Humey Posted November 24, 2010 Share Posted November 24, 2010 I have an upcoming event in which videos will be projected via a laptop. The problem I have is that the laptop and projector will be on stage, and the audio will need to be played via the PA which is controlled in the lighting box. My solution to this was to create a 3.5mm stereo jack to 2 XLR, run this to the stage box. Does anyone have the wiring diagram for me to make this cable? Or does anyone have a better solution? Link to comment Share on other sites More sharing options...
stevefez Posted November 24, 2010 Share Posted November 24, 2010 A better solution would be to create (buy) a 3.5mm TRS to 2x TS 6.25mm (1/4") jacks. Then run these into a pair of DI boxes, and from there, to the stagebox etc... This would make sure the signal runs balanced for the majority of the distance. Link to comment Share on other sites More sharing options...
ramdram Posted November 24, 2010 Share Posted November 24, 2010 www.soundcraft.com/support/fetchpalz.aspx?cat_id=guides&id=1812 http://www.mediacollege.com/audio/connection/ http://www.laventure.net/tourist/cables.htm Probably more than you need on the connector gen. Just keep an eye on levels. HTH Link to comment Share on other sites More sharing options...
Humey Posted November 24, 2010 Author Share Posted November 24, 2010 unfortunatly its pretty much out of the question for me to buy anything. I don't have a DI box (department won't let me purchase any!). Is the DI box vital? Link to comment Share on other sites More sharing options...
MarkPAman Posted November 24, 2010 Share Posted November 24, 2010 Is the DI box vital? If you're very lucky you may be OK without one. It doesn't have to be a DI box though, just something that can give you a balanced output. Have you got a small mixer or a graphic eq that would give you balanced outputs? Though these probably would not have an earth lift, which is something you may, or may not, need. Link to comment Share on other sites More sharing options...
revbobuk Posted November 24, 2010 Share Posted November 24, 2010 And be aware that if you don't use a DI box you should make sure that phantom power is switched off for the input you are using. You don't want 48v up the laptop output! If the laptop will be running on mains power, then digital hash noise from the switched-mode PSU will very likely be audible on the output. Search this forum for ways of dealing with it. Link to comment Share on other sites More sharing options...
Bobbsy Posted November 24, 2010 Share Posted November 24, 2010 unfortunatly its pretty much out of the question for me to buy anything. I don't have a DI box (department won't let me purchase any!). Is the DI box vital? Well, as Mark says, you may be lucky. However, a quick search of previous threads will show you just how often people have problems with laptop audio being patched into sound systems--it's a very common topic. Add to the normal laptop issues the fact that your way will have a very long unbalanced run and the sound gear in the lighting booth will very likely be on a different mains circuit and the scope for problems is pretty bad. If you can get access to all the gear and try everything out well before hand (i.e. with time to rent extra gear if needed) then it's worth an experiment. However, I certainly wouldn't want to just go in cold with an audience waiting--the scope for problems is just too great. Bob Link to comment Share on other sites More sharing options...
David Lee Posted November 24, 2010 Share Posted November 24, 2010 unfortunatly its pretty much out of the question for me to buy anything. I don't have a DI box (department won't let me purchase any!). Is the DI box vital? http://www.thomann.de/gb/behringer_di20_di_box.htm at about £16 you could get one for your own personal use. (though this item is listed as sold out I am sure you can get it from other retailers. Or get 2 x the cheaper single channel ones. Link to comment Share on other sites More sharing options...
Humey Posted November 24, 2010 Author Share Posted November 24, 2010 Thanks guys, I hadn't thought this through, especially the Laptop power noise and the fact sound equipment will be on a different mains circuit. Link to comment Share on other sites More sharing options...
andrewg112 Posted November 24, 2010 Share Posted November 24, 2010 I have had this problem before! When having the laptop powered, it creates a horrible hum that is very loud, and unbearable. For us the way to do this was to have a laptop running on the battery. This reduced the hum alot, but there still was a little buzz. Eventually having the laptop in the control room made more sense, as we had a long VGA cable and could unplug it when there was no sound. I have to support whats already been said, in that you really should invest in something to sort the problem out. Id be off for a little trip to maplins for about £5 and that should sort out your converter. They also do a product for earth loop hums which I never tried, but I would advise doing! Regards,Andy Link to comment Share on other sites More sharing options...
boswell Posted November 24, 2010 Share Posted November 24, 2010 http://cpc.farnell.com/jsp/search/productd...jsp?SKU=AV12774 Just over £5 inc VAt, they work well. Link to comment Share on other sites More sharing options...
paulears Posted November 24, 2010 Share Posted November 24, 2010 If you really have to get unbalanced laptop audio into a computer - then run it mono, and ignore the XLR earth pin (1) putting just one side - use the tip of the 3.5mm plug to pin 2 of the XLR, and the screen to pin 3. This breaks the earth and usually works - BUT don't expect to be able to use the ring and earth to another XLR because you are joining the pin 3 connetions of two channels and many desk really don't like this. Soundcrafts can suddenly produce odd oscillations and weird noises, and trying this on an Allen & Heath made the channel gain controls very temperamental. If you can live with mono - it's much better than trying to run unbalanced (ESPECIALLY if you have a Dell like mine - who's power supply seems specially designed to produce all kinds of odd noises in the system!) Link to comment Share on other sites More sharing options...
TomHoward Posted November 24, 2010 Share Posted November 24, 2010 To advise on the original question - if you're making a minijack to XLR cable, don't bother soldering the minijack connector. Get a minijack-whatever cable with figure 8 cable, and cut the other end off. Wiring wants to be tip & ring to Pin 2 on each XLR connector (tip would be left, ring would be right) and join the screen to either pins 1 & 3, or just 3 if you want to lift the earth as Paul suggests. That said, you can buy a cheap minijack - 2x XLR lead for less than £2 from CPC, which might be the easiest way. Link to comment Share on other sites More sharing options...
james.sealey Posted November 24, 2010 Share Posted November 24, 2010 And be aware that if you don't use a DI box you should make sure that phantom power is switched off for the input you are using. You don't want 48v up the laptop output! I've seen (and smelt) the after effects of a 3.5mm Jack to XLR lead when used to plug an ipod into a desk with global phantom power - not good - and for that reason I will never make, nor advise anyone to make a lead of that nature! Link to comment Share on other sites More sharing options...
TomWeston Posted November 25, 2010 Share Posted November 25, 2010 And be aware that if you don't use a DI box you should make sure that phantom power is switched off for the input you are using. You don't want 48v up the laptop output! I've seen (and smelt) the after effects of a 3.5mm Jack to XLR lead when used to plug an ipod into a desk with global phantom power - not good - and for that reason I will never make, nor advise anyone to make a lead of that nature! yes I have a few friends who have now had to send their macbooks in for new logic boards as a result of this ! Damn phantom power Link to comment Share on other sites More sharing options...
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