what's the best way to convert SPDIF into CMOS level? - Page 2

Bricolo · 2nd June 2004, 10:22 AM

ok I'll try this

I have some AD8065, are they OK for this use?a

banana · 2nd June 2004, 10:55 AM

Guido,

About the Opamp approah. Do I need to add bias to the SPDIF signal before feeding it to the Opamp? I mean offsetting the "bipolar" +0.25/-0.25V input signal into "single-ended" +2.75/+2.25V, before amplification.

Or should I run the Opamp with +5V single supply and simply clip the output to +5/0V?

Guido Tent · 2nd June 2004, 11:39 AM

Quote:

Originally posted by banana
Guido,

About the Opamp approah. Do I need to add bias to the SPDIF signal before feeding it to the Opamp? I mean offsetting the "bipolar" +0.25/-0.25V input signal into "single-ended" +2.75/+2.25V, before amplification.

Or should I run the Opamp with +5V single supply and simply clip the output to +5/0V?

Hi

Yes, need bias at half of supply voltage

NEVER clip digital signal;s at such important places

regards

carlosfm · 2nd June 2004, 12:01 PM

Guido,

Is the LM6171 a good choice for that job?

Thanks

Guido Tent · 22nd June 2004, 09:23 PM

Quote:

Originally posted by carlosfm
Guido,

Is the LM6171 a good choice for that job?

Thanks

Hi Carlos

should work well - no clue on the sound (all you do there is audible, subtle but audible :-)

regards

dmfraser · 23rd June 2004, 05:18 PM

You can't use most op-amps because the signal is in the 6 MHz range. If the lvel is too high coming from your source, you can attenuate it with a resistor. However, I use a 74AC04 operating on a 3.3V supply to buffer the input on my unit. You don't need anything fancier. On the electrical input, I couple the S/PDIF signal through a DC blocking capacitor to the input of the 74AC04 through a 220 ohm resistor. The input is biased with two resistors to 40% of the supply voltage.

On my opto input, the output of the TORX141 is buffered through another section of the 74AC04.

banana · 23rd June 2004, 05:57 PM

A little sharing, though most of you might already know. TTL gate does not work in the case of U3 on DEM-DIR1701 instruction manual. The first gate is actually a linear amplifier and only CMOS gates are suitable for doing this.

Before I learned this, I tried 74F04 and 74LS04. No matter how I bias the input DC, these TTL gates won't have symmetric output duty cycle. And they don't amplify, instead they simply switch on or off.

Finally, I settle on ADM1485. It's plug and play, trouble free. Thanks Andrei.

23rd June 2004, 05:18 PM	#16
dmfraser diyAudio Member Join Date: Dec 2003 Location: Orange County, CA	S/PDIF Input You can't use most op-amps because the signal is in the 6 MHz range. If the lvel is too high coming from your source, you can attenuate it with a resistor. However, I use a 74AC04 operating on a 3.3V supply to buffer the input on my unit. You don't need anything fancier. On the electrical input, I couple the S/PDIF signal through a DC blocking capacitor to the input of the 74AC04 through a 220 ohm resistor. The input is biased with two resistors to 40% of the supply voltage. On my opto input, the output of the TORX141 is buffered through another section of the 74AC04. __________________ Dan Fraser

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2nd June 2004, 10:22 AM	#11
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	ok I'll try this I have some AD8065, are they OK for this use?a

2nd June 2004, 10:55 AM	#12
banana diyAudio Member Join Date: Feb 2003 Location: Hong Kong	Guido, About the Opamp approah. Do I need to add bias to the SPDIF signal before feeding it to the Opamp? I mean offsetting the "bipolar" +0.25/-0.25V input signal into "single-ended" +2.75/+2.25V, before amplification. Or should I run the Opamp with +5V single supply and simply clip the output to +5/0V?

2nd June 2004, 12:01 PM	#14
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	Guido, Is the LM6171 a good choice for that job? Thanks

23rd June 2004, 05:57 PM	#17
banana diyAudio Member Join Date: Feb 2003 Location: Hong Kong	A little sharing, though most of you might already know. TTL gate does not work in the case of U3 on DEM-DIR1701 instruction manual. The first gate is actually a linear amplifier and only CMOS gates are suitable for doing this. Before I learned this, I tried 74F04 and 74LS04. No matter how I bias the input DC, these TTL gates won't have symmetric output duty cycle. And they don't amplify, instead they simply switch on or off. Finally, I settle on ADM1485. It's plug and play, trouble free. Thanks Andrei.