spdif input circuit help

burbeck · 13th May 2005, 04:19 PM

hi
has anyone got a circuit 75 R spdif consumer to ttl levels, i have been using this one but having problems with oscillation (elekor design i think) tried using different versions of the ic.
regards
bob

paologatto · 13th May 2005, 05:40 PM

http://www.epanorama.net/documents/audio/spdif.html

Check there..

Bye,
Paolo

Jocko Homo · 13th May 2005, 07:19 PM

Reduce R18 to 1 K. Reducing it past that probably won't help much. Get rid of C12. Make sure that it is the HCU04 version.

Some guys say that it has a tendency to oscillate with no input......I never had problems. Bypass, bypass, bypass. Keeps leads short.......etc.

Jocko

jobstens · 13th May 2005, 09:22 PM

Hi !

1st make sure that it is 74hc_U_04
The U stands for unbuffered. each inverter is just a komplimentary fet-pair. with R2 X5 is driven to his working point (yes it's analog !)
2nd the circuit should work fine :-)

i use the same circuit without R18 and without C12.
Some people vary R18 between 0 - 10K, some people use a 10k resistor from output X5 to ground ...

telefunken use in his DA1000 a transformer with a transistor after instead.

There are many ways :-)

Regards

Jobstens

Jocko Homo · 13th May 2005, 09:38 PM

Leave R18 in. The open-loop gain of an inverter is usually around 20 or so. Some may be a bit higher, but 50 is definitely the upper limit. Lowering it after a certain point buys nothing. Except:

Taking it out will lower the input Z. While 1K in parallel with 75R won't throw it off too much, 2K will lower it less.

Jocko

burbeck · 13th May 2005, 11:11 PM

thanks guys, i have played around with this circuit as described no joy. i was hoping that someone would offer a totaly new design
bob

gmarsh · 14th May 2005, 12:07 PM

I've built this and it's stable...

New SPDIF input circuit.

Warning though, it doesn't get full Jocko approval.

I have no idea how much jitter the circuit adds - I'm thinking/hoping that hysteresis-induced phase noise is up in the MHz region, which a CS841x loop filter can eliminate and an AD189x ASRC can completely destroy. One of these days I'll feed the output of it back into the AP System Two and measure it.

300_baud · 14th May 2005, 02:24 PM

Hi Gmarsh,

I built Elso's spdif input circuit with the ad8561 and it seems to work well. Have you compared yours to his circuit and how is it different/better?

Thanks,
300_baud

Jocko Homo · 14th May 2005, 03:31 PM

I don't know why you had trouble with it. An 'U04 inverter is only a pair of CMOSFETs tied together. It doesn't get much simpler. Did you use the right one...........i.e., unbuffered?

I have other circuits, but probably more than a noob wants to futz with.

Yes, Elso's circuit does work. But the diodes start to conduct, and that throws off the actual impedance that the signal sees.

We won't discuss hysteresis. Been done before. Although we would like to see if someone can measure its effect.

Jocko

300_baud · 14th May 2005, 04:32 PM

hi Jocko,

Can you post some spdif input schematics that you would recommend even if they are more difficult to assemble? I wouldn't mind trying them out.

Thank,
300_baud

13th May 2005, 11:11 PM	#6
burbeck diyAudio Member Join Date: Aug 2004 Location: Ratae Coritanorum	thanks guys, i have played around with this circuit as described no joy. i was hoping that someone would offer a totaly new design bob __________________ regards bob

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13th May 2005, 05:40 PM	#2
paologatto diyAudio Member Join Date: Jun 2004 Location: Italy	http://www.epanorama.net/documents/audio/spdif.html Check there.. Bye, Paolo

13th May 2005, 07:19 PM	#3
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	Reduce R18 to 1 K. Reducing it past that probably won't help much. Get rid of C12. Make sure that it is the HCU04 version. Some guys say that it has a tendency to oscillate with no input......I never had problems. Bypass, bypass, bypass. Keeps leads short.......etc. Jocko

13th May 2005, 09:22 PM	#4
jobstens diyAudio Member Join Date: Jun 2004 Location: near Hannover	Hi ! 1st make sure that it is 74hc_U_04 The U stands for unbuffered. each inverter is just a komplimentary fet-pair. with R2 X5 is driven to his working point (yes it's analog !) 2nd the circuit should work fine :-) i use the same circuit without R18 and without C12. Some people vary R18 between 0 - 10K, some people use a 10k resistor from output X5 to ground ... telefunken use in his DA1000 a transformer with a transistor after instead. There are many ways :-) Regards Jobstens

13th May 2005, 09:38 PM	#5
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	Leave R18 in. The open-loop gain of an inverter is usually around 20 or so. Some may be a bit higher, but 50 is definitely the upper limit. Lowering it after a certain point buys nothing. Except: Taking it out will lower the input Z. While 1K in parallel with 75R won't throw it off too much, 2K will lower it less. Jocko

14th May 2005, 12:07 PM	#7
gmarsh diyAudio Member Join Date: Apr 2004 Location: Halifax, NS, Canada	I've built this and it's stable... New SPDIF input circuit. Warning though, it doesn't get full Jocko approval. I have no idea how much jitter the circuit adds - I'm thinking/hoping that hysteresis-induced phase noise is up in the MHz region, which a CS841x loop filter can eliminate and an AD189x ASRC can completely destroy. One of these days I'll feed the output of it back into the AP System Two and measure it.

14th May 2005, 02:24 PM	#8
300_baud diyAudio Member Join Date: May 2004 Location: Toronto, Canada	Hi Gmarsh, I built Elso's spdif input circuit with the ad8561 and it seems to work well. Have you compared yours to his circuit and how is it different/better? Thanks, 300_baud

14th May 2005, 03:31 PM	#9
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	I don't know why you had trouble with it. An 'U04 inverter is only a pair of CMOSFETs tied together. It doesn't get much simpler. Did you use the right one...........i.e., unbuffered? I have other circuits, but probably more than a noob wants to futz with. Yes, Elso's circuit does work. But the diodes start to conduct, and that throws off the actual impedance that the signal sees. We won't discuss hysteresis. Been done before. Although we would like to see if someone can measure its effect. Jocko

14th May 2005, 04:32 PM	#10
300_baud diyAudio Member Join Date: May 2004 Location: Toronto, Canada	hi Jocko, Can you post some spdif input schematics that you would recommend even if they are more difficult to assemble? I wouldn't mind trying them out. Thank, 300_baud

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