Digital Audio Application Notes Electrical SPDIF Output From an Optical SPDIF Output

Electrical SPDIF Output From an Optical SPDIF Output

As professional devices, the Benchmark DAC-104 and the DAC2004 Digital-to-Analog converters have only electrical, not optical inputs. To use a direct feed from a CD player, therefore you need to add an electrical output to the CD or DVD player -- and the sonic quality is well worth the effort. This application note specifically shows how to modify the Sony CDP-XE500 player. The techniques and circuit will work for many other players with optical outputs.

Figure 1. Sony CD Player

Figure 2. Circuit Add-In

Figure 3. Photo Detail of Signal Pick-Off Point

Figure 4. Location of Output Connector

1. Build the matching network according to the schematic using high quality monolithic ceramic caps. We "space wired" ours, that is, we connected the parts together without a circuit board to hold them, using short lead lengths. The BAT85s are low capacitance Schottky diodes made by Philips and available from Future Electronics.

2. You will need to remove the circuit board from the chassis to make some of the connections.

3. Drill the appropriate hole in the chassis. Install an output connector. We used a BNC connector that mounts from the inside of the chassis to simplify installation. You may prefer to use an RCA type output connector.

4. Pick up the digital ground and +5 volts at the rear of the circuit board near the optical transmitter. You will need to remove solder from a couple of unused holes.

5. Solder connection wires in place. The digital output comes from the end of L205 as shown. Add the space wired circuit, and reinstall the cover.

6. Plug the system together, sit back and enjoy the breathtaking sonic quality of the Benchmark Digital-to-Analog converters.