Digital Cable

Due credit is paid to the Max Rochlin Memorial Cable, which I read over on the Enjoy the Music homepage before making my own. I opted for a slightly scaled down, simpler approach :


Canare LV-61S. 75 Ohm RG-59/U type coax cable, with a bare copper braided shield and bare copper stranded center conductor.


Canare makes nice true 75 Ohm connectors, for RG-59/U cable the part number is RCAP-C4A.


click to enlarge diagram

The only trick to making these is getting the appropriate crimp tool used to attach the gold pin to the center conductor. In a pinch solder could be used. Heatshrink over the connector barrel and down 2" or so over the cable.

Digital cables are used to connect digital sources to a seperate DAC or A/V receiver. There are three common interfaces, optical fiber (Toslink), 75 Ohm coaxial (spdif) and 110 Ohm balanced (AES-EBU). Coax is generally considered superior to optical fibres, while the AES-UBU is only common in pro gear. Given the choice between coaxial or optical, choose coax. Differences between various cables are reported to be slight to insignificant, so it certainly isn't worth agonizing over. Just keep the following guidelines in mind :

  • Digital information is carried over frequencies of many MHz. This in many times higher than audio, and as a consequence the characteristic impedence of the cable is important. spdif digital cables should be coaxial, with a 75 Ohm impedance, good shield coverage and low capacitance. This is also the recipe for video cable, so RJM Digital Cable is also ideal for video applications!

  • There is some debate whether using true 75 Ohm RCA connectors is of any use when the impedance of typical RCA panel jacks are not anywhere near 75 Ohms. In my opinion given the high quality and low price of the Canare connectors, there is no reason to use anything else.

  • Keep the cables short! If the run is less than 1 m, and you've cleared the above two points on cables and connectors, its time to move on to sections of your audio system more worthy of attention.