passive split on a composite signal

[obaka-san]

Hi guys. I'm sure this topic must come up a fair bit however my searches both here and on google didn't come up with much.

 

I'm a soundie in training and an amdram group I work with has asked me if I could set up some extra monitors in the pit/backstage running of off the venues in house stage camera (normaly feeds directly to a monitor in prompt corner). I know this would be easy peasy and (mostly) trouble free with a proper distribution amp however, due to quick and dirty nature of the desired setup and the ever present budget constraints I'm wondering if I could get away with making up a simple 1-in 4-out break out box.

 

I relise I WILL have a loss in picture quality and it's not best practice but I am unsure as wether or not there will be major problems with ghosting/artefacts/etc.

 

Thanks for any help,

Kieran

 

P.S does anyone have any schematics for a distro amp? I'm not having much luck with google. If it's something simple like a unity gain op-amp buffer a DIY one would be a handy addition to the tool bag

[boatman]

You can do a passive split with 5 off 45 ohm resistors (47 ohms is close enough) connected as a star. Unfortunately, you will get a 12dB loss on each output so you will need to crank up the contrast on the monitors.

 

The are lots of video circuits in Application note 57 from Linear Technology or on this page from ePanorama.net.

 

HTH.

[obaka-san]

Thanks for that. Just to clarify, the passive split would use a resistor on the 'hot' pin of each plug and then be ganged together?

[Chris Beesley]

Did you know there are amplifiers on the market V cheap... http://cpc.farnell.com/_/210-903/video-amp...tter/dp/AV11812 - not the highest qualityunit but they do work!

[obaka-san]

Did you know there are amplifiers on the market V cheap... http://cpc.farnell.com/_/210-903/video-amp...tter/dp/AV11812 - not the highest qualityunit but they do work!

 

DOH!!! just checked ebay and those units are available shipped for about $20

 

I live in australia and the usual suspects over here want 100aud (about 50gbp) for cheapo chinese units which personaly seems a bit over the top

 

Thanks for the idiot check,

Kieran

[boatman]

Thanks for that. Just to clarify, the passive split would use a resistor on the 'hot' pin of each plug and then be ganged together?

 

Yes, like this:

 

      45R         45R
IN  -|___|--o----|___|- OUT
            |
            |     45R
            o----|___|- OUT
            |
            |     45R
            o----|___|- OUT
            |
            |     45R
            +----|___|- OUT

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

 

That gives you a constant impedence of 75 ohms for all inputs and outputs, but an attenuation of 12dB for each output.

[paulears]

12dB down on the sync pulse can really upset some monitors. Buying the bits to make one, unless you have the components laying around makes buying one a sensible thing!

[back_ache]

could set up some extra monitors in the pit/backstage running of off the venues in house stage camera (normaly feeds directly to a monitor in prompt corner)

 

Are they proper monitors with switchable termination and bnc connectors, if so you may be able to daisy-chain them using t-pieces.

[obaka-san]

could set up some extra monitors in the pit/backstage running of off the venues in house stage camera (normaly feeds directly to a monitor in prompt corner)

 

Are they proper monitors with switchable termination and bnc connectors, if so you may be able to daisy-chain them using t-pieces.

 

 

 

just bog standard tv's. I reckon I'll pick up a couple of these to add to my stash of little black boxes, bit hard not to at the price B-)