[steinba]

I'm thinking about building a DAC to use between my PPAv2/STEPS and computer or CD player. Hence I need both S/PDIF and USB inputs. (I guess the spdif input needs to be RCA, or is toslink also an alternative for a DIY DAC?)

Would anyone care to give me a hint about which of the DAC projects on the forum would suit my needs best. The price and SQ would ideally be in the "PPA range".

Thanks a lot in advance.

 

[Garbz]

Any DAC that has an S/PDIF input (BNC is better then RCA, RCA on S/PDIF is one of the industry's biggest mistakes), can be converted to having a Toslink interface. All you need is an inductor, a capacitor, and a TORX part, but you wouldn't want to. Toslink is horrible in comparison to coax.

USB can be attached via Guzzler's USB-> S/PDIF converter. Someone else may be able to point out some complete DACs that wouldn't need guzzlers board though.

 

[steinba]

S/PDIF outputs with BNC connectors? I've never seen that on any source. Is that a usual way of doing it? Why is that better?

 

[steinchen]

Quote:

Originally Posted by steinba Hence I need both S/PDIF and USB inputs. ... Would anyone care to give me a hint about which of the DAC projects on the forum would suit my needs best.

http://www6.head-fi.org/forums/showthread.php?t=157955
quite some pages meanwhile, you may start at page 15 or so

 

[splaz]

Well it's not the 'usual' way as in it's not what most consumer stuff comes with.

Same way F connectors were rarely used on VCRs and TVs, belling lee was and is almost always used. I personally don't like F that much, seems like I'm always going to bend the inner conductor. That's irrelevant though it still is superior to belling lee.

Same goest for BNC. It's better than RCA but not usually used.

RCA is more commonly used on everything else and probably cheaper to implement so they use that rather than BNC which seems pretty rare to see.

I don't know exactly why, but likely BNC make better contact, whether it's to the cable itself or female to male connection I'm not sure. I did make up a cable of it though and it's pretty fiddly to do, so I'd assume it makes a pretty good connection to the cable and maybe someone here may be able to shed light as to whether the actual male to female contact is any good.

I personally just like the way they lock on, seems more secure to me than the friction fit of RCA that at times seems a little dodgy.

 

[DaKi][er]

Quote:

Originally Posted by splaz I don't know exactly why, but likely BNC make better contact, whether it's to the cable itself or female to male connection I'm not sure. I did make up a cable of it though and it's pretty fiddly to do, so I'd assume it makes a pretty good connection to the cable and maybe someone here may be able to shed light as to whether the actual male to female contact is any good.

The reason it is preferred is that it maintains a consistent impedance from the source to the destination, 75ohm is the spec for digital audio and rca's are not 75ohm (usually measure about 25-30)

That issue aside, there are plenty of more important issues in building a dac that for the beginner i wouldn't really recommend it, especially if you aren't going to put in the hard effort of researching it all

 

[splaz]

Well impedance it is.

So the cable I made up is 50 ohm, for test equipment, would that work just as well as an RCA or better for digital audio then ?

I know ideally you'd have the 75 ohm but just out of curiosity.

Sorry to get a bit OT by the way.

 

[Reighlok]

Quote:

Originally Posted by Garbz Any DAC that has an S/PDIF input (BNC is better then RCA, RCA on S/PDIF is one of the industry's biggest mistakes), can be converted to having a Toslink interface. All you need is an inductor, a capacitor, and a TORX part, but you wouldn't want to. Toslink is horrible in comparison to coax. USB can be attached via Guzzler's USB-> S/PDIF converter. Someone else may be able to point out some complete DACs that wouldn't need guzzlers board though.

Since the group buy for guzzler's boards is over, does that mean that the converter can be made without the pcb?

EDIT:
The same is true of the linked DAC.

 

[randytsuch]

Quote:

Originally Posted by splaz Well impedance it is. So the cable I made up is 50 ohm, for test equipment, would that work just as well as an RCA or better for digital audio then ? I know ideally you'd have the 75 ohm but just out of curiosity. Sorry to get a bit OT by the way.

Might be better than RCA, but it is still not ideal.
If you have any impedance other than 75 ohms, you will get signal reflections. The more mismatches you have, or the great the mismatch, the larger the reflection. These reflections degrade the signal.
So, in a perfect world, the signal path is 75 ohm from beginning to end, but nothing is perfect, so there will be some reflections, you just want to minimize them.

People make 75 ohm RCA's, but the problem is, you need 75 ohm RCA for both the plug and the jack, or it is not really 75 ohms. You can get 75 ohm BNC's, and then you are set.

Randy

 

[Pars]

None of the so-called 75-ohm RCAs are really 75 ohms, and even if they were, you would still need to use a "75-ohm" jack on your equipment as well. Probably closer to 30. For best performance, replace all digital connectors with 75 ohm BNCs and use 75 ohm coax. Including the source (transport, CD digital out) and the DAC.

Makes me think about those component video cables with the Canare RCAs... hmmm, might have to tear into the Sony

.