SPDIF coupling caps

lucpes · 24th July 2004, 08:18 AM

I have a DAC that uses two 10nf caps for SPDIF coupling. What should I use for those - I tried so far WIMA FKP2 - too dark sounding and WIMA MKS02, which seems to be too harsh and 10nf ceramics which are 'dirty sounding'. Guess MKP or MKTs (low dielectric loss caps/good HF & pulse behaviour) would fit the bill better?

Jocko Homo · 24th July 2004, 08:37 AM

Well, part of it depends where they are in the circuit.

If they connect directly to the input, a lot of the sonic characteristics will be because of reflections.

I would expect ceramics to not sound good, although their lower inductance would be a benefit.

Jocko

roibm · 24th July 2004, 09:50 AM

I had about the same and I just removed them. Since the source is a good device, I don't need them anymore.
Do you really need them? As far as I know the perfect coupling caps are no caps

lucpes · 24th July 2004, 02:41 PM

Here's the schematic right out of the datasheet.

@roibm: are you sure they are safe to remove? The transport device is transformer coupled.

lucpes · 24th July 2004, 02:43 PM

Forgot to attach...

MalichiConstant · 24th July 2004, 03:01 PM

Use a good metalized polypropelyne cap (MKP) with the lowest voltage you can get to keep the cap physical small. You can go to higher values and 0.047uF would be fine. I use some of the ERO 100V MKP caps to AC couple 75 load like the input of pulse transformers. Always put a cap in front of a pulse transform. I have heard a few 100 uA screw the sound of the pulse tranformer up big time when driving it with a video amp with a DC offset in the low millivolt range. NO DC CURRENT THROUGH THE PULSE TRANSFORMER! One of the Black Gate 0.1 uF nonpolar electrolytics also sounded extremly good in the digital interface.

lucpes · 24th July 2004, 10:28 PM

Actually I meant that I have a transformer on the transport side and these grr... problematic caps on the DAC side.

So these ought to be ok? http://uk.farnell.com/jsp/endecaSear...=3038543&N=401

Jocko Homo · 24th July 2004, 10:48 PM

If you are only going to use a transformer on one end, make it the RX end.

Kepping the outer conductor on th TX will reduce radiation, although there are ways around that. Besides, the RX side will perform better if you use a differential input, and the best way to do that is with a transformer.

Jocko

jewilson · 24th July 2004, 11:44 PM

There nothing wrong with using a CKO5 style NPO, COG or even X7R ceramic material capicator in this application. There are many more areas of TX and RX interface to cause problems that those caps. However, make you use low inductance caps.

Jocko, he can elaborate on all the pit falls in the SPDIF interface. You might even get him to sell you a an impedance matched design the has been spectral tested. Then you won't have to get concerned about the caps and poor designs that plague 99.9% of all SPDIF interfaces.

My sermon is over for at least week, till some one asks the same questions again.

roibm · 25th July 2004, 12:47 AM

Quote:

Originally posted by lucpes
@roibm: are you sure they are safe to remove? The transport device is transformer coupled.

Well, in my case, I got no transport, it comes from the computer and I trust it. If I'll get problems, then I'll learn a lesson too

24th July 2004, 08:18 AM	#1
lucpes diyAudio Member Join Date: Dec 2003 Location: Iasi	SPDIF coupling caps I have a DAC that uses two 10nf caps for SPDIF coupling. What should I use for those - I tried so far WIMA FKP2 - too dark sounding and WIMA MKS02, which seems to be too harsh and 10nf ceramics which are 'dirty sounding'. Guess MKP or MKTs (low dielectric loss caps/good HF & pulse behaviour) would fit the bill better? __________________ Deep down inside.

24th July 2004, 02:41 PM	#4
lucpes diyAudio Member Join Date: Dec 2003 Location: Iasi	Here's the schematic right out of the datasheet. @roibm: are you sure they are safe to remove? The transport device is transformer coupled. __________________ Deep down inside.

24th July 2004, 03:01 PM	#6
MalichiConstant Account Disabled Join Date: Jul 2004 Location: Fort Worth Texas	Size matters and smaller is often better! Use a good metalized polypropelyne cap (MKP) with the lowest voltage you can get to keep the cap physical small. You can go to higher values and 0.047uF would be fine. I use some of the ERO 100V MKP caps to AC couple 75 load like the input of pulse transformers. Always put a cap in front of a pulse transform. I have heard a few 100 uA screw the sound of the pulse tranformer up big time when driving it with a video amp with a DC offset in the low millivolt range. NO DC CURRENT THROUGH THE PULSE TRANSFORMER! One of the Black Gate 0.1 uF nonpolar electrolytics also sounded extremly good in the digital interface.

24th July 2004, 10:28 PM	#7
lucpes diyAudio Member Join Date: Dec 2003 Location: Iasi	Actually I meant that I have a transformer on the transport side and these grr... problematic caps on the DAC side. So these ought to be ok? http://uk.farnell.com/jsp/endecaSear...=3038543&N=401 __________________ Deep down inside.

24th July 2004, 11:44 PM	#9
jewilson diyAudio Member Join Date: May 2002 Location: Plano , TX	There nothing wrong with using a CKO5 style NPO, COG or even X7R ceramic material capicator in this application. There are many more areas of TX and RX interface to cause problems that those caps. However, make you use low inductance caps. Jocko, he can elaborate on all the pit falls in the SPDIF interface. You might even get him to sell you a an impedance matched design the has been spectral tested. Then you won't have to get concerned about the caps and poor designs that plague 99.9% of all SPDIF interfaces. My sermon is over for at least week, till some one asks the same questions again. __________________ Jim W.


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24th July 2004, 08:37 AM	#2
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	Well, part of it depends where they are in the circuit. If they connect directly to the input, a lot of the sonic characteristics will be because of reflections. I would expect ceramics to not sound good, although their lower inductance would be a benefit. Jocko

24th July 2004, 09:50 AM	#3
roibm Banned Join Date: Dec 2003 Location: Transylvania	I had about the same and I just removed them. Since the source is a good device, I don't need them anymore. Do you really need them? As far as I know the perfect coupling caps are no caps

24th July 2004, 10:48 PM	#8
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	If you are only going to use a transformer on one end, make it the RX end. Kepping the outer conductor on th TX will reduce radiation, although there are ways around that. Besides, the RX side will perform better if you use a differential input, and the best way to do that is with a transformer. Jocko

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