New guy, new (old) Descent, new problem

[Tj Bassi]

Hi all,

First, my apologies for having been no more than an occasional visitor to this club for about the past year. Finally decided to register and take part in all of the interesting discussions......

I have been doing battle with a new (but older) Descent subwoofer for a few months. The unit was originally purchased by a friend about two years ago from a reputable dealer, but has sat in the box unopened until recently. He sold me the unit,still sealed, which I installed my system (Requests, Cinema, Marantz SR9200, Krell FPB 250m's) and fine it tuned using some of the suggestions from previous threads in this forum.
The sub sounds great, until you turn the processor's volume down, and then you notice the hum eminating from the unit. Not too bad on multichannel music, horrible on 5.1 movie soundtracks when the audio is at a lull.
So far I have tried all the usual fixes and nothing has made an ounce of improvement. It sounds like a ground loop noise, but the hum still exists when you remove the interconnect from the preamp (I am using the single LFE input). An electrician came over and moved some breakers around in the box, but that didnt help. Last call was to MartinLogan themselves, and they offered a hum fix, which was two replacement electrolytic caps for the power supply. That did not work either.
Simply having the signal cable connected to the sub starts the hum (It is a premium cable, however). Connecting it to the preamp makes the hum worse. Before trying ML again, I was wondering if anyone has gone through the same situation. I have never had a hum or strange noise in my system, but this one is killing me.
On another note, the folks at Martin Logan are exceptionally nice to talk to on the phone, same with Krell. Almost unheard of these days.....

Thanks,
Tj Bassi

 

[Reverb2009]

Have you tried hooking up the descent using any of they other available ports on the back of the descent? It could be a problem with the LFE input on the descent.

My Dealer had a customer exchange a brand new descent for another one, because the RCA LFE port was making the descent hum but the other ports did not have this problem.

 

[aliveatfive]

Is the Descent plugged into the same circuit as the preamp? Sometimes this solves that problem. Also, try plugging in the Descent without the ground pin. You can try using a "cheater" plug - that's a 3 pin to a 2 pin converter. They used to be available at hardware stores.

 

[roberto]

Hi all,

First, my apologies for having been no more than an occasional visitor to this club for about the past year. Finally decided to register and take part in all of the interesting discussions......

I have been doing battle with a new (but older) Descent subwoofer for a few months. The unit was originally purchased by a friend about two years ago from a reputable dealer, but has sat in the box unopened until recently. He sold me the unit,still sealed, which I installed my system (Requests, Cinema, Marantz SR9200, Krell FPB 250m's) and fine it tuned using some of the suggestions from previous threads in this forum.
The sub sounds great, until you turn the processor's volume down, and then you notice the hum eminating from the unit. Not too bad on multichannel music, horrible on 5.1 movie soundtracks when the audio is at a lull.
So far I have tried all the usual fixes and nothing has made an ounce of improvement. It sounds like a ground loop noise, but the hum still exists when you remove the interconnect from the preamp (I am using the single LFE input). An electrician came over and moved some breakers around in the box, but that didnt help. Last call was to MartinLogan themselves, and they offered a hum fix, which was two replacement electrolytic caps for the power supply. That did not work either.
Simply having the signal cable connected to the sub starts the hum (It is a premium cable, however). Connecting it to the preamp makes the hum worse. Before trying ML again, I was wondering if anyone has gone through the same situation. I have never had a hum or strange noise in my system, but this one is killing me.
On another note, the folks at Martin Logan are exceptionally nice to talk to on the phone, same with Krell. Almost unheard of these days.....

Thanks,
Tj Bassi

Hola...your problem it is called ¨ground loop¨...many times is due to ground problem...if you unplugg your antenna-cable tv from the tv or vcr, does your problem is solved?...if it is, the potencial difference in grounds makes it to hum, the 60Hz signal is induced....get a transformer for cable antenna at mcmelectronics, cheap solution...happy listening,
Roberto.

 

[Tj Bassi]

The only output (besides splitting the main L/R signal) on my preamp is the LFE channel, although someone suggested purchasing a single-ended -> balanced adaptor and connecting that to the Descent's balanced LFE input. I have not found one of those adaptors, but they must be available somewheres.
We have tried plugging the sub into the same outlet as the preamp, which was our motivation for bringing in an electrician to look over the service panel. That did not help.
As for the 'cheater plugs', I havent tried that, probably should, but removing the chassis ground doesnt sit well with me, as a matter or practice. In doing so, I would expect that the only ground point to the sub would then be provided by the shield in the cable, which is attached to the processor's ground, correct?
Does seem worth a try for now....

Thanks,
Tj

 

[Tj Bassi]

Roberto,

Removing the cable box did not make a difference. In fact, we systematically removed each component from the system to see which one might be the culprit. What a job.....we use the Premier rack with the hidden cable trays, so disconnecting any component is a chore.
We could not find any particular component that was causing the hum.

Tj

 

[KCWolfPck]

I am willing to bet the "cheater plug" solution about will solve your problem. Two other possible solutions:

1) Utilize a XLR interconnect to your sub if your pre-amp supports it.

2) Purchase a sub RCA interconnect that has a ground "tail" at the sub end. An example would be an Audioquest Sub interconnect. They have a little ground cable that you can screw on to your subs chassis.

www.audioquest.com

DIRECTIONS: If you hear noticeable hum in your system after connecting your subwoofer, please attach Sub-3's little extra tails. Some equipment has a ground (GND) connection on the back-panel, if not, attach the little spade lugs to any screw on the equipment chassis of both the source and the subwoofer.

Good luck!

Scott

 

[Tj Bassi]

Very good suggestions; I'll have to try those. My preamp has only an RCA sub output, but I'd like to make up a cable to connect it to the Descents XLR input. Does anyone know the pin configuration of the Descent XLR connector?

Tj

 

[Peter Hogan]

Hi,
Try here for XLR adapters:

http://www.audiogear.com/Audio-Adapters-Xlr.html

Peter

 

[lexor]

descent hum

do you by any chance have any room light dimmers switches in your room? i ran into this problem with my depth subs and grotto. i took them out and the subs are quiet and the hum went away.. good luck

 

[nsgarch]

Tj, I haven't read all the responses above. Certainly lifting the AC plug ground on all components except the preamp/processor is the standard way of achieving "star grounding." However, I was struck by your comment "Simply having the signal cable connected to the sub starts the hum." Without going into a long explanation of "why" (if this works, I will) try reversing the signal cable, even if that means the "arrow" is pointing in the "wrong" direction. Let me know what happens.

Neil

 

[Tj Bassi]

To answer the above two posts, yes...we have two dimmers installed within 10 feet of the sub's position, but they dont seem to be the cause of the noise. Neil asked about reversing the cable, which is something I havent tried yet but its worth a shot. I also spoke to Jim Powers today at ML and he suggested checking to see if the shield of the RCA connection is indeed electrically connected to the units back panel.
One thing is clear, with so many good suggestions offered by forum members, I decided to take all of them and put them on a spreadsheet, that way I can systematically take note of the cause/effect of the various 'fixes', and determine which one actually solves the problem.
Tuesday or Wednesday evening will be dedicated to subwoofer experiments, hopefully I will have some information to share with the group. I'd do it tonite, but on Monday my wife gets home late so I have a few hours to throttle the system to my hearts content without receiving any flak
Or as our next door neighbor puts it...."My peas keep bouncing up and down on my fork"

Thanks for the suggestions-Tj

 

[Tj Bassi]

Maybe a quick fix? Using the cheater plug gets rid of the hum from the drivers, although there is still a buzz that can be heard if you lay your head down on the top of the cabinet....Can anyone else hear a slight buzz through the top of their Descent? This particular noise is not bothersome, its just that I noticed it.
The light dimmers in the room do not seem to be inducing the hum. I shut the lighting circuit to that room off and the buzz was still there prior to installing the cheater plug.
On the plus side, the illuminated "ML" logo looks trick in the dark

Tj

 

[aliveatfive]

Tj -

FWIW - I get an almost inaudible buzz on my Depth if it is plugged into a separate cicuit and I'm listening through my pre-pro. It does not, however, intrude on my music or HT listening.

 

[Reverb2009]

Can anyone else hear a slight buzz through the top of their Descent? This particular noise is not bothersome, its just that I noticed it.

I do not get any hum or buzz from by Descent, it is dead quiet.


Check the link out I posted below and see if this is worth a try for your situation. It is PS Audio's hum buster, It is not cheep but could fix your problem. If it does not work for you, you have 30 days to send it back for a full refund. Also Ps Audio hum busters pop up on Audiogon.com from time to time, you may be able to save a few buck there.

http://www.psaudio.com/products/upchbmoreinfo.asp

Upc-200HB

Improved video performance
Improved audio performance
Clean and pure AC power
Reduces or eliminates internal hum
100% protection from power problems
Nearly 100% efficient
Cleaner, quieter sound
Improves efficiency
Quiets the listening room



Good Luck

 

[Robin]

Sounds like a power cord contact problem...

Tj,

Welcome to the ML Club...

I had a hum problem with my Descent, in the beginning. I use the RCA subwoofer jack, to my AV Reciever preamp./processor...
When, I first installed, my Descent, unfortunately, I had a hum... I tried everything systematically, ruling out one thing, then another. Like you have done... Nothing really worked... Until finially, I tried plugging the Descent into a seporate circuit, all-by-it-self, with it's own surge protector. That worked some, but the hum was not completely gone, especially at high subwoofer volume, sound familiar?
So then, in addition, to having it's own circuit (surge protector), what finially, completely stopped the hum, was when, I moved the Descent's power cable completely away from the front (main's) speaker cables, so they could not touch at all (absolutly no contact) with the front (main's) speaker cables.
Poof..., no more hum...

Hope this works for you...

Cheers

-Robin

 

[zaphod]

I had a hum problem ... what finially, completely stopped the hum, was when, ...

hmmm, i would have suspected that Robin's solution would have involved suspending the sub from the ceiling...

 

[Robin]

I was trying to avoid a head injury...

zaphod,

I concidered it!

It was only because, I didn't want the Descent to fall down and go boom..., on my head..., all hunderd pounds of it... I found another way... Remember, that necessity is the mother of invention...

Cheers

-Robin

 

[Reverb2009]

Remember, that necessity is the mother of invention...

And what go's up must come down.

 

[Robin]

As long as it doesn't come down on my head...

Joe,

Let me get out of the way first...


-Robin