SPDIF amplifier
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From: Hawker on 1 Mar 2007 20:26 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 Hawker On 3/1/2007 12:13 PM, The digits of Dirk Bruere at NeoPax's hands composed the following: > On 1 Mar, 16:19, Hawker > <Hawker{removethispa...(a)ashevillecommunity.org> wrote: >> 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. > > 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? > > Dirk >
From: cs_posting on 1 Mar 2007 23:45 On Mar 1, 11:00 am, "Dirk Bruere at NeoPax" <dirk.bru...(a)gmail.com> wrote: > 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). 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.
From: Dirk Bruere at NeoPax on 2 Mar 2007 06:01 Hawker wrote: > 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. > The three machines that need the AES signal are in different locations. -- Dirk http://www.onetribe.me.uk - The UK's only occult talk show Presented by Dirk Bruere and Marc Power on ResonanceFM 104.4 http://www.resonancefm.com
From: Eeyore on 2 Mar 2007 09:12 Dirk Bruere at NeoPax wrote: > 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). A video DA should be OK to distribute SPDIF but the signal voltage of SPDIF is too low for AES. Graham
From: Dirk Bruere at NeoPax on 2 Mar 2007 11:09 On 2 Mar, 14:12, Eeyore <rabbitsfriendsandrelati...(a)hotmail.com> wrote: > Dirk Bruere at NeoPax wrote: > > > 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). > > A video DA should be OK to distribute SPDIF but the signal voltage of SPDIF is > too low for AES. > > Graham 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 isolation. 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) http://www.epanorama.net/documents/audio/spdif.html Opinions? Suggestions? Maybe I'll sell some as a sideline... Dirk
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