SPDIF amplifier

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.

Hawker

On 3/1/2007 11:00 AM, The digits of Dirk Bruere at NeoPax's hands composed the following:

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

Thanks Dirk

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

What about a distribution amp for VGA video?

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

CobraNet......?

QSC Rave, Routing Audio Via Ethernet......

DNA

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:

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.

The three machines that need the AES signal are in different locations.

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 encounter).

Opinions?

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.

Try Kramer, they do this sort of junk for example:

martin

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.

Dirk

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

martin

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 systems. I'm resigned to the fact that I won't find what I want at a reasonable price. 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.

Dirk

And Kramer is the bottom of the food chain..... 380$, ouch Are you using the CS8406/CS8416 to re clock, or something more sophisticated? 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

martin

It will be feeding into SHARC based equipment that will do the reclocking along with a whole bunch of stuff.

I can get them for around $5 each, one off. Here's an expensive version:

T. Giesberts from Elektor Electronics magazine July/August 1995 pages

your local transformer dude could save you a some.

(stolen from

martin

I've looked at those circuits and don't feel too happy about feeding a signal that could only be 0.2V (or even less?) into an HCU04

Yabut... they/he uses the 04 in a linear mode, note the feedback resistors

martin