Technical question - CD transports

[montesquieu]

An impedance matching question on CD transports ...

I notice that the Audio Note transports have output transformers on the digital out, one assumes to manage the impedance of the connection.

Is this common in transports? If not, how else is it managed (caps?) and would attention to this be beneficial when modding transports? I assume the purpose, as with everything in a dedicated transport, is the goal of jitter reduction.

What should the ideal characteristics of a digital out be, into, say a Young DAC or any other reasonably high-end DAC?

[Stratmangler]

Impedence should be 75 ohms for SPDIF.

[montesquieu]

Yes but my question is why do AN put a transformer on the 75 ohm output? What's the advantage? And is it a mod worth doing to other transports?

[Reid Malenfant]

Galvanic isolation It prevents earth loops & hum so it does have advantages - yes!

[nat8808]

I remember reading somewhere, probably in reviews, that Meridian's transformers on the digital outputs were to help when driving long digital cables..

However, it would also make sense to use a transformer to get that impedance to 75ohms when taking the spdif signal more directly from the chip where it's generated.

A lot of CD players use little amplifier circuits before the digital out which, according to Lukasz Fikus of Lampizator fame (has run a website for years experimenting with CD players and now wow-ing the world with his own dac) degrade the signal trace and really are just an after thought of the circuit designer, mostly following white paper example designs from chip manufacturers like Philips.

He's best spdif output (according to him and his oscilloscope) is to use some kind of valve in between chip and output, perhaps as a cathode follower or something and also providing the correct impedance - apparently Audio Note also now use this idea too.. perhaps the valve output is in their recent designs but used transformers previously?