (read above: my back is KILLING me... )

 

[timm]

I run both of my Descents with the cheater plug. After a whole week of trying to find the ground loop, I noticed one quiet evening (while the system was off) that the Descent, which had a slight hum even while in standby, became a bit louder when the fridge was running. The cheater plug did solve that...kinda hokey in practice but it did the trick.
I also used an Audioquest sub-X cable with the little ground pigtail, which did not seem to make an improvement. Disappointing....it was an expensive cable

Tj

Ok - I'm an idiot - your fridge is on the same line as your system right? I don't mind asking stupd questions ONCE!! My circuit consists of just the wall outlets. Just tell me there is no other way for 'gremlins' to get in!!!

 

[Craig]

Just trying to help you trouble shoot the problem by trying the easiest tests first. However that's hard to do without the sub in your possesion.

I'm not sure if the balanced connection would work properly when using a cheater plug on the power cord. Although, I would expect a properly grounded circuit (the powercord is properly grounded) to effectively eliminate Ground Loop when using the balanced connection. Just one more reason for using balanced connections.

If the Descent sub is the only component in your system with a 3 prong plug and everything else is 2 prong then you can expect a loud humm to come through the sub when that is added to the system. The accumulation of all the funky ground related noise from your ungrounded components plus the coaxial cable for your TV is all being drained to your grounded sub like a magnet.

Ok - I'm an idiot - your fridge is on the same line as your system right? I don't mind asking stupd questions ONCE!! My circuit consists of just the wall outlets. Just tell me there is no other way for 'gremlins' to get in!!!

The first step to recovery is admitting you have a Ground Loop Interference problem!

 

[timm]

Couple of updates - the sub is ON ITS way back to me!!! . I think I should have it in possession by around 2pm (seems to be their delivery time). I mis-stated a couple of things. My Odysseys have a 3 pronger as does this monster power strip that I have. I may just bring it straight to the dealer and have him just hook it up. That would definitely answer my question...AND give me a reason to look at inter-connects etc... I can used balanced...sorry if this sounds stupid - should I go balanced given my funky situation if it turns out to be a ground loop issue which I can not resolve other that using the cheater? Or - should the balanced connection eliminate the problem all together and the use of the cheater will not be needed?

 

[JonFo]

Couple of updates - the sub is ON ITS way back to me!!! . I think I should have it in possession by around 2pm (seems to be their delivery time). I mis-stated a couple of things. My Odysseys have a 3 pronger as does this monster power strip that I have. I may just bring it straight to the dealer and have him just hook it up. That would definitely answer my question...AND give me a reason to look at inter-connects etc... I can used balanced...sorry if this sounds stupid - should I go balanced given my funky situation if it turns out to be a ground loop issue which I can not resolve other that using the cheater? Or - should the balanced connection eliminate the problem all together and the use of the cheater will not be needed?

Balanced might resolve the issue if the problem is largely a magnetically induced buzz, but if it is indeed a nasty ground loop issue, then it probably wont and the only way to fix it is to ether use an isolation transformer (which I recommended in post #3) or by ensuring that both the sub and main gear have common grounds.

Borrow a balanced cable and test in your home, if it fixes it, then pay for the cable. If not, then order the Jensen transformer.

 

[timm]

Ok - Never deny the board!!! Ground loop - cheater plug....DONE!!!! My back was killing me - I had fedex just plop it in my car. I brought it to the dealer - they did notice a crease in the front grill - so I am getting that re-placed - they were writing it up - said come back in two weeks and I asked them to plug it in.... no problem - no buzz whatsoever. So, I brought it home - unpacked it -had a cheater plug about 20 feet from where the sub was...and it fixed it. I just couldn't believe that I was getting that type of hum from a ground loop and the bass was so lacking.

Now it is time to play. It sounds great - plenty adjustments abound. Thank you EVERYONE!!!! You are all smarter than you look!!!

 

[Craig]

Timm,
I'm really glad you finally got it working. Now go enjoy it. Someday, I'll add a Descent or Descent i to my system as well.

You are all smarter than you look!!!

If you ever saw us you would know, that's not saying a whole lot


Have a Great New Year!
Craig

 

[billman1965]

Is mine a ground loop?

I will try the cheater plug ASAP!

Symptom:
My grotto rumbles like low thunder while my pre/pro has power. It still puts out bass during music and soundtracks, but while not in use it rumbles.

I will try the cheater plug, and post back.

Happy New Year!
Bill

 

[timm]

I will try the cheater plug ASAP!

Symptom:
My grotto rumbles like low thunder while my pre/pro has power. It still puts out bass during music and soundtracks, but while not in use it rumbles.

I will try the cheater plug, and post back.

Happy New Year!
Bill

I tell you - based on what I heard - it didn't seem like it was the issue...yet it was.... so I would definitely try it. If I would have had the sub in hand (fedex had taken it back) - and got the suggestion - I would have tried it immediately. I put the spikes on yesterday - it just seems like it was too simple setup wise. I have it set up going into the line levels w/ the x-over at 40 hz. Stereo listening sounds great as do movies....There are so many options/hookups I can use - I just gotta keep plugging away until I find something I think is the best.... but right now - I don't know if it gets much better. I feel like I have speakers with the transparancy /highs and mids that I am used to w/ a low end that is clean / tight and I think could rival anything out there. that is a tough combo to beat... (odysseys/descent) thx. tim.

 

[Craig]

By the way, I recommend using the cheater plug only for troubleshooting or as a temporary solution. You should do some further testing up the chain until you can locate the source of the ground loop. There are supposed to be some devices on the market that help but I don't know much about them. Perhaps someone else on this forum does.

 

[JonFo]

As Craig says, the cheater plug is for diagnostics only!

Do some more troubleshooting of the source. Disconnect the cable TV feed (a common source of ground loops). If that's it, then order a Jensen VRD-1FF.

If it's anything else, then get the other Jensen isolator I recommend in post #3. Like I said there, guaranteed to fix the issue.

Cheers,

 

[Dominick22]

I also had this issue with the Descent abd remedied it the same way after calling ML direct. They suggested the cheater plug to me and said that it will in now way adversly affect the subs performance. They said it "could be" used as a permanent fix.

Dominick

 

[JonFo]

OK, time to go on a rant here.

[Rant On]

Why is it that most sub manufactures don’t get the fact many, if not most sub installs will be done in such a way as to be susceptible to a ground loop, or at a minimum, some induced noise?

The fix is to provide an isolation transformer *in the sub* on the inputs (balanced or otherwise).
For $3K subs, you’d think that a $50 part that would guarantee it would *always* work right would be a no-brainer. But no, very few bother and instead let people bang their heads against walls, live with humming subs, or just plain return one and buy another brand that happens to not be susceptible to their particular issue.

Plus many don’t even bother to address the issue in their installation instructions. Heck, just putting in a few recommendations such as the ones covered in this thread (and countless others in AVSForum) would be a good place to start. Even links to third-party products to solve the issues would be nice a well.

[Rant Off]