Cable recommendation for long distance between PC and DAC

[northpaw]

Good progress so far, but I don't see how you eliminated the possibility of the DAC simply being bad. It did not work with USB on the first PC, doesn't work with USB on a second PC (casting doubt on the soundcard theory, as both soundcards would have to be bad), and now it does not work with optical input. That makes it even less likely to be just a USB problem. If you are concerned about your optical cable, a cheap check on it is to carefully look at the "DAC" end of the optical cable (a bit sideways) while sound is playing on the TV and look for blinking red light (don't look directly at it, of course, it is a laser). Edit: better yet, just point the DAC end of the optical cable to a while index card or the like, an inch away; that should allow you to see the red light.

It seems to me that the DAC is the likely problem, and if so may not be worth trying to fix. There are some very attractive DAC options out there now, so you have alternative pathways if the CA DAC is dead and you are keen on trying one out.

 

[gvl]

It seems to me that the DAC is the likely problem, and if so may not be worth trying to fix.

+1. The fact that the DAC recognizes changes in sampling rates is a good indicator that the digital link is working but something is wrong down the line, like the analog stage power supply isn't working. Perhaps open it up and see if there are obvious signs of problems like burnt components or maybe even missing parts?

 

[cloneofkane]

Good progress so far, but I don't see how you eliminated the possibility of the DAC simply being bad. It did not work with USB on the first PC, doesn't work with USB on a second PC (casting doubt on the soundcard theory, as both soundcards would have to be bad), and now it does not work with optical input. That makes it even less likely to be just a USB problem. If you are concerned about your optical cable, a cheap check on it is to carefully look at the "DAC" end of the optical cable (a bit sideways) while sound is playing on the TV and look for blinking red light (don't look directly at it, of course, it is a laser). Edit: better yet, just point the DAC end of the optical cable to a while index card or the like, an inch away; that should allow you to see the red light.

It seems to me that the DAC is the likely problem, and if so may not be worth trying to fix. There are some very attractive DAC options out there now, so you have alternative pathways if the CA DAC is dead and you are keen on trying one out.

I checked out the toslink/optical cable hooked up to both my PC and the TV (same settings as above) with sound playing and there is a solid red light, not a blinking light. Does that mean my toslink cable is bad?

 

[cloneofkane]

+1. The fact that the DAC recognizes changes in sampling rates is a good indicator that the digital link is working but something is wrong down the line, like the analog stage power supply isn't working. Perhaps open it up and see if there are obvious signs of problems like burnt components or maybe even missing parts?

Sounds like the right next step.

 

[gvl]

I checked out the toslink/optical cable hooked up to both my PC and the TV (same settings as above) with sound playing and there is a solid red light, not a blinking light. Does that mean my toslink cable is bad?

It is blinking at 100000 times per second, movies are 24 frames per second. Human eye is a very imprecise optical device.

 

[northpaw]

yeah, what gvl said. wasn't thinking, and couldn't remember the rare times I have done this if I saw blinking or just solid red.

 

[cloneofkane]

I removed the rear panel to find out that the top and bottom panel are secured to the inside of the front panel, requiring a long-ass phillips head about 8" from handle to tip to reach the screws. I can't see the caps up at the very front of the board, and everything else looks very clean except for one large cap that appears to have crud/corrosion at its base (see attachment). I can buy the screw driver and replace that capacitor, but it would be awesome to determine if that could be the issue before investing the time and $ into replacing it. I will send this to the Cambridge Audio folks to see if they can tell me anything about that particular cap.

 

[northpaw]

That cap base does look dodgy, but I suppose you would have to get at it to evaluate. Do you know the value of the cap? There is an owners manual and service manual for this over at hifiengine (I have not looked at them, but I see they are there), and they may allow you to ID it. If it is a power supply cap (these are usually the biggest on the board), you can use the same approach we discussed back when it was the NAD that had the power supply cap problem, if you can access its leads. If it is not a power supply cap, not so easy to check/evaluate in situ (at least not that I know, and my knowledge is limited).

More generally, I think what gvl was indicating about checking the analog power supply was to use the schematic and layout diagrams to find places you can measure the +/- supply voltages (DC), and see if they agree with the voltages shown on the schematics. This DAC may have separate digital and analog power supplies, so be sure to be cognizant of that while looking. The checking of AC ripple across the power supply caps, as we discussed in that other thread, is somewhat different kind of check, being a way to see if those caps are doing their job of filtering the AC.

 

[cloneofkane]

That cap base does look dodgy, but I suppose you would have to get at it to evaluate. Do you know the value of the cap? There is an owners manual and service manual for this over at hifiengine (I have not looked at them, but I see they are there), and they may allow you to ID it. If it is a power supply cap (these are usually the biggest on the board), you can use the same approach we discussed back when it was the NAD that had the power supply cap problem, if you can access its leads. If it is not a power supply cap, not so easy to check/evaluate in situ (at least not that I know, and my knowledge is limited).

More generally, I think what gvl was indicating about checking the analog power supply was to use the schematic and layout diagrams to find places you can measure the +/- supply voltages (DC), and see if they agree with the voltages shown on the schematics. This DAC may have separate digital and analog power supplies, so be sure to be cognizant of that while looking. The checking of AC ripple across the power supply caps, as we discussed in that other thread, is somewhat different kind of check, being a way to see if those caps are doing their job of filtering the AC.

I haven't been able to get into it more than the pictures I took from the outside. I need to get one of those long screwdrivers and get the darn thing apart first. Honestly, I think I will wait to do anything until I hear back from Cambridge Audio tech support. They may have something to try before going the recap route. If not, maybe they can provide a parts list.

Couple of interesting notes:

1) Here is a link about this DAC my brother sent me -- very technical, but thorough look at the guts: http://rockgrotto.proboards.com/thread/6427/page/2/cambridge-audio-dacmagic
2) I was telling my brother that it is giving off a sickly sweet smell, even having been shut down for a while. He thought it might be the smell of cap venting.

And one more general question: if you were me, would you pursue repairing further or just try a $100-$200 new DAC?

Thanks for the advice and answers -- so many great folks on AK!

 

[northpaw]

Waiting to hear from CA sounds like a good plan. As to if it is worth trying to fix, you'll need the opinions of people who know more about DACs than I do.

The internals do look to be very well built, with many film caps, presumably in the signal path, a good sign. Most of the components are surface mount, meaning hobbyists like us will have a lot of difficulty in working with those components (not advised), but the larger electrolytic caps certainly can be worked on. I would look at it this way: its present value is presumably pretty low, given the age and its problems. If you are inclined to open it up and get a better sense of what might be wrong (hopefully just cap(s)), it can be an interesting project to take on at your leisure. As long as you can power up when you have it opened up, you can do some basic checking. Depending on what you find, you can sew it back up and sell as is for a nominal amount, or give it a go. Caps are not expensive, so as far as costs it might be just some caps and the long screwdriver, which will live on. I did look at the service manual, and there are no layout diagrams, making finding things more difficult, but not impossible, to work on, especially since the layout from the photos you linked do not look overly complicated.

The sweet smell I am not sure about; maybe someone else knows. I don't know what leaked electrolyte smells like, but I thought it would be alkaline/caustic. The two other possibilities that come to mind are excess flux on the boards slowly vaporizing (would be similar to the smell you get when soldering with rosin-core solder and/or extra flux, which you should know), and the smell that comes from phenolic plastics when they are heated. In my memory, this is associated with the back of operating TV sets in the late 1950s to 1960s, or burned up electrics near the transformer on Lionel toy trains. But this unit seems way too new for that; in fact, it looks like it has quality fiberglass PCBs.

Edit: Forgot to mention that the inclusion of the XLR connectors on the back panel are another indication of a unit aimed at the mid-fi or higher segment of the market.

 

[rwartner]

If it was me - I would screw it up worse. The question is whether to get a new DAC. You have a really nice system.
Consider what you would use the DAC for. What inputs and outputs are needed. You have the distance problem.
Is it worth it to spend the money?

Here is a simple wireless solution as example.
https://audioengineusa.com/shop/adapters/w3-wireless-audio-adapter/

I use the previous model and works fine. Maybe take a look at eBay to see if something cheaper.

 

[gvl]

And one more general question: if you were me, would you pursue repairing further or just try a $100-$200 new DAC?

I'm unable to provide a rational reason to invest any time and money in fixing an aging and while decent but otherwise unremarkable piece of equipment whose value is about $100-$150 on the used market today in working condition. The irrational reasons are there of course, so if you have the time, skills and interest doing it then why not?