Humming noise - How to ground a VCR?

[xdcdx]

Hello,

I capture from an external tuner in my VCR and I get a low but annoying humming noise in my captures, I read this might be due to a improperly grounded VCR, is there an easy way to ground a VCR unit? What other problems might cause the humming?

Best regards,
xDCDx

[scharfis_brain]

Pull out the antenna cable from the RF-connector at the back of your VCR.

this should solve your 50/60 Hz humming problem.

[xdcdx]

I don't understand, I am trying to capture from the VCR tuner, how I am supposed to tune something if I pull out the antenna cable? Or did you mean anything else?

By the way, I connect my VCR to my BT878 card via a SCART to composite video cable.

[scharfis_brain]

then, you have either to break all gorund connections of your PC to the power line and external devices, so the only ground connection remains the antenna cable.

as alternative, you can build an RF adaptor cable, that is cut in half. both open ends are then connected via two capacitors. One for the signal, and the other one for ground. this will result in a ground loop break -> no humm.
(in German, this is sometimes called "Mantelstromfilter")

on of those methods is needed to get rid of the ground loop, which causes the humm.

[xdcdx]

Thanks for the info, but could you possibly elaborate more in building the RF adaptor cable?

Do you mean putting two capacitors in the middle of the antenna cable? Are not there different kind of capacitors types? If yes, which one should be used? Will this cable be suitable for connecting to a regular TV afterwards?

[Capmaster]

It's more likely you have an open ground than a ground loop.

Ground loops are usually caused by multiple grounding points in the presence of higher currents. Video signals have only microamps of current and the higher currents exist internally in the unit, and on the AC line. Higher currents do not flow from unit to unit.

An open ground will cause the humming. What I suggest you do is substitute a good cable for your interconnects one at a time. A common culprit is one with RCA connectors.

Eventually the ground can either go bad in the cable at the strain points, or the connection on the outside of the connector can fall prey to contaminants like skin oils attacking the metal and discoloring it - corrosion is a common culprit in bad connections - especially in high humidity;)

Another common cause is the blades of the RCA connector getting looser from repeated matings. A slight squeeze with a pair of pliers will tighten them.:)

[jggimi]

:goodpost:

[Arachnotron]

A nice site with info about ground loops (and other grouding related problems) and links to numerous other sites about this subject can be found here (http://www.epanorama.net/documents/groundloop/index.html)

[edit]

The circuit sharfi was talking about can be found here (http://www.epanorama.net/documents/groundloop/antenna_isolator_building.html)

[Pyscrow]

Originally posted by xdcdx
Hello,

I capture from an external tuner in my VCR and I get a low but annoying humming noise in my captures, I read this might be due to a improperly grounded VCR, is there an easy way to ground a VCR unit? What other problems might cause the humming?

Best regards,
xDCDx

If your VCR is double insulated, earthing it may be illegal, if not dangerous.

[scharfis_brain]

Pyscrow: why this?
the VCR gets (badly, of course) earthed, when pluggin in the RF-Cable.
and it gets earthed, too if you try to connect it to your PC.

[scharfis_brain]

found the images of my RF-DeHumm-Adaptor-[tm] :) , I made about a year ago:


the adaptor (I only had a scanner [no digicam], so the image quality is bad)
http://home.arcor.de/scharfis_brain/samples/Antenne-Kabel.jpg

the wiring scheme (which is nearly the same like Arachnotron's link shows):
http://home.arcor.de/scharfis_brain/samples/Antenne-Schaltbild.png

[Pyscrow]

Originally posted by scharfis_brain
Pyscrow: why this?
the VCR gets (badly, of course) earthed, when pluggin in the RF-Cable.
and it gets earthed, too if you try to connect it to your PC.

Yeah, thats right, but as I said (at least in Australia) if you earth something that has been double insulated, it is illegal.

But as you noted it is "somewhat" earthed anyway, thats why I said "not dangerous". (Or no more than standard anyway:D )

[scharfis_brain]

btw.: what marks a double insulated device?
is it the non-existant earthing (which is supplied by the 3rd connection = ground)?

[xdcdx]

Thanks for all the useful info, guys. :)

[Soulhunter]

Gah, some time ago I had the same problem... (http://forum.doom9.org/showthread.php?s=&threadid=80567) :rolleyes:


Bye