Cable related hum - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 22nd May 2005, 02:07 PM   #11
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
http://www.partsexpress.com/pe/showd...number=180-075
  Reply With Quote
Old 22nd May 2005, 02:47 PM   #12
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi K-amps,
As you have proved empirically, the hum DOES come from the cable ground, which is the worlds largest ground loop. Use 1:1 balun transformers to isolate the cable ground. The better quality ones have lower losses. I had to service all kinds of gear due to ground tracks being blown ... to the video jacks. Hmmmm, not warranty.

The largest amount of destruction I have ever witnessed in a lightning strike occurs every single time when cable is involved. I will not have cable in my house for that reason. Do use the three wire grounded outlets.

-Chris
  Reply With Quote
Old 22nd May 2005, 03:05 PM   #13
SM2GXN is offline SM2GXN  Sweden
diyAudio Member
 
Join Date: Dec 2004
Location: Northern Sweden
Send a message via ICQ to SM2GXN
http://www.partsexpress.com/pe/show...tnumber=180-075

That's the way to go, this is nothing more than 2 coupling caps 10nF, one for the center conductor and the other screen.
It's wise to not only break up the screen of the coax because even the center conductor is grounded through the input circuit of the rf amp in the tuner. I can't come up with any reason why this could attenuate the rf.
This is a very common problem, hum on audio hum bars on tv caused by a groundloop.

I agree with John10

Quote:
I think K-Amps hum problem may be caused by a ground loop created by the ground difference between house wiring ground and the cable system ground.
Björn
  Reply With Quote
Old 22nd May 2005, 03:07 PM   #14
diyAudio Member
 
Join Date: Nov 2002
As Chris and DJK have pointed out the problem of hum is caused by the cable coax. This problem is eliminated by the usage of an issolation transformer such as the one DJK has left a link to.
  Reply With Quote
Old 22nd May 2005, 03:25 PM   #15
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi SM2GXN,
The ones I use are 1:1 RF transformers. Complete isolation. Better brands will offer very low losses. I haven't seen the capacitor types in a long time. Same thing goes for splitters and attenuator taps. Use good stuff or the quality really goes down.

-Chris
  Reply With Quote
Old 22nd May 2005, 05:25 PM   #16
diyAudio Member
 
Join Date: Apr 2003
Location: New York
I used the partsexpress isolator. This one attenuates the
signal. I get breakup of my digital cable signal. HBO
does not show at all.

I'm trying to use caps in the shielding side only. What kind of caps
would you use (Ceramic disk? Film?).

Thanks

Harry
  Reply With Quote
Old 22nd May 2005, 07:07 PM   #17
SM2GXN is offline SM2GXN  Sweden
diyAudio Member
 
Join Date: Dec 2004
Location: Northern Sweden
Send a message via ICQ to SM2GXN
Hi Chris!

I agree, if you by it's better to stay with better brands. A good 1:1 RF transformer shouldn't be lossy.
Anyway the signal at the tv jack is usually between 60-80dbmV so
a couple of db loss will do no harm as long as it doesn't go much below 60dbmV.

Quote:
I'm trying to use caps in the shielding side only. What kind of caps
I use ceramic disc caps they will do the job.

Bjorn
  Reply With Quote
Old 22nd May 2005, 08:03 PM   #18
diyAudio Member
 
Join Date: Apr 2003
Location: New York
It's very sensitive. I just tried a single cap on the shielding.
It does get rid of the noise but also of the signla for some
channels. Again some of the premium channels drop.

I'm considering using the digital audio out. Are there cheap
decoders for sale?

Thanks

Harry
  Reply With Quote
Old 22nd May 2005, 09:09 PM   #19
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi Harry,
You need to totally isolate the signal or you may toast some tuners. There may be a DC path due to an RF input transformer or coil. Any gear between the cable ground and local earth ground is at risk of being totally blasted. Just depends on the ground differential of the next lighting strike.

-Chris
  Reply With Quote
Old 23rd May 2005, 12:22 PM   #20
diyAudio Member
 
Join Date: Apr 2003
Location: New York
The tuner is property of the cable company. Of course
the signal can go through my pre amp.

Luckely we are in New York City. Lightning is not frequent
and there are many high buildings around. I think the
problem stems from insufficient grounding. The cable
comes from the roof and services many apartment
buildings. The installation is done pretty poorly.

As a follow up: I did try to ground it by connecting it
to the outside of my metal electrical duckts. That
reduced the hum somewhat but when I listened to the
DVD the hum was there. I disconnected the cable box but
the hum remained. It's able to send the hum through the
ground to the stereo.

Everthing I try to do gives a poorer image quality. I'm wondering
if I have a marginal cable signal? I wonder how I can
verify that? Upstairs strangely enough I do not have a hum.
They are connected through a different cable run. I also have
different gear (I'm using a Maranz HT receiver). Downstairs
I'm using my own pre-amp and Cary tube gear.

I'm wondering if it's possible to buy a cheap DVD player and
modify it so it can work as a Dolby decoder? Then I can put
a filter on the ground of the digital input and I would have clean
sound. If we get a power surge it would only blow the cable
box and maybe the filter.

Harry
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Anyone using microphone cable in making their phono cable? rich121 Analog Line Level 8 10th September 2010 12:50 AM
cheap cat5e cable for speaker cable fishline Full Range 6 19th May 2009 07:42 PM
DAC-related reading anli Digital Source 0 26th February 2009 08:17 AM
New in package Component Video Cable and Toslink Cable for sale cheap jainbaby Swap Meet 1 30th December 2007 05:18 PM
problems with speaker cable as power cable pjpoes Parts 11 14th January 2007 08:24 PM


New To Site? Need Help?

All times are GMT. The time now is 11:39 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2