LVTTL to SPDIF

Ardee · 25th August 2007, 09:48 AM

Can anyone advise as to the best way to convert low voltage TTL to SPDIF, please? Quality is more important to me than cost/complexity.

Thanks.

bocka · 25th August 2007, 10:50 AM

Use a 74LV86 (or similar XOR-Gate) to obtain a SOUT and /SOUT signal. Use this differential signal to feed an AD8132 high-speed differential op-amp and use a balun SPDIF output transformer.

novec · 12th September 2007, 05:29 AM

Does this compete with regular DITs like the Burr-Brown DIT4192 from TI? I do like the simplicity of it, and all I need is TTL-S/PDIF buffering, no sample rate conversion or anything.

Ardee · 12th September 2007, 07:45 AM

I think the DIT4192 converts I2S plus user bits to SPDIF. My question was how to convert LVTTL SPDIF to something which will drive a 75ohm interface.

Thanks for the suggestion bocka , btw.

novec · 12th September 2007, 11:39 AM

Of course, my bad.

rfbrw · 12th September 2007, 12:37 PM

Quote:

Originally posted by Ardee
My question was how to convert LVTTL SPDIF to something which will drive a 75ohm interface.

CLC001

nonoise · 12th September 2007, 10:48 PM

Just keep in mind that the output level should be 500mv P-P into 75 Ohm +/- 20% This is if you prefer to keep to the standard (IEC60958-3)

gmarsh · 13th September 2007, 01:44 PM

Use a 5V powered HCT gate (74HCT04, Tinylogic chip, etc) to convert LVTTL to +5V CMOS. You can use a faster logic family (VHCT, ACT) but be careful with decoupling.

On the output of the gate, put a 0.1uF series ceramic capacitor for DC blocking, then a resistor divider of a 330 ohm series and 100 ohm shunt.

(Actually, re-arrange that - put the 330 ohm resistor directly at the output pin of the logic gate, followed by the series capacitor and 100 ohm shunt.)

This gives you a 1.5Vpp unloaded, 0.75Vpp loaded SPDIF output with a near-75-ohm source impedance.

25th August 2007, 09:48 AM	#1
Ardee diyAudio Member Join Date: Nov 2005	LVTTL to SPDIF Can anyone advise as to the best way to convert low voltage TTL to SPDIF, please? Quality is more important to me than cost/complexity. Thanks.

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25th August 2007, 10:50 AM	#2
bocka diyAudio Member Join Date: Jul 2003 Location: Hannover	Use a 74LV86 (or similar XOR-Gate) to obtain a SOUT and /SOUT signal. Use this differential signal to feed an AD8132 high-speed differential op-amp and use a balun SPDIF output transformer.

12th September 2007, 05:29 AM	#3
novec diyAudio Member Join Date: Aug 2005	Does this compete with regular DITs like the Burr-Brown DIT4192 from TI? I do like the simplicity of it, and all I need is TTL-S/PDIF buffering, no sample rate conversion or anything.

12th September 2007, 07:45 AM	#4
Ardee diyAudio Member Join Date: Nov 2005	I think the DIT4192 converts I2S plus user bits to SPDIF. My question was how to convert LVTTL SPDIF to something which will drive a 75ohm interface. Thanks for the suggestion bocka , btw.

12th September 2007, 11:39 AM	#5
novec diyAudio Member Join Date: Aug 2005	Of course, my bad.

12th September 2007, 10:48 PM	#7
nonoise diyAudio Member Join Date: Jun 2006	Just keep in mind that the output level should be 500mv P-P into 75 Ohm +/- 20% This is if you prefer to keep to the standard (IEC60958-3)

13th September 2007, 01:44 PM	#8
gmarsh diyAudio Member Join Date: Apr 2004 Location: Halifax, NS, Canada	Use a 5V powered HCT gate (74HCT04, Tinylogic chip, etc) to convert LVTTL to +5V CMOS. You can use a faster logic family (VHCT, ACT) but be careful with decoupling. On the output of the gate, put a 0.1uF series ceramic capacitor for DC blocking, then a resistor divider of a 330 ohm series and 100 ohm shunt. (Actually, re-arrange that - put the 330 ohm resistor directly at the output pin of the logic gate, followed by the series capacitor and 100 ohm shunt.) This gives you a 1.5Vpp unloaded, 0.75Vpp loaded SPDIF output with a near-75-ohm source impedance.

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