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SPDIF amplifier

Discussion in 'Electronic Design' started by Dirk Bruere at NeoPax, Mar 1, 2007.

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  1. I want to amplify and distribute SPDIF to three systems over maybe
    100m feeding into systems that take AES/EBU.
    So, thinking of putting the SPDIF through an amp and then splitting it
    through a 4 Way off the shelf passive F- Splitter.
    Can anyone recommend a cheap amp that might be suitable for this?
    People have suggested TV amps but I can't seem to find any that don't
    cut off below about 88MHz (FM).

    I'd also like to boost the voltage a bit as well since I'm feeding
    into EAS/EBU.
    I know I could probably put one together using a buffer amp chip or
    something but I don't want to have to get into making, soldering and
    packaging a solution of my own.

    Someone somewhere must do what I want at a reasonable price.
    I know someone does it at an *unreasonable* price - approx $350, but
    that seems aimed at audiofools.

  2. Hawker

    Hawker Guest

    Why don't you buy or build a COP and convert it to AES then send it.
    AES is designed to send on long runs, SPDIF is not. Since your going to
    AES in the end just convert to AES at the source and use balanced CAT-5
    cable to get it to the XLRs on the AES.

  3. "COP"?
    Anyway, building is out of the question for various reasons.
    Still, your advice sounds good.

  4. Another quick question.
    If/when I get my AES signal how do I split it?
    Can I just join the cables at source or do I need do do anything with
    resistors etc to match impedances etc?

  5. Mark Zenier

    Mark Zenier Guest

    What about a distribution amp for VGA video?

    Mark Zenier
    Googleproofaddress(account:mzenier provider:eskimo domain:com)
  6. Genome

    Genome Guest

  7. Hawker

    Hawker Guest

    In response to your COP question and splitting.
    A COP was a device made by Fostex (COP-1) that was designed to do this.
    I don't know if they are still made or not but COP has become a
    generic word these days to refer to a device for SPDIF to AES conversion.
    Check with Full compass or some other company for what they have. I
    think - Gasp - Beheringer and others make such devices on the cheap.

    As for splitting.
    AES-1992 (what I assume you are referring to as opposed to the AES over
    Coax who's name escapes me right now) is basically RS-422. RS-422 cannot
    be "split" it must be daisy chained so you go from the source to the
    first input and out from it (directly at the XLR connector) to the last
    one. You terminate the last input.
    The problem with this is most manufactures terminate all AES inputs so
    if you split it you get double termination. It "Might" work but it is
    not a good idea. You can remove one terminator, or you can try an active
    splitter. An active splitter will consist of 1 receiver and 2
    transmitters. Or you can go into the first AES in, out the AES out and
    into the AES in of the second device. Simple splitting as you imply is
    not going to cut it.

    Good luck
  8. Guest

    You may be able to run SPDIF through a distribution amp designed for
    BASEBAND video, however the signal levels for SPDIF tend to be higher
    (or was it lower?) so that may not work too well.

    But the first thing to realize about SPDIF is that it is a digital
    signal, so you don't need the kind of linear amplifier intended for
    video... in fact, you would do much better with a non-linear amplier
    such as a logic gate. The idea is to make a decision about the
    incomming signal, and then loudly proclaim the answer, renewing your
    noise margins.

    With some care at the input circuits and a 75 ohm series resistor on
    the output you could probably use any 74xxx series CMOS.... I think
    you can even invert the signal with no problem. In actual products,
    I've seen RS422 driver chips used. One thing you do want to be
    careful of though is that you get something that does not distort the
    duty cycle of the waveform - some receivers have trouble locking to
    the embedded clock if the duty cycle is far off.

    And in playing with SPDIF a a scope is an essential tool. Always make
    sure to terminte your inputs in the characteristic impedance of the
    line... otherwise you will get ringing, and that will case failures...
    I've hardly ever seen a more practical example of transmission line
    effects - literally had setups that did not work, stuck a short Y
    cable at the receiver, popped a terminating resistor on the extra
    lead, it works, take the resistor off it doesn't... that was of
    course an input with the design flaw of presenting an impedance much,
    much higher than 75 ohms.
  9. The three machines that need the AES signal are in different locations.

    Dirk - The UK's only occult talk show
    Presented by Dirk Bruere and Marc Power on ResonanceFM 104.4
  10. Eeyore

    Eeyore Guest

    A video DA should be OK to distribute SPDIF but the signal voltage of SPDIF is
    too low for AES.

  11. I know, although it's right on the edge over short runs.
    I was hoping for a bit of voltage amplification.
    Anyway, look like I'm going to have to make my own given the ludicrous
    prices companies are charging for what is basically a simple circuit.
    I estimate that the total cost of the parts excluding PCB for a 1:3
    distributor will be around £10 one off. And that includes xformer

    Which is somewhat lower than the hundreds I've seen quoted.
    Just got to find a decent circuit design, or create one.
    Been looking at this (half way down)

    Opinions? Suggestions?

    Maybe I'll sell some as a sideline...

  12. Eeyore

    Eeyore Guest

    Ebay of course !

  13. Looks like I'm going to be doing a DIY job, since we can't buy in at the
    right price.

    So, here's the design.

    SPDIF feeding into an AD818 wideband amp, with a gain of 4.
    The o/p of this to an HC Schitt trigger and this feeds into four RS485
    line drivers. Each o/p then drives an audio digital transformer for
    isolation (and to get rid of any potential ground loop problems we may


    Dirk - The UK's only occult talk show
    Presented by Dirk Bruere and Marc Power on ResonanceFM 104.4
  14. BTW, I'll be using the free Eagle layout package and a cheap PCB
    prototyping house in the UK. Apart from my valuable time I estimate
    total overall cost for a 1 in 4 out converter (one off initially) to be
    around $100 including XLR connectors.

    Production should bring that down to around $50 in the quantities we
    want including labour cost.

    Dirk - The UK's only occult talk show
    Presented by Dirk Bruere and Marc Power on ResonanceFM 104.4
  15. Try Kramer, they do this sort of junk
    for example:

  16. Cheapest I can find is around $380 ie about 10x the price I can make
    the boards for myself. Additionally, they don't even have XLR
    connectors which I had budgeted for in my own design costing.
    Now you have definately convinced me to do my own :-(
    Maybe I'll offer the board for sale as well.

  17. Are you going to reclock, etc?
    and what was the price of the Kramer? Nothing on the site,
    that i could find

  18. The $380 was the cheapest I could find for the Kramer.
    And yes, I will be reclocking since the other ends feed into DSP based
    I'm resigned to the fact that I won't find what I want at a reasonable
    I've sketched up a design based on what I wrote above and will
    breadboard it this week. If it's OK I'll do a cheapo layout and get a
    oneoff PCB manufactured with XLR connector positions etc. Probably
    take me the best part of a week altogether, but since we will
    eventually need around 100 it looks like it will save us some $30,000
    over the next year.

  19. And Kramer is the bottom of the food chain..... 380$, ouch
    Are you using the CS8406/CS8416 to re clock, or something more
    If you are using transformers, it may be cheaper to wind your own,
    more info on epanorama, the commercial ones seem to be a rip off

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