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Video DA IC?
MUFF WIGGLER Forum Index -> Video Synthesis  
Author Video DA IC?
fletch
I'm wondering if video distribution amplifiers exist as an IC, or if people generally design simple circuits with regular video op-amps. I was thinking of building the following circuit that I found in an old Leitch manual, but wondering if it could be simplified using op-amps.

daverj
Video op amps are used these days.

On the other hand, video DAs are so cheap pre-made, that it's not really worth the cost and time to build one.

https://www.google.com/#q=video+distribution+amp
lizlarsen
I'd definitely second that. You won't save any money doing it yourself. A bunch of video op-amps will do the trick though. 75 ohm termination on the single input, going into a bunch of gain x2 non-inverting amplifiers, and driving 75R outputs.
fletch
Cool, thanks. Yeah the thing is, I'd like to build it into a Euro module, much like audio multiples. I suppose I could order a cheap DA and try to mount it behind a panel but I think it might be too big. At $7 a pop though, it would be worth trying.

How many outputs do you think a single op-amp could drive?
lizlarsen
LM6172 specifies 50mA of output current per channel, and I believe power consumption for a 75 ohm driver is about 13.5mA? Sounds like you could safely drive 3 outputs per channel. So with LM6172 using both channels, you could get 6 outputs. Power consumption would be about 80-90mA I suppose.



We're planning to do a slim 4HP distribution amp module like this at some point, but it hasn't been a priority yet (due to the availability of external DAs for so cheap.)
daverj
Most video op amps are designed to drive a single terminated video output. So a dual op amp chip will drive two outputs, two dual chips drive 4 outputs, etc...

It's a good idea to use one amp as an AC coupled receiver and have it drive the rest of the amps, which are set as 2x gain and have a 75 series resistor on their outputs. So in that configuration 2 chips gives 3 outputs, 3 chips gives 5 outputs, etc...

If you are interested in buying such a module instead of building it, I have boards already etched for something like this. It's a bit different but could be modified into what you want. It's a black burst distribution amp for my modular video system, with inputs on the back and 5 outputs on the front. I could build one with one of the outputs on the front converted to the input. So it would be 1 in and 4 out.

I haven't worked up a price yet, and it certainly wouldn't be as cheap as those mass produced ones, or building it yourself. I also don't have metal panels made yet, but could laser cut a wood or acrylic one.

lizlarsen
Dave's advice on the number of op-amps you can use per input is probably much better than my own. The engineering half of LZX is my partner Ed, and my own knowledge is fairly marginal compared to his or Dave's. In any case, the schematic I posted may not be the ideal circuit, but it will still probably do the job.
fletch
cool, thanks fellas!
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