HELP - Descent hummmmmmmmm

[timm]

Hi all - well it has happened - I got my descent under the tree....Problem...my wife bought it off audiogon - and although the sub looks fantasitic - when plugged in -- all we get is a big hummm... no signal - just hummm... I unplug the lfe cable - and there is no hum. However, I plug this same lfe cable into my paradigm sub - and there is no problem. I plug into the line level left and right - and get the same thing. Any thoughts? Any idea on the cost of the fix? sounds like a loose wire to me...probably from shipping. Do we have a Ross in the house (previous owner). thanks tim.

 

[Pcar928fan]

I can't WAIT to hear the fix for this! My descent has ALWAYS done that too! Not a loud hum for me though. If fact if I turn the vol down to a lower level you have to really get close to the sub w/ nothing on to hear it. As an example in my case, if the refridgerator comes on in the kitchen (connected to the main listening room) it is WAY louder than the Descent when it is set at a normal Movie level (which is a bit louder than a music level).

SOOO, I can't wait for the fix on this! Mine when left on "auto" never shuts off either...well, let me say the blue "M" never goes off anyway! I thought it was a problem, but the shop I bought it from did not seem much interested in helping. The first BIG hum I got with it was due to the cable company. I had to put a filter on the cable between the wall and the cable box. Now I am on Sat but still have the slight hum.

PLEASE, PLEASE, PLEASE advise on this matter!

Hi all - well it has happened - I got my descent under the tree....Problem...my wife bought it off audiogon - and although the sub looks fantasitic - when plugged in -- all we get is a big hummm... no signal - just hummm... I unplug the lfe cable - and there is no hum. However, I plug this same lfe cable into my paradigm sub - and there is no problem. I plug into the line level left and right - and get the same thing. Any thoughts? Any idea on the cost of the fix? sounds like a loose wire to me...probably from shipping. Do we have a Ross in the house (previous owner). thanks tim.

 

[JonFo]

Bummer, you both have ground loops.

Just because one sub exhibits it and not the other does not mean it’s not a loop. A lot depends on the way the amps in the subs are designed and assembled.

A short term thing to try is to ensure the sub is plugged into the same outlet group as the pre-amp.
Often a sub is plugged into another outlet near it that could be on a separate phase leg.

The ultimate fix is to use an isolation transformer. Or since the Depth has a balanced interconnect input, to use that if your pre-has balanced outs

The Jensen SUB-1RR is guaranteed to fix the problem. Not the cheapest at $115, but like I say, guaranteed.

 

[roberto]

Bummer, you both have ground loops.

Just because one sub exhibits it and not the other does not mean it’s not a loop. A lot depends on the way the amps in the subs are designed and assembled.

A short term thing to try is to ensure the sub is plugged into the same outlet group as the pre-amp.
Often a sub is plugged into another outlet near it that could be on a separate phase leg.

The ultimate fix is to use an isolation transformer. Or since the Depth has a balanced interconnect input, to use that if your pre-has balanced outs

The Jensen SUB-1RR is guaranteed to fix the problem. Not the cheapest at $115, but like I say, guaranteed.

Agreed 100% with ground loop problem. Sometimes, the ground coming from the cable company is the problem. To find out if it is, just disconnect the cable antena from the TV or the first unit that receives the cable...and listen. If the humm is gone, then know you found what was the problem. There are several ground loops fixers...I do like the Tributaries cable...it is expensive, but solve the problem easy here...happy listening,
Roberto.

 

[IWalker]

yep, as they said, ground loop hum. Should be right at 60Hz. I had this in a sub I built because the stereo it was hooked up to had a cable hookup. There are various ground loop transformers you can use. I'd try to use it on the cable line instead of your speakers...but that's just me. This almost surely is NOT a problem with the speaker

 

[Pcar928fan]

yep, as they said, ground loop hum. Should be right at 60Hz. I had this in a sub I built because the stereo it was hooked up to had a cable hookup. There are various ground loop transformers you can use. I'd try to use it on the cable line instead of your speakers...but that's just me. This almost surely is NOT a problem with the speaker

I concur that it is a ground loop. Not sure why though. All of my front end gear (pre, Sat receiver, DVD, CD, Phono pre, etc.) are all on a RGPC Pole Pig and my 3 Rotel amps and the Descent are on a RGPC SubStation. I was hoping all of this would take care of it, but it has not. We did have a Sat reciever problem awhile back w/ one of the cables and it caused a REALLY loud hum, but I didn't notice that the hum went away completely even when the Sat reciever was disconnected completely from the system.

What are the products and brands etc. I should be looking at???

Thanks guys!

 

[timm]

Hold on there partners!! No signal - ONLY hum... no bass - only hum....you still think ground loop problem? thanks to everyone. If it is --cool -- No ground loop issue with my other sub (no ground on this other sub's plug either) - plugged into the same outlet. I would think ground loop if I heard bass coming from the sub ALONG with a hum... Could any of you concur with me that this sounds like a possible internal wire that got jogged loose on the amp during transport???

Anyway - seller is checking with fed-ex and seems to be a real stand-up guy. If it is an issue with the sub - I am positive it happened in transport.

I repeat -- NO BASS SIGNAL.... thanks tim.

 

[Tj Bassi]

I have two Descents in our system, both are connected daisy-chain fashion to a single LFE output. One has always had a slight hum while the other is completely quiet. Both are on the same power circuit. The hum from the one unit is aggrevated when the refrigerator runs, which not on the same circuit. While I agree that a ground loop is probably the culprit, our case suggests that some units might be more prone to the problem than others.
One thing to check, especially if your unit was shipped, is to open the rear cover and make sure the wires leading to the three drivers are suspended from the cabinet top by a little hook. This suggestion came from Jim at M/L. If the wires fall off of the hook they can pick up some noise.

Tj

 

[Tj Bassi]

Timm- Just read your last post.....there are quite a few connectors inside the Descent, so its possible one if them came loose. Somewheres around here I should have photos of the sub's innards......if I can find them I'll try to suggest something to look for.

Tj

 

[timm]

Timm- Just read your last post.....there are quite a few connectors inside the Descent, so its possible one if them came loose. Somewheres around here I should have photos of the sub's innards......if I can find them I'll try to suggest something to look for.

Tj

Thanks Bud... it is very appreciated... happy holidays to all!!!! tim

 

[Tj Bassi]

Timm-I found a few photos but they are hardcopy only. I dont have any way to scan them tonite.
In a nutshell...there are two power supply connections inside the unit using Molex connectors. Probably not the problem since your unit powers up. The LFE jack and L/R jacks are hardwired to the circuit board so they shouldnt be loose.
What I do see is two telephone-type cables that link two of the boards together, and one (or it could be three) cables returning from each of the drivers using a simple RCA-ish jack. I assume these are for the servo control and I recall this connector being easy to remove.
If you turn the sub around, the entire rear metal panel comes off if you remove the hex-head screws....but unplug the unit first
All of these wires will prevent you from fully removing the rear panel...the wires only have so much give. If I recall correctly, the servo wire is so short that you have it remove it first and re-connect it last. It should be apparant if anything is loose at this point.
I can scan this document for you early in the week, or help you walk thru it on the phone if you with.
BTW...the telephone cables connect the front panel controls with the main electronics on the rear.
Hope this helps....

Tj

 

[Tj Bassi]

I was able to scan the wiring diagram, but its a large file at about 3 megs. I'm going to try to resize it and send it to you off-list. The diagram is not in the manual but is something Jim at M/L sent me when I first had problems with one of the Descents.
Perhaps someone on the group with better editing software can resize it and post it somewheres for all to see...?

Tj

 

[timm]

Ok - stupid question... how much of this is hard wired vs 'clipped' on? I am not sure of my abilities with a soldering gun...

In other words - if I crack it open - what are the odds it might be something I just clip on vs have to solder on?

 

[Pcar928fan]

Tim,

Your problem is different than mine I guess. I do get all the bass response I need I just also get a very low level hum along with it. I am virtually sure mine is a ground loop.

Hold on there partners!! No signal - ONLY hum... no bass - only hum....you still think ground loop problem? thanks to everyone. If it is --cool -- No ground loop issue with my other sub (no ground on this other sub's plug either) - plugged into the same outlet. I would think ground loop if I heard bass coming from the sub ALONG with a hum... Could any of you concur with me that this sounds like a possible internal wire that got jogged loose on the amp during transport???

Anyway - seller is checking with fed-ex and seems to be a real stand-up guy. If it is an issue with the sub - I am positive it happened in transport.

I repeat -- NO BASS SIGNAL.... thanks tim.

 

[Tj Bassi]

Looking at the drawing of the Descent MLSIBO board, everything is attached with connectors; nothing is hard-soldered. Also make note that most of the connectors are not interchangable, which means they only go back in one place. The phone and Molex connectors are keyed for correct fit. The drivers are connected with push-on spades so be sure to maintain polarity-red & black wires need to be put back where they came from or the drivers will be out of phase. All three servo connections attach to the board on one connector, which is also keyed for correct insertion.
If one of the wired is off it should be obvious. The interior of the Descent cabinet is wadded full of white stuffing so you'll have to *carefully* poke around to find all of the wiring harness.

Tj

 

[timm]

Tj -- thanks again -- I got the pics/document etc... I will forge ahead - and as I said in my email - this may have to wait till the 26th because of the holidays ...this is KILLING ME!!! But, seeing everything with connectors makes me think....'I can do this.' I think my wife - is more upset than I. I just think I'll be able to figure it out and fix it.... I'll let you all know what happens.....and if I run into any....'uh....what does that thingy do....' I'll send something out..... thanks again my fellow addicts.... tim.

 

[Craig]

Timm, If you have no luck with finding a loose connection then you can always call ML's tech support when they open after the holidays. They are known to be very helpful and supportive even if you're not the original owner.

2101 Delaware
Lawrence, KS 66046
U.S.A.
phone: (785) 749-0133

 

[timm]

thanks craig....

 

[timm]

fyi -- took a look inside - everything looked ok....so it was insured - however, they want to pick it up and look at it - bring it back to their place. I'm sure they have something to hook it to...right. Anyway, I'm going to give them a demo - it looks fine - turns on - etc... It is probably a short somewhere - but I just can't find it...After the struggle for the insurance claim - I will end up bringing it to my local dealer and have them repair it.

 

[jimbo]

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.