Dumb Question re "locking" of DAC to digital input

You folks were so helpful with my question about an input transformer that I hope you won't mind another question, this time one which probably qualifies as dumb.

I have a CD transport (Cambridge CXC) connected to the SPDIF input on my DAC using a coaxial cable. I normally leave the transport and DAC turned off when not in use, and when I want to listen I turn on the transport first, then the DAC. Twice now, after turning on the power, there was no signal output, no sound from either channel. The solution in each case was to turn off the DAC, let it sit for a minute or so, and then turn it on again. Everything then worked normally.

Is this a case of the DAC not "locking" onto the transport output? Is it normal for this to happen occasionally?

I don't recall this happening when I had an Audio Note Kit 3.1 DAC a few years ago, but I didn't use the CXC transport with the ANK for very long.
 

MikeyFresh

Moderator
Staff member
You folks were so helpful with my question about an input transformer that I hope you won't mind another question, this time one which probably qualifies as dumb.

I have a CD transport (Cambridge CXC) connected to the SPDIF input on my DAC using a coaxial cable. I normally leave the transport and DAC turned off when not in use, and when I want to listen I turn on the transport first, then the DAC. Twice now, after turning on the power, there was no signal output, no sound from either channel. The solution in each case was to turn off the DAC, let it sit for a minute or so, and then turn it on again. Everything then worked normally.

Is this a case of the DAC not "locking" onto the transport output? Is it normal for this to happen occasionally?

I don't recall this happening when I had an Audio Note Kit 3.1 DAC a few years ago, but I didn't use the CXC transport with the ANK for very long.

In my experience that is not normal, though I have heard of that happening, but in using any number of different CD and DVD players as transports over the years, they've always locked for me straight off, so reliably that I had at one time wondered why there was even any real need for a lock LED indicator on the DAC.

One difference with my set-ups is that I've generally just left the DAC on at all times, only shutting off the transport when not in use, the exception being any DAC with vacuum tube output would be switched off to preserve tube life.

I wonder if this lock issue has something to do with that AN transformer?
 
In my experience that is not normal, though I have heard of that happening, but in using any number of different CD and DVD players as transports over the years, they've always locked for me straight off, so reliably that I had at one time wondered why there was even any real need for a lock LED indicator on the DAC.

One difference with my set-ups is that I've generally just left the DAC on at all times, only shutting off the transport when not in use, the exception being any DAC with vacuum tube output would be switched off to preserve tube life.

I wonder if this lock issue has something to do with that AN transformer?

Thanks for the reply. I vaguely recalled reading about “locking” issues in reviews of DACs many years ago but I couldn’t recall any details.

I don’t think the AN input transformer is the culprit since the problem occurred once before I installed the transformer, and once afterwards. As long as I can get things working again by turning the power off and then on again, it’s not a big deal. But it is odd.
 
In my experience that is not normal . . .
I agree that this isn't normal. Typically, the locking behavior is associated with the filter components for the clock and data recovery circuits in the CS8414. On the attached circuit diagram, they are the components going from FILT (pin 20) to AGND (pin 21). Over the years, there's been some discussion on the best way to optimize sound for the CS8412 and the CS8414. A fellow going by the moniker "wildmonkeysects" came up with the filter components which seem to be accepted as best for the CS8412. That should also work pretty well for the CS8414.
Relevant to your situation, wildmonkeysects noted that the chips (8412 or 8414) are quite sensitive to noise at the FILT pin and thus the filter component layout should be very short and compact. In the DACs that I've built using 8412 or 8414 receivers, I've used surface mount parts bridged between the FILT and AGND pins and never had any locking issues.
The layout on your DAC seems to use very long traces, so to improve the sound and to reduce the locking issue, I'd try adding the extra 3300pf that wildsects recommends directly between pins 20 and 21 of your CS8414. At some point you could also play with the RC combo attached to Pin 20 (470 ohms + 0.068uf in the diagram) but I'd first just try the extra capacitor.

CS8414.JPG
 

MikeyFresh

Moderator
Staff member
I'd also wonder if the turn-on sequence could be contributing to this issue. Try reversing the order of operations, turn on the DAC first, give it a second or two, then power on the transport and see if that is more reliable in terms of establishing lock.
 
I agree that this isn't normal. Typically, the locking behavior is associated with the filter components for the clock and data recovery circuits in the CS8414. On the attached circuit diagram, they are the components going from FILT (pin 20) to AGND (pin 21). Over the years, there's been some discussion on the best way to optimize sound for the CS8412 and the CS8414. A fellow going by the moniker "wildmonkeysects" came up with the filter components which seem to be accepted as best for the CS8412. That should also work pretty well for the CS8414.
Relevant to your situation, wildmonkeysects noted that the chips (8412 or 8414) are quite sensitive to noise at the FILT pin and thus the filter component layout should be very short and compact. In the DACs that I've built using 8412 or 8414 receivers, I've used surface mount parts bridged between the FILT and AGND pins and never had any locking issues.
The layout on your DAC seems to use very long traces, so to improve the sound and to reduce the locking issue, I'd try adding the extra 3300pf that wildsects recommends directly between pins 20 and 21 of your CS8414. At some point you could also play with the RC combo attached to Pin 20 (470 ohms + 0.068uf in the diagram) but I'd first just try the extra capacitor.

View attachment 18658

Thank you for the tip. Much appreciated. If the problem persists, I will try the 3300of.

I will also try reversing the power on sequence to see if that has any effect.
 
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