AW: S/PDIF, was Re: 240volts and ground hum problems.

[Ullrich Peter]

	>I just added a coaxial S/PDIF out to my Sony DTC-790 DAT recorder (has
	>optical out only, but optical and coax in). It was very simple: I just
	>connected the signal from one pin of the optical transmitter via a 390
	>ohms resistor to the output jack. I saw in an old Elrad project that
	>they did it the same way from the output of a 74HC04. Works good. But
	>I'm wondering if I should add anything? Protection zener diodes perhaps?
	>I don't quite see the need for a transformer, since the ground of the
	>coax input is connected to the DAT recorder's ground.
	>Why did Sony leave out this feature if it costs just one resistor and
	>one jack??

	Normally it works fine without an transformer but for preventing hum it is better to
	add one.
	As the special transformer are very expensive I designed my own that only costs
	about $0.30 and works very fine.

	Conrad Electronic in Germany sells little ferrite rings (about 7mm diameter) and you
	just have to make 15 windings on one side and 3 on the other side.
	If anybody needs the circuits (in conjunction with the surrouding circuit and driver) let
	me know and I will scan it. I use it in a universal SPDIF-interface for the Elrad Take Five
	digital audio interface for the PC and in my self built sample rate converter.

	Ciao
	Peter

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                   Ing. Peter Ullrich         mailto:ullrich at kapsch.net
                   Homepage: http://come.to/ullrich    or the full link
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                   Hardware & Software Developer /  Electronic Musician
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