Pre-DAC switching capability?

Discussion in 'DIY Discussion' started by Commited, Jan 3, 2006.

  1. Commited

    Commited

    Joined:
    Jan 30, 2005
    Messages:
    34
    Likes Received:
    0
    Hi all,

    Long time since I've posted, but after such a great experience with the t-amp, the DIY upgrade bug has bitten again!

    I've decided to buy the Monica 2 DAC from DIY Paradise to mate to my Arcam 7SE. From listening to my fathers Derek Shek NOS Dac v2, I can tell that it's going to be a good upgrade, and hopefully should be even better than the NOS Dac from what I read.

    As I listen to a combination of mp3s and CDs, I would like to use this DAC with both computer and CD sources. As the computer is an optical SPDIF output, I'll be using a converter: http://www.audioshowcase.com/popupspecs/10tr-08300.htm . Are there any known problems with this converter? Will it mess with the sound much?

    Rather than continually change sources, I was wondering if there was any such thing as a Co-axial switch, or if there are simple schematics so that I could build one myself (easier the better!). Ideally I'd like to have the switch in the box with the DAC.

    So - is this a crazy idea or might it work?

    Cheers
    Mark

    P.S - I hear that the Monica 2 lowers the CDP output level a bit - will this be an issue with the t-amp, as it isnt exactly the loudest amp in the world!
     
    Last edited by a moderator: Jan 3, 2006
    Commited, Jan 3, 2006
    #1
  2. Commited

    Tenson Moderator

    Joined:
    Nov 12, 2003
    Messages:
    5,947
    Likes Received:
    1
    Location:
    Kent, UK
    I see no reason why you can't just use a normal switch to change the co-axial inputs.
     
    Tenson, Jan 3, 2006
    #2
  3. Commited

    Commited

    Joined:
    Jan 30, 2005
    Messages:
    34
    Likes Received:
    0
    really? If it is that simple It'll be great!
     
    Commited, Jan 3, 2006
    #3
  4. Commited

    zanash

    Joined:
    Jun 20, 2003
    Messages:
    3,826
    Likes Received:
    2
    Location:
    Notts.
    Remember there are things you can do to the 7se to help it on its way. If your intrested I can ferret out some schematics and a few pointers.
     
    zanash, Jan 10, 2006
    #4
  5. Commited

    Andrew L Weekes

    Joined:
    Dec 2, 2003
    Messages:
    78
    Likes Received:
    0
    Location:
    Sevenoaks, Kent
    A normal switch would create a significant mismatch which would degrade performance. You'd really need to use a coaxial 75R relay, not a common thing to find!.

    You could also do it with PIN diodes, but that requires more work and some knowledge of how to match RF networks.

    I have a similar Optical converter and it certainly wasn't ther best quality device in the world, but for PC use and mp3's it would probably be fine, given that optical connections are of lower quality than a good electrical one.

    All in all, I really can't recommend the switching idea.

    Andy.
     
    Andrew L Weekes, Jan 10, 2006
    #5
  6. Commited

    Commited

    Joined:
    Jan 30, 2005
    Messages:
    34
    Likes Received:
    0
    Zanash,
    Thanks! I have sent you an email.

    Andrew,
    Thanks for the reply!
    I have found this: http://www.revealcable.co.uk/acatalog/info_AA_2362.html
    It seems like what I'm looking for, I just dont want to be swapping out cables all the time. Would that switch box degrade the sound much in your opinion?
    In the future I will splash out on a dedicated DAC for the PC, but money is tight at the moment!

    Thanks,
    Mark
     
    Commited, Jan 11, 2006
    #6
  7. Commited

    Tenson Moderator

    Joined:
    Nov 12, 2003
    Messages:
    5,947
    Likes Received:
    1
    Location:
    Kent, UK
    Any clues?
     
    Tenson, Jan 11, 2006
    #7
  8. Commited

    SteveC PrimaLuna is not cheese

    Joined:
    Aug 31, 2003
    Messages:
    854
    Likes Received:
    0
    Location:
    SE Norway
    SteveC, Jan 11, 2006
    #8
  9. Commited

    zanash

    Joined:
    Jun 20, 2003
    Messages:
    3,826
    Likes Received:
    2
    Location:
    Notts.
    Did you ....? Did I respond can't find it in my inbox ?
     
    zanash, Jan 11, 2006
    #9
  10. Commited

    Andrew L Weekes

    Joined:
    Dec 2, 2003
    Messages:
    78
    Likes Received:
    0
    Location:
    Sevenoaks, Kent
    10BASE-T networks are unfortunately 50R, not 75R. I'd also have my doubts that it's of very high quality (in terms of maintaining constant Z throughout, since it's far less critical for a PC network. Depends on how good your system is already - if it uses a phono for SPDIF, it's not 75R anyway since there's no such thing as a 75R RCA phono, so it probably doesn't matter!

    CCR33M from http://www.teledynerelays.com/electroprod.asp looks like the ticket, if you can get some 75R SMB connectors (didn't even know they existed!) to mate with it.

    BNC would be easier though - any RF-rated, 75R coaxial relay should be more than adequate, the only possible thing you may need to watch is the current / power the switching contacts are designed for. With some too low a current (like an SPDIF application) means the surface oxides on the terminals build up, giving rise to long-term unreliability. For 75R stuff you probably need to look to video or broadcast suppliers, since it's common there.

    Andy.
     
    Andrew L Weekes, Jan 12, 2006
    #10
  11. Commited

    Tenson Moderator

    Joined:
    Nov 12, 2003
    Messages:
    5,947
    Likes Received:
    1
    Location:
    Kent, UK
    Just why do people use RCA for coax digital? I never understood that!
     
    Tenson, Jan 12, 2006
    #11
  12. Commited

    Commited

    Joined:
    Jan 30, 2005
    Messages:
    34
    Likes Received:
    0
    Commited, Jan 13, 2006
    #12
  13. Commited

    Andrew L Weekes

    Joined:
    Dec 2, 2003
    Messages:
    78
    Likes Received:
    0
    Location:
    Sevenoaks, Kent
    For commercial equipment it's defined within the Sony / Philips Digital Interface Format as having an RCA phono.

    I guess the talented engineers at Sony and Philips thought it wouldn't matter - but it does!

    The outcome is that any commecial equipment using anything other than a Phono is not strictly compliant with the specification.

    Andy.
     
    Andrew L Weekes, Jan 13, 2006
    #13
  14. Commited

    Commited

    Joined:
    Jan 30, 2005
    Messages:
    34
    Likes Received:
    0
    Any ideas on the ebay link above?
     
    Commited, Jan 13, 2006
    #14
  15. Commited

    Commited

    Joined:
    Jan 30, 2005
    Messages:
    34
    Likes Received:
    0
    Commited, Jan 19, 2006
    #15
  16. Commited

    I-S Good Evening.... Infidel

    Joined:
    Jun 25, 2003
    Messages:
    4,842
    Likes Received:
    1
    Location:
    In a world of pain
    You've got me thinking here....

    The CS8414 DIR used in the monica 2 will tolerate up to +/- 12V (abs max) on its digital input.

    This means that there's no issue in taking multiple SPDIF inputs, converting them up to 5V (or 3.3V...) TTL logic level, and MUXing them into the CS8414. There's a certain 3-input (optical, spdif, AES/EBU) DAC on the market which does exactly this.
     
    I-S, Jan 19, 2006
    #16
Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.