Dull AV question, S Video and hum?

[timbo]

Hi All

I've just had to get a new dvd player as the old one died. No big deal here as I'd been expecting it to go for a little while. Anyway I decided to try an S video cable instead of the old scart lead.

So I swapped out the dead dvd player, slipped in the new, reconnected and yep, its a dvd player, look at the pretty pictures. So its time to try the s video cable and yep, the picture is different, would'nt say better. But theres a hum coming from the speakers. So everything gets switched off, and I check all the connections. OK everything seems to be in order. So switch it all back on, and the hum returns. Ok no problem, I've got a few ferrite ring thingies sitting around, lets try them on the power leads - no difference. Fine there's no analogue connection between the dvd player and the AV amp, the only indirect connection is phono leads from the sky box to the AV amp, and the hum is there on all settings.

So I disconnect the S video cable and the problems gone.

I'm not too fussed as the scart is perfectly adequate, but I'm confused, as the only connection between the dvd player and the av amp is optical, how or where was the noise coming from, assuming it was from the telly via the s video.

Very dull I know but I'm intrigued to say the least.

Timbo

PS forgot to add the dvd is marantz the av is yamaha and the telly is sony.

 

[michaelab]

An earth loop of some kind would have been my immediate suspicion but if you say that neither the TV nor DVD player are connected to the AV amp electrically than that doesn't seem possible. No idea otherwise

Michael.

 

[julian2002]

isn't the outer metal bit of the svideo plug a ground for the lead? i'm not that familiar with svideo but suspect there would be a ground connection somewhere.
cheers

julian

 

[Mr Perceptive]

HUM........

I got a similar hum through my Naim Pre/Power everytime the DVD player connected on (in Standby or Bypass). The hum was audible with any input selected on the Naim. I initially thought of earth issues (my DVD is only a two wire jobbie) and I made up leads to connect the DVD chassis to the Naim Star Earth, but the hum persisted. (BTW I don't get a similar hum from my Skybox)

In the end I routed the DVD player through the FM Tuner input of my Arcam DAB Tuner which is relay switched, and the hum has gone. Obviously the DVD is now only connected to the Naim when Tuner is selected and the Arcam DAB is in Bypass mode.

Weird, but since its dissappared, I've stopped investigating.

Mr Perceptive

PS The hum was present at various times of the day on several days so I didn't think it was a mains related issue

 

[timbo]

Originally posted by julian2002
isn't the outer metal bit of the svideo plug a ground for the lead? i'm not that familiar with svideo but suspect there would be a ground connection somewhere.
cheers

julian

Julian

Yes I think that the plug outer is the ground, so I can just about believe that interference fro the telly could get to the AV via the dvd when it's on, but it also came thru when the skybox input, and the same thing cured it. That's what confused me. Particularly as its a two lead wire.

The first suspect was an earth loop, which as I've never had one with all the bits of kit at home surprised me, so I've tried them from different sockets with no change in result. So the blame is definately pointing to the telly as being the source of the noise, but I still have no idea as to how the noise is being transmitted. I'm happy to take Mr Perceptive's route as I've solved the problem.

Timbo

 

[technobear]

How close is the telly to the DVD player. And what is between the two. Separation may be the order of the day.

 

[I-S]

Separation is indeed the key. There's a very good chance that your DVD has a frame transformer in it, and this produces a LARGE field, which is likely inducing the hum into a nearby cable or component.

As for the video connection, S-video is generally not regarded as being as good as an RGB SCART connection. For the mathematically minded:

DVI > VGA > RGB Component >= RGB SCART > S-Video >> Composite (either through scart or standard composite lead).

Obviously not many home cinema setups can be used with DVI or VGA (although some plasma screens, projectors and LCD TVs can take such inputs, few sources have outputs in these formats).

Of course, YMMV and all that, so by all means give whatever connections you can use a go.