projects:hifi:retrofitting_coaxial_spdif_out
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| projects:hifi:retrofitting_coaxial_spdif_out [2022/09/24 01:43] – [Some theory: Impedance matching for a resistor voltage divider network] admin | projects:hifi:retrofitting_coaxial_spdif_out [2024/10/24 12:41] (current) – admin | ||
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| ====== Retrofitting coaxial spdif out ====== | ====== Retrofitting coaxial spdif out ====== | ||
| - | This page describes how to add to a device | + | This page describes how to add to a device |
| The modification described on this page is to add a coaxial spdif output to a Sony MDS-JE520 MiniDisc deck. Although it contains both an optical and coaxial spdif input, it only contains an optical spdif output. The lack of a coaxial spdif output is inconvenient and this modification mitigates that. | The modification described on this page is to add a coaxial spdif output to a Sony MDS-JE520 MiniDisc deck. Although it contains both an optical and coaxial spdif input, it only contains an optical spdif output. The lack of a coaxial spdif output is inconvenient and this modification mitigates that. | ||
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| | //Schematic of spdif coax interface// | | //Schematic of spdif coax interface// | ||
| - | The schematic is in essence an impedance matched voltage divider. Since the transformer has a 1:1 ratio, the signal is AC only and the three inverter driver outputs U1A, U1B and U1C are all identical, the schematic can be simplified for calculation. | + | The schematic is in essence an impedance matched voltage divider. Since the transformer |
| - | S/PDIF signals are defined in IEC 60958-3 (2003)((Digital audio interface, Part 3)). The output shall have a substantial resistive impedance of $(75\ \pm\ 15) (\Omega)$ when measured at frequencies from 0.1 MHz to 128 times the maximum frame rate, which equals to about 5.6 MHz with a sample rate of 44.1 kHz. The signal amplitude shall be $(0.5\ \pm\ 0.1 ) {\text V}$ peak-to-peak, | + | S/PDIF signals are defined in IEC 60958-3 (2003)((Digital audio interface, Part 3)). The output shall have a substantial resistive impedance of $(75\ \pm\ 15) (\Omega)$ when measured at frequencies from 0.1 MHz to 128 times the maximum frame rate, which equals to about 5.6 MHz for a sample rate of 44.1 kHz. The signal amplitude shall be $(0.5\ \pm\ 0.1 ) {\text V}$ peak-to-peak, |
| Based on the definition above, we have two considerations to take into account: (1) Adapt the output voltage to match 0.5 v and (2) make sure the output impedance matches $75\ \Omega$. But since the output level is specified at a $75\ \Omega$ load, the actual voltage divider need to double the output, since half of the voltage is dissipated in the load resistor. | Based on the definition above, we have two considerations to take into account: (1) Adapt the output voltage to match 0.5 v and (2) make sure the output impedance matches $75\ \Omega$. But since the output level is specified at a $75\ \Omega$ load, the actual voltage divider need to double the output, since half of the voltage is dissipated in the load resistor. | ||
projects/hifi/retrofitting_coaxial_spdif_out.1663976609.txt.gz · Last modified: 2022/09/24 01:43 by admin
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