My Descent is humming - cable?

I have a ML Descent run by a Carver Surround Preamp. The sub is 25 feet from the preamp and is humming badly. I have the cheapest possible cable and know that has to be some of the issue. When I disconnect the cable, the sub quits humming. I can't shorten the cable because of how the room is set up. I think I need a much better cable. The preamp has a single rca jack for the sub out and I'm running that to the lft jack in the back of the sub. I would rather not spend over a hundred bucks or so. I'll spend more if necessary. I've been told that 14 or 12 gauge is a good idea as well as using a full freq range, magnetically shielded cable. Any more ideas? Where is the best place to get this type cable?

The cable may be your problem, but more likely it is not. The most probable issue is that you have a ground loop. Do a search on this forum for "ground loop" or "hum" and you should find many threads discussing this problem and ways to diagnose and treat it.

I have found that Descents are very susceptible to ground loop issues. A quick way to diagnose this problem is to buy a "cheater" plug that converts the three-prong plug to a two-prong plug. If using this adapter makes the hum disappear, then you definitely have a ground loop issue and no new cable will fix that.

Also, for quality, reasonably priced cables, I always recommend Blue Jeans Cable. Here is the link:

http://www.bluejeanscable.com/

After Troubleshooting

I've taken everything out of the loop one at a time. Plugged the sub into the same wall socket as the preamp. The hum is the same. I unplugged the rca cable from the preamp and when I put my finger near the cable lead, I could manipulate the hum. I'm thinking its the cable. I'm going to give a 25 foot BJC LC-1 Subwoofer Cable a shot. They talk about humm quite a bit. I'll report the results. I already know the price was right $38!

The search feature is your friend!

John Denison said:

I've taken everything out of the loop one at a time. Plugged the sub into the same wall socket as the preamp. The hum is the same. I unplugged the rca cable from the preamp and when I put my finger near the cable lead, I could manipulate the hum. I'm thinking its the cable. I'm going to give a 25 foot BJC LC-1 Subwoofer Cable a shot. They talk about humm quite a bit. I'll report the results. I already know the price was right $38!

Click to expand...

I had the same issue - as did others...I too unplugged everything - and still hummed.... the cheater plug fixed it...

John Denison said:

I'm thinking its the cable. I'm going to give a 25 foot BJC LC-1 Subwoofer Cable a shot.

Click to expand...

John,

That is a great cable and I am sure you will enjoy it, but I doubt it will fix your hum. I am almost certain you have a ground loop issue. Try the cheater plug.

I am not a fan of cheater plugs; the ground prong is there for a reason - safety ! Once the use of the cheater determines that there IS a ground loop, it should be removed and the source of the ground loop investigated. I admit it's not easy; I once spent two days looking for the source of a ground loop in a power amp I built, but I did find it.

You can also try completely disconnecting your TV cable from the system. TV cable typically uses a completely different grounding system than the home wiring ground system. It's often the root cause of ground loop humm. There are also some inexpensive devices to plug into that eliminate ground loop. I know JohnFo posted a source for one of these.

Also, just because the sound and level of the hum changes when you touch the cable doesn't mean it's the cable. Your just changing the grounding characteristics of your system by touching the cable with your finger.

Subs are sensitive to ground loop because they play well and amplify the lower frequencies like the 60Hz freqs from American AC elec systems or 50Hz elsewhere.

If the new cable doesn't fix the hum problem at least you'll be able to eliminate that in your troubleshooting. $38 for a sub cable is great deal for a sub cable. That's one cable I wouldn't go high-end (AKA expensive) with.

And like Rampage mentioned, "The search engine is your friend". There are many more threads on the dreaded and annoying "ground loop" on this forum.

If all else fails try this ! http://www.ebtechaudio.com/humxdes.html


Ground Loops are a inherent situation with subs.

“The Hum X filters out unwanted voltage and current in the ground line that cause ground loop hum while simultaneously maintaining a solid, safe ground”

I’m confused!! Most electrical noise filters send the noise to ground. Where is the Hum X filtering it to?

Been using the new audioquest Sub3 on my descent with great results...

I had this problem as well. I thought it was the cable, then upgraded to Audioquest Sub3 and it still hummed. Then I just switched to the high input instead of the sub in and the problem is gone.

Cherian said:

“The Hum X filters out unwanted voltage and current in the ground line that cause ground loop hum while simultaneously maintaining a solid, safe ground”

I’m confused!! Most electrical noise filters send the noise to ground. Where is the Hum X filtering it to?

Click to expand...

Its all ball bearings these days !...........

Check older threads on the Descent noise issues. There is a situation where wires, normally hooked to the inside top of the unit, can come loose and pick up a hum from one of the internal circuit boards. Originally suggested by Jim Powers at M/L and has been found on more than a few units.

Tj

The cheater plug didn't fix it. I'll try the new cable and if that doesn't work, I'm planning to try one of the "ground loop" gadgets.

Hum Free at Last!

God bless the BJC LC-1!! It eliminated all the hum I was upset with. I can still hear the sub working, but I have to get right down on it. 90% of the hum disappeared. Thanks to those that helped.

Congrats, John. I am glad that worked for you. I will eat crow now because I was convinced the cable wouldn't fix it but the cheater plug would. Just goes to show, every time you think you have it figured out . . .

Cool. Glad you got it fixed. Throw that old cable in the garbage.

New Cable

I'm almost ready to let things be. Blue Jeans Cable was fast and the cable was much more substantial than I thought a $38 would be.

I also learned that plugging the power cord for the sub into the same surge protector as the aquarium caused some hum. I've plugged the sub straight into the wall now and its considerably quieter. I almost have to do zen to hear it now. What kind of surge protector should I be using?

I've tried the cheater plug and it didn't make any difference. Does that mean I don't have a ground loop issue? Do the Calrad Isolation Transformer - $25 and the Hum X - $90? the same thing? My guess it they burn the noise off with heat?

Hi Guys!
Acquired Descent i recently. Has a bit of amp hum which gets worse when the signal cable is connected, probably partly a ground loop. No luck with Hum-X & cheater plug. Tried to open the back panel to see if anything was loose but there is another plate sealing the inside of the sub, can I remove it to get to the inside of cabinet to see if any wires are touching the amp? I am also looking at Jensen SUB-1RR as well as DCI spec ALH1 to get rid of ground loop. Has anybody had any experience with either of these units?
Thanks,
Vinod.