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My goal is to convert optical audio signal - Toslink - to S/PDIF coaxial input signal. The frequency is up to 96 KHz. I'm thinking about Toshiba TORX179L optical receiver. According to the datasheet, the output of TORX179L is 0,2V low, and 4V high level voltage. My question is - do I have to use some repeater like 74HCU04 here: enter image description here

Or can I directly connect TORX179L to S/PDIF coaxial input? The circuit will be built inside the player.

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  • \$\begingroup\$ What do you mean with "S/PDIF input"? \$\endgroup\$
    – CL.
    Nov 8, 2016 at 10:31
  • \$\begingroup\$ I mean S/PDIF RCA coaxial input socket. \$\endgroup\$ Nov 8, 2016 at 10:32

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The schematic shows a TORX173/176 which is confusing.

It also makes it look like the TORX modules have more than 3 pins yet these modules have only 3 pins: vdd, data and gnd, also confusing !

I believe the TORX modules already have some inverter like circuits build-in so adding inverters (the 74HCU04) seems somewhat pointless to me.

I build such a thing once, I did not include the inverters but I did include a 100 nF capacitor (using 3 x 47 nF is silly) and the resistive divider. As long as you do not have a very long Coax cable between this circuit and the SPDIF input, I expect this to work fine. Mine did anyway :-)

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  • \$\begingroup\$ Yes, I think so too. The TORX179L will be mounted near RCA input, so the wire length will be very short. \$\endgroup\$ Nov 8, 2016 at 10:38
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The datasheet suggests that the TORX device cannot drive a 430 ohm load (see the Abs Max Iout) though it's overall pretty vague (I can't see the specified load for the VOut specification). Whether you need 2 stages of inversion is another matter - the S/P-DIF format comes from AES/EBU which was designed to work equally well inverted or not.

So I believe you do need some sort of buffer stage of adequate bandwidth - well over 6 MHz to support 96kHz sample rate. @FakeMoustache says otherwise - perhaps he used a different optical receiver, or perhaps these work considerably better than the spec, but according to the datasheet, it isn't guaranteed.

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