View Full Version : S/PDIF inputs : capacitor or transfo coupling ?

2009-03-10, 09:25
My satellite receiver has a S/PDIF RCA connector. No optical connector, alas, you'll see why :
It is SCART connected with my TV set, which has some ground leaks (up to 70 V!). I have had some problems with the analog link to my amplifier...

- Is the transformer-coupled S/PDIF input of the Transporter "floating" enough ?
- Do i need some sort of insulation transformer ?
- In that case, what stuff ? (impulsion xformer ?)
- More generally, are there some audible difference between the BNC and the RCA inputs, or is it simply a convenient way to switch between different inputs ?

Edit : checked with a multimeter : BNC grounds are not connected to the chassis. RCA are.

2009-03-10, 10:10
If you're worried about ground loops, use either Transporter's BNC or optical input. The BNC is floating, and is transformer isolated so it can't make a loop. The optical, of course, is optically isolated.

I don't follow what you're saying about the SCART connector. It is normal to measure significant differences in signal ground between two devices, if either of them does not have an earth ground. This is not a bad thing per se. If the equipment is properly designed then the signal cable establishes the ground reference between them. Once they are connected, the difference in voltage should disappear.

2009-03-11, 10:56
Thank you very much for your answer.
I did not expect an answer from the father of the Transporter !

In my setup, it is not a real problem of ground loop : in fact, my cathodic TV has a big default current (maybe from the high voltage transformer) and it is not grounded : I have measured 70V between chassis and ground. When I used an analog audio cable, the leak was returning to ground via my amplifier and has burnt some lo-value resistors (between chassis and mains grounds).
I know : I only need to get my TV set repaired ;-)

2009-04-17, 08:34
I have just finished my SP/DIF cable, with the right connectors : Cinch (sat TV tuner) and BNC (to the floating input of the Transceiver).

It works (only) when "source clock" is on this input. Logical...

But when I switch to the Squeezecenter, I hear muffled and "bassy" sounds.

I have tried "sync" and "async" options in the menu, but it does not change anything : in other words, when I want to switch between the BNC input and the SQcenter, the only way that I've found is to change the clock input via the settings of the SQcenter.

Unless I am wrong with the setup, would not it be more convenient to choose the clock source for each input ?