Some CD and DVD players stop producing a digital signal when there is no disc in the drawer or "stop" is hit. This "unlocks" the DAC, resulting in noise. When a disc is inserted, the transport starts sending out a digital signal, causing the DAC to respond and lock onto the signal. The "locking" and "unlocking" is what may be causing the noise that you hear. This noise could be potentially dangerous to your tweeters, so you may want to think about discontinuing the use of your DAC and / or getting another transport. This is just a guess though, so keep that in mind. Sean
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I also have a Museatex DAC and have the same experience, albiet mine happens more occasionally. I asked John Wright about the noise and he explained that the initial click you hear when the "CLock" indicator illuminates is caused by the DAC recognizing the signal and opening the output relay. In turn, the "crackle" that you sometimes hear from the speaker is the result of a tiny residual DC voltage that can be present until the servo catches up and nulls it out. This is normal and rather low in level, so it shouldn't pose a threat to your tweeters. However, if you're worried about it then just turn down the volume or hit the mute button when cueing up a disc. |
I always get a quick, loud and sharp crackle...its bad and very loud. I've tried everything, I have noticed that it only happens after closing the CD drawer and the cd begins to load, the speakers burst out in crackle. I have avoided this problem by switching the Museatex to optic settings, then switching back to Wire (coxial) when the disc has loaded and playing, everything seems fine.
Surely there has to be a better way so I can get rid of this very unpleasent distortion and not have to worry about switchin my DAC settings everytime I change a disc. |
pbawcutt,
Do you mean that the crackle doesn't happen when the DAC's optical digital input is used ("I have avoided this problem by switching the Museatex to optic settings, then switching back to Wire")? This sounds odd, because the phenomenon that I described is totally independent of what digital input is used. Like I said, a small crackle sound is normal, but in my experience it isn't as bad as what you're describing. Perhaps your amp's input sensitivity and/or your speakers' sensitivity is higher than mine, which is exacerbating the issue. However, I doubt this is the case given that there are many Museatex DACs in the field, and I've never heard of a "normal" unit behaving like this. I'd suggest three things:
1. Try using the DAC with a friend's CD player/transport, and see if the same problem occurs. This would at least rule out that it's related to the NAD's coax output.
2. It may turn out that your unit has a problem, like a bad servo circuit that's failing to null the DC properly. It's therefore a good idea to send John Wright an email. You'll find his contact info at www.museatex.com, and I've found him to be great to work with.
3. A properly functioning unit is going to exhibit the occasional mild crackle when the CLock engages. It's simply the nature of the beast. In the end, if it turns out there's nothing "broken" with the DAC but you just can't live with this issue, and turning down the volume when you change the disc is not a satisfactory solution, then perhaps this relationship wasn't meant to be.
Best of luck. |
Hey Oxia, I have my amp's volume set to 0 and it still happens. What i meant by switchin to Optic was, I only change the setting, there isn't really a wire hooked up there, but when I change to optic setting, allow the disc to load, then press play on the NAD, I switch back the DAC to wire setting, and no cracks or distortion.
It's very strange indeed. |
Hmmm. So to summarize, these are the two scenarios:
A)
-The DAC is configured to use the coaxial digital input
-You then put in a CD
-The CD player reads the TOC and outputs a signal
-The DAC recognizes the signal; CLock engages
-You get a sharp "crackle" from your speaker
B)
-The DAC is configured to use the optical digital input
-You then put in a CD
-The CD player reads the TOC and outputs a signal (the DAC doesn't receive the signal because it's not hooked up via the Toslink connection)
-You switch the DAC to the coaxial input
-The DAC recognizes the signal; CLock engages
-You get no "crackle"
It sounds strange because I would think that since the ouput relay and servo are engaged when the DAC receives the signal, then if they are the cause of the problem (i.e. they are faulty) it shouldn't make a difference whether you use method "A" or "B". One possibility is that there is a brief initial "burst" discharge from the NAD's digital output when it sends a signal, which goes away after it has a second or two to settle. Perhaps this is upsetting the DAC's receiver, and by switching the DAC's input off and then on a bit later, you are effectively giving the transport's digital output enough time to settle before engaging the DAC. Have you tried using the DAC with another transport? Have you used different DACs with the NAD? Again, I would encourage you to email John Wright for his thoughts.
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It was the NAD, I've since used another Transport and I didn't get the problem.
I have no idea why this happens with the NAD. I can avoid the problem by switching it to optical and then back to coax once it's loaded.
Im not sure I could buy a DAC that would beat the NAD handsdown for under $500 as a simple transport, so I might keep the NAD for awhile, I've seen a Theta and CAL audio Lab transports for sub $500 but I have no way of telling if they would be a sonic improvement to the NAD, so I might just live with it for awhile. |
The NAD doesn't send a continuous digital signal all the time. As such, what you are hearing is the DAC locking and unlocking. This is what i described in my first response. This is a common problem with some specific CD and / or DVD players when used as transports. Before buying something else, you should contact the manufacturer to find out if the transport constantly sends a signal out of the coaxial jack or if it engages as needed. Sean
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Hey Sean, thx. Do you know of any used CDP's that I could buy and use as a dedicated Transport, which would have a digital signal sent out at all times? Ideally I'd like to sell my NAD 541i and use that money to buy an equally as good transport. Perhaps an older ROTEL, ARCAM, or something? The idea of a detachable power cord for future upgrades would be also nice. |
This is a more common problem with newer CD players and most DVD players. From what i can recall, there's "probably" a very simple modification that can be done to your DAC to correct this problem. I had to perform a similar mod to some 24 bit CAL dac's that i had several years ago due to the same problem. Whether or not you want to send your DAC in to do something like this is another matter.
As far as selecting a good transport that will negate this problem, i don't know what to suggest to you. You might want to look through the archives to see what has been suggested as being a cost effective transport. Once you narrow your search down, i would suggest calling the manufacturer to find out if that specific model outputs a constant signal or makes / breaks as needed. Given that your specific DAC "probably" ( i think that it does ) re-clocks the incoming signal that is sent to it, it might not be as sensitive to transports as some other less well designed DAC's. That's because the higher than average jitter that a lower grade transport produces is no longer a factor. That doesn't mean that "anything" will work optimally as a transport, only that you might have more options open to you. Sean
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