Go Back   Home > Forums > Source & Line > Digital Line Level

Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 8th June 2009, 02:10 PM   #1
Josuah is offline Josuah  United States
diyAudio Member
 
Join Date: Nov 2006
Default S/PDIF Lock Noise

Let me start by saying I manufacture and sell a commercial DAC. I browsed the forum rules and didn't see anything forbidding participation in this capacity, but if I missed something please let me know. I found references to noise in general from a forum search, but nothing that looks like my specific problem.

I am having an issue where when the audio signal is first sent from the transport, my DAC outputs a brief crackle or noise. I am not 100% sure if the music is present or not during this time. This only happens with a couple of transports out of many, and only when the signal goes from off (not even a silent signal) to on. It sounds similar to if you forcibly create a poor optical connection by not fully connecting the optical cable and wiggling it around. It occurs with both optical and coaxial connections.

The noise does not occur during playback and is clean for the duration of the signal lock, and it does not occur with the vast majority of transports.

Any help?
  Reply With Quote
Old 8th June 2009, 05:52 PM   #2
Josuah is offline Josuah  United States
diyAudio Member
 
Join Date: Nov 2006
Default DC Offset Adjustment

The noise is due to DC offset adjustment. I believe the typical solution is to use a coupling capacitor at the analog signal output. But I was hoping there might be another solution that does not require me to introduce any components in series with the analog signal.
  Reply With Quote
Old 9th June 2009, 08:08 AM   #3
Hurtig is offline Hurtig  Denmark
diyAudio Member
 
Join Date: Feb 2005
Location: Denmark - Århus
I don't think this problems is caused by DC offset...

I would guess that you use CS8416 as SPDIF receiver. With the CS8416 you can see these kind of noises with some CD-drives.
If you have a lock indicator, you will see that this will flash when you hear the noise.
I is causes by these CD-drives, that does not send real SPDIF signal when not in paly-mode, and will stop as soon as it starts to play.
Typically you have connected the lock signal from CS8416 to your DAC-chip mute/RST input. And then the DAC-chip will go in and out of mute/RST along with the flashing lock indicator. And this generates the noise.

You can remove this by NOT letting the DAC-chip go into mute/RST or maybe by using a delay between the lock signal and the mute/RST on the DAC.
  Reply With Quote
Old 9th June 2009, 05:42 PM   #4
Josuah is offline Josuah  United States
diyAudio Member
 
Join Date: Nov 2006
Thanks for the reply. I'm using a WM8804 to PCM1794A. I do indeed see the signal lock indicator fluctuate. But I have not wired the signal lock to the PCM1794A mute. The mute is always off.

I experimented with wiring it so the signal lock would trigger mute, but I haven't yet been able to confirm this fixes the problem. It sounds like from what you're saying it may actually cause a problem. I thought about adding a delay, but that would mean you miss some music.

I can see the analog output DC level change on my oscilloscope when this happens. It looks like it drops and then comes back up.
  Reply With Quote
Old 9th June 2009, 06:16 PM   #5
Hurtig is offline Hurtig  Denmark
diyAudio Member
 
Join Date: Feb 2005
Location: Denmark - Århus
OK....
Anyway, the noise is generated by the SPDIF datastream from the CD-drive. As I said, you can remove this noise by adding some kind of delay in the mute-signal.
Make so that as soon as the lock is lost, the PCM1794A goes into mute, and that the lock must be present for a given period before the PCM1794A is un-muted again. I would think that 250ms om delay will do the job.

How about that PCM1794A?? You like it?? What kind of analog stage are you using?
We did test the PCM1794A, but choose something else ;-)
We found the PCM1794A to be a bit to skinny, even using an well known discrete analog stage. Be we were VERY impressed by the noise performance of the PCM1794A. I have never seen better noise performance from any DAC. Also the mid and the high frequency was impressive. Only the low frequency area had some trouble. But I believe that this could be solved by more tweaking with the analog stage.
  Reply With Quote
Old 10th June 2009, 02:01 AM   #6
Josuah is offline Josuah  United States
diyAudio Member
 
Join Date: Nov 2006
Yeah, I figured mute might be an option, especially with a delay. Thought there might be another solution though.

I really like the PCM1794A. I'm using a completely passive transformer-coupled output stage. It really works well. That is part of the reason I don't want to use a coupling capacitor--I don't want it to contribute any impedance that would affect the output.

Thanks.
  Reply With Quote
Old 10th June 2009, 06:21 AM   #7
Hurtig is offline Hurtig  Denmark
diyAudio Member
 
Join Date: Feb 2005
Location: Denmark - Århus
I fully understand why you don't want to use a capacitor. And I don't believe it will remove the problem.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
S/PDIF Optical to S/PDIF RCA Replacement PrecisionAudio Digital Source 2 11th February 2007 09:35 PM
Signal Lock LED w/ CS8414? fluckscapacitor Digital Source 4 31st July 2005 07:23 PM
Cs8414 Lock LED leo529 Digital Source 1 24th November 2002 01:14 PM


New To Site? Need Help?

All times are GMT. The time now is 11:07 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2