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Word Clock Question for Opus

Discussion in 'Recording' started by phalic, Aug 3, 2003.

  1. phalic

    phalic Guest

    Opus,

    Im trying to figure out what needs to be terminated in my rig?My rig is as follows:

    Lucid genx 6(masterclock)Sending individual word clock signal on 75 ohm apogee cables to the following slaves:

    Apogee ad16
    Frontier tango24 ada
    rme hammerfall
    My question is do each one of my slaves need to be terminated?If so how?Rme<s manual states if the hammerfall is last in a series set up,witch mine is not,to use a t with a terminator.Or should i just terminate the wc outputs on the apogee, the tango, and the rme?

    very confused

    thanks

    p
     
  2. Opus2000

    Opus2000 Well-Known Member

    Basically you should make sure that all devices are terminated. Wiithout termination you could possibly cause some reflections within the word clock circuitry and cables.

    Think of it this way, analog TV days when you saw a slight ghosting in the screen...that sort of off double vision type stuff..thats basically what can happen with non terminated devices.

    The best thing to do is to get yourself a BNC T connector and attach it to every word clock input and terminate it with a 75 Ohm termintaor cap.

    Hope that helps..or for James..HTH! lol

    Opus :D
     
  3. phalic

    phalic Guest

    thanks opus will do.
     
  4. Doublehelix

    Doublehelix Well-Known Member

    Actually, you should have said:

    "HTH or for James...Hope that helps!"

    lol!

    YNIACFIWICTA (You know I am a complete freakin' idiot when it comes to acronyms!)
     
  5. falkon2

    falkon2 Well-Known Member

  6. realdynamix

    realdynamix Well-Known Member

    :) Hi Opus, I know what you mean by termination. Termination will remain 75ohm, if it is a loop through with a single termination. If a tee is used, it is not like a normal split, it becomes double termination. Actually one end would have to remain open to be remain 75ohm. A distribution system, or loop through with a final 75 ohm terminator, would be the better recommendation. Is this possible with the gear you are talking about?

    --Rick
     
  7. Doublehelix

    Doublehelix Well-Known Member

    I have not terminated anything in my clocking scheme. I have 4 devices clocked from my Lucid clock (sorry Opus!), and they are all connected directly from the clock to the WC input on each device. So should I invest in a few T-connectors and 75 ohm terminators, or only if I am experiencing problems?

    Thanks!
     
  8. realdynamix

    realdynamix Well-Known Member

    :) To help clarify. The devices may have built in distribution or (direct coupled inputs), this is no problem looping device to device. If the devices have a dual set of 75 ohm connectors. It can be connected one to the other, to the other etc., then finally terminated. If they are loop through connections, a terminator may be required, or the device may be self terminating. When you use a Tee connector, because of the split, you can't single end terminate, you can cap it(shield only). But if you terminate you will reduce amplitude nearly by half. Hard to detect, since digital is still recognizable at low levels. Better to have full amplitude.

    --Rick
     
  9. realdynamix

    realdynamix Well-Known Member

    :) DH, does your clock provide four or more outs? If it does then this is distribution.

    --Rick
     
  10. Opus2000

    Opus2000 Well-Known Member

    Rick Rick Rick....tsk tsk tsk...

    It is NEVER recommended to go in and out of a device with word clock! This is daisy chaining and with that you could cause a slight lag in the word clock at that point! This would lead to bad clocking and possible drift in clock or pops and clicks! BAD...VERY BAD! :D

    Direct loop though ports are rare on devices and most have an in and an out! Each time you go in and then to the out you have a slight propogation delay!

    Now, to tell and Apogee tech that a BNC T connector is a double termination is quite bold my friend! :D
     
  11. realdynamix

    realdynamix Well-Known Member

     
  12. Opus2000

    Opus2000 Well-Known Member

    Yes, double termination would be bad but indeed that is dependant on the device in question!

    If the device in question is auto terminated, which I believe in the long run it should not be, as to allow the flexability of the users choice!

    In fact terminating on a BNC T connector is the best way as it is terminated at the point of reference and not after the fact!

    Indeed, scopes are a plenty here at work! lol

    Yes, Big Ben is a must have! Spread the word my friend! As well as the love! lol

    Opus :D
     
  13. phalic

    phalic Guest

    Opus
    one more quick question,I know bnc terminators come in different ohm values,but is there a 75 ohm T adapter?If so,know of any good online stores to get um from?

    thanks

    p
     
  14. Opus2000

    Opus2000 Well-Known Member

    http://www.pacrad.com/index.shtml

    They always have that sort of stuff!

    Their online store seems to be having some difficulties at the moment so keep checking on it!

    Opus :D
     
  15. Doublehelix

    Doublehelix Well-Known Member

    I have the Lucid Genx6-96, which has 6 bnc word clock outs. Four of these are connected directly to the word clock ins on four separate devices with four digital bnc cables. The remaining 2 outs on the Lucid clock are not terminated, in fact I have no t-connectors or terminators in the entire chain.

    Based on that info, are there any modifications to my setup that are required?

    Thanks!
     
  16. Opus2000

    Opus2000 Well-Known Member

    DH

    The outputs of the distribution box do not need to be terminated. It's only in reference to actual devices that have input and output word clock connections to them.

    Depending on the gear and whether it is self terminating will determine whether or not you need to get a termination cap for it or not.

    It would be a good idea to get some BNC T connectors and some 75 Ohm terminator caps to make sure that they are indeed terminated!

    Or you could just send Arnold in and have him terminate them :D
     
  17. Doublehelix

    Doublehelix Well-Known Member

    Thanks for your help Gary...I am almost there...

    So, the next question that begs to be asked is "How can I tell if a piece of gear is self-terminating?" Can I just hook up my multi-meter to the bnc and see if has 75 ohms of resistance?

    Is it going to hurt if I just go ahead and terminate all of the devices, just to be safe? In otherwords, add t connectors and 75 ohm terminator caps to the back of each device...

    Thanks again!
     
  18. knightfly

    knightfly Active Member

    James, don't do that. Rick is right about levels and terminations, you ONLY want ONE termination resistor per WC output, and that resistor needs to be ONLY at the END of that particular transmission line. You should (unless they've done something really wierd) be able to measure the DC resistance at the BNC, and see 75 ohms to ground if it's terminated internally. Not sure about various digital audio gear, but Video gear lots of times will have a switch next to the connector(s) that's labeled - usually with two connectors. If you're looping thru, you set the switch to "off".

    You have your system WIRED correctly, with one output going to one device through one cable. You would need to either measure, RTFM, or both, for each piece of gear to find out about termination. What you should end up with, is one 75 ohm load at the very END of each path.

    I'm more used to VIDEO gear as far as terminations are concerned, so I can't say (without a manual) whether it's all that common for audio gear to have a termination SWITCH. With all the tech improvements that have taken place in the last decade or so, I wouldn't be surprised if some gear has the ability to sense whether you've connected another cable and "daisy-chained" two or more units together. I would definitely agree with Gary on this though - DON'T. I could see maybe a second piece of gear if you're out of discreet outputs from the GenX, but you're not.

    And, technically, STANDARD BNC connectors are actually rated as 50 ohm impedance. They sell SPECIFIC parts that are rated for 75 ohm impedance. I get a little confused by that crap myself. For example: RG-59, which is 75 ohm cable, is thicker than RG-58, which is 50 ohm cable. Does this mean that BNC connectors for RG-59 are automatically 75 ohm? apparently not, because Newark lists BOTH types for RG-59, as do other catalogs. Same with adapters, such as Tees, 90's, and such.

    I've yet to actually SEE any difference in video that was run with 50-ohm CONNECTORS, as long as the CABLE was correct - However, anything that could cause timing errors between pieces of digital audio gear I would automatically AVOID, including a possible waveform glitch caused by a miniscule impedance mismatch (such as a 50-ohm connector or tee on a 75 ohm line)

    Bottom line is, if you're going to go to the expense of a proper clock gen/DA, you should FINISH the job with proper cabling and termination. This would include making ALL the cables from the clock gen/DA the same length, even if you have to coil the extra somewhere. The length should be just long enough to reach the furthest away piece of gear. Why settle for anything less than BEST, when it's just a matter of small details?

    OK, the crazies have now been represented... Steve
     
  19. phalic

    phalic Guest

    Why same Length cables?
     

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