HELP - Descent hummmmmmmmm

[Pcar928fan]

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.

Jonathan,

Tell me what this isolation transformer is. Got a web link to it. I would like to try it...well, first I will try the cheater plug.

I use a Richard Gray Power Station SubStation that all my amps and the sub are plugged into and I would have thought that would have isolated it enough. That was part of the reason I bought the thing in the first place figuring that it would cure the hum...though my hum is very slight (it is VOLUME dependent though, so you can turn the sub and the HUM up anytime you want, but when the sub is at normal vol levels for regular movie and audio listening you don't hear it when the music is on or you are sitting in the normal listening location.)

Thanks guys (and gals)! Love this forum!

 

[IWalker]

http://www.smpstech.com/mtblog/isolation_transformer.html

informative link on the subject of isolation transformers.

 

[jtwrace]

great article IWalker.

You can also talk to Dick McCarthy at RG. I have found him to be very helpful with problems.

http://www.richardgrayspowercompany.com/contact/index.html

 

[Craig]

I use a Richard Gray Power Station SubStation that all my amps and the sub are plugged into and I would have thought that would have isolated it enough.

I'll bet that your coax video cable isn't going through that power conditioner.

Because the cable TV works off a seperate ground system it is probably the most common cause of ground loop. Try disconnecting your cable and see if the humm goes away. If so, then the $10 part from the "Jensen" website that someone posted earlier in this thread may be all that you need.

 

[Pcar928fan]

I'll bet that your coax video cable isn't going through that power conditioner.

Because the cable TV works off a seperate ground system it is probably the most common cause of ground loop. Try disconnecting your cable and see if the humm goes away. If so, then the $10 part from the "Jensen" website that someone posted earlier in this thread may be all that you need.

I think you are correct. The worst hum I ever had was one time when one of the two lines from the sat down to the receiver had been disconnected. I am certain that is the source of my trouble!

So the $10 Jensen part is the link to follow then I bet...I'll check it out!

Thanks to all!

 

[Kruppy]

If coax is the problem.....

I think you are correct. The worst hum I ever had was one time when one of the two lines from the sat down to the receiver had been disconnected. I am certain that is the source of my trouble!

So the $10 Jensen part is the link to follow then I bet...I'll check it out!

Thanks to all!

Pcar928fan,

Ahhh, that $10 Jensen part is actually $115. Pricey little buger, but having followed JonFo's posts on the site for quite some time, he knows what he's talking about.

I don't know about the capabilities of your Monster Conditioner, but if your coax cable is the problem you rmight want to check this out. I had a very bad ground loop problem and another member here (Spike and I believe DTB300) sugested I try the following:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=180-075

The best $10 I ever spent.

 

[Pcar928fan]

Thanks to all. i actually have one of those "in line" "filters" that I will hook up. My concern is that it might effect my reception of some sat channels. They always seem iffy in the first place!

I'll keep you all posted...

Pcar928fan,

Ahhh, that $10 Jensen part is actually $115. Pricey little buger, but having followed JonFo's posts on the site for quite some time, he knows what he's talking about.

I don't know about the capabilities of your Monster Conditioner, but if your coax cable is the problem you rmight want to check this out. I had a very bad ground loop problem and another member here (Spike and I believe DTB300) sugested I try the following:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=180-075

The best $10 I ever spent.

 

[JonFo]

Jonathan,

Tell me what this isolation transformer is. Got a web link to it. I would like to try it...well, first I will try the cheater plug.

I use a Richard Gray Power Station SubStation that all my amps and the sub are plugged into and I would have thought that would have isolated it enough. That was part of the reason I bought the thing in the first place figuring that it would cure the hum...though my hum is very slight (it is VOLUME dependent though, so you can turn the sub and the HUM up anytime you want, but when the sub is at normal vol levels for regular movie and audio listening you don't hear it when the music is on or you are sitting in the normal listening location.)

Thanks guys (and gals)! Love this forum!

Pcar928, I see Iwalker beat me to the answer on what in iso-transformer is, that’s a great article.

The fact that you have a slight hum is one reason I so heartily recommend an iso-max of some kind on the subs. Many installs have great power systems (as you do), and yet have some form of induced or loop hum.
Induced hum can really only be addressed by using balanced connections, and also a great reason for balanced power (my rig is all balanced, both power and cabling where possible).
Loop hum requires an isolation device to break the loop. Here’s the link:

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

The Sub1 listed above is for when you have a purely audio equipment induced ground loop.

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

...

For Video induced ground loops, the VRD-1FF is the champagne budget solution, the parts express (or rat shack equivalent) are the beer budget solutions. The Jensen has the best bandwidth (less interference or side-effects), which is why I recommend their products.
You pretty much need one or the other, but on a few occasions, I’ve seen people actually need both but that’s rare.

 

[timm]

Wow - I didn't know this was like a flu bug I passed on.....Thanks for all of the great input and help. I will give a post on my impressions of the sub once I play with it some more.

 

[Handyman]

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.

I recently purchased a Depth, and upon hooking it up, had the dreaded 60 Hz hum emanating from the drivers, which I assumed was a ground loop. I spent hours troubleshooting (interconnects, cheater plugs, etc.) to no avail. Finally, I disconnected everything from the Depth except the power cord, and lo-and-behold, it still hummed, even without any input. Searching the forum for a possible cause, I found this thread. For lack of any other reasonable alternative, I checked the issue described Tj's post. Sure enough, the wires from all three drivers were out of the clip at the top of the cabinet, laying down by the toroidal transformer inside the bottom. Trying to rehook them in the clip, it was clear that the clip was too small to actually hold more than one of the three wires, so I used a cable tie to fasten them up securely. Put everything back together, and like magic, the hum was gone. (There's still a normal faint trace of mechanical hum from the transformer itself, but nothing coming out of the drivers.)

It's hard to believe that a >$1000 device could be so handicapped by a $0.10 part. Had I not discovered this thread, I would have returned the product. Somebody at M/L needs to make a real simple change on the production line to prevent the wires from ever falling down.

Sorry for dusting off an old thread, but I am now a happy M/L owner, thanks to Tj and the Martin Logan Owners Club.

 

[Tj Bassi]

Glad you got the problem resolved. I would guess that if you have a Depth/Descent with a hum, 98% of the time its a ground loop thing, but the droopy driver wire situation comes up once and a while.
I have one Descent that picks up a slight buzz when the fridge is running. And NO, its not on the same circuit as the fridge. Go figure that one out (!)

Tj

 

[benleeys]

I wonder if any of you guys are experiencing a hum problem with the new Descent i. I have been living with it on mine for the last 6 months or so. It is quite unoticeable at mid volume but at full volume, the RS meter will read about 80dB from a foot away.

I have gone thru all that have been written in these pages, but the problem seems to be related to the design of the old Descent and, as far as I can figure out, is not applicable to the i.

 

[Handyman]

I wonder if any of you guys are experiencing a hum problem with the new Descent i. I have been living with it on mine for the last 6 months or so. It is quite unoticeable at mid volume but at full volume, the RS meter will read about 80dB from a foot away.

Just to clarify, on the problem with the fallen driver wires inside my Depth (non-i), the hum I had did not change with the volume setting. Power on: hum; power off: no hum. Apparently, the power transformer was directly inducing it into the wires, without any involvement of the amplifier section.

 

[Pcar928fan]

I wonder if any of you guys are experiencing a hum problem with the new Descent i. I have been living with it on mine for the last 6 months or so. It is quite unoticeable at mid volume but at full volume, the RS meter will read about 80dB from a foot away.

I have gone thru all that have been written in these pages, but the problem seems to be related to the design of the old Descent and, as far as I can figure out, is not applicable to the i.

My regular Descent is that way...I have not bothered to try the Jensen ground loop breaker. If I unplug the LFE input the hum stops, so I know it is a pass through problem. I have tried the Sat receiver and that is not it now (a worse hum was associated w/ that). As you said at a mid volume level that is good for 2 channel (maybe even a little loud for 2 channel) and good for action movies you won't even notice it if something else is making noise (or the movie/music is playing) but if you turn it up w/ nothing playing you will REALLY hear it! SUCK!

 

[benleeys]

My regular Descent is that way...I have not bothered to try the Jensen ground loop breaker. If I unplug the LFE input the hum stops, so I know it is a pass through problem. ......SUCK!

Just to further clarify situation, the hum on my i is there even without any input connected. It's just there when you connect only the power. Cannot be a ground loop too, since there is no ground connection in the power cord on this model. I can only suspect it to be an induced hum, since I've checked all connections. By the way, the wiring really sucks. It's all over the place, unshielded, and loose clips which I had to tighten with a pair of sharp-nosed pliers. Further, power carrying lines were bunched up together with signal lines. Wonder what sort of QC they have at ML. Sorry for the rant, but am sorely disappointed with ML at this point in time.

Ben

 

[Pcar928fan]

Yea Ben I understood your post. Just pointing out that it is not unusual to have something causing a hum. Mine is different from yours, but still annoying.

 

[Handyman]

I wonder if any of you guys are experiencing a hum problem with the new Descent i. I have been living with it on mine for the last 6 months or so. It is quite unoticeable at mid volume but at full volume, the RS meter will read about 80dB from a foot away.

Just to further clarify situation, the hum on my i is there even without any input connected. It's just there when you connect only the power.

If you're getting a hum as loud as 80dB with no inputs connected, and it varies with the volume control, it sounds to me like you've got a bad amplifier in the sub. Did your unit have this problem when it was new, or did it just develop the problem six months ago?

 

[benleeys]

If you're getting a hum as loud as 80dB with no inputs connected, and it varies with the volume control, it sounds to me like you've got a bad amplifier in the sub. Did your unit have this problem when it was new, or did it just develop the problem six months ago?

The hum came with the unit direct from ML. I hope you're right, Handyman. Anyway, my dealer has given up fiddling with it and is having a replacement shipped. Expected to arrive early this week. Wish me luck with the new one.

 

[benleeys]

Handyman,

After a good night sleep, I just remembered. The i has got 3 amplifiers in it, one for each of the woofers. Since all 3 woofer units hum ..... it will have to be an amp design fault. Then why are we not hearing from other i owners?

 

[Handyman]

After a good night sleep, I just remembered. The i has got 3 amplifiers in it, one for each of the woofers. Since all 3 woofer units hum ..... it will have to be an amp design fault. Then why are we not hearing from other i owners?

How does one volume knob control all the amps? If there is some type of preamp section shared by all three, perhaps that's where the problem is.