|
Post by steveb on May 11, 2009 8:31:28 GMT
This subject was posted on the old forum, but I thought I would put it out there again, My lap top is connected to the PA from the head phone jack socket to a jack plug into the PA, which causes a buzz through the PA while the power cable is connected. (disconnect the power cable and the buzz goes away) Someone suggested to use a USB plug from the laptop and a cannon fitting in the PA will solve the problem, but is there such a cable available or does it have to be made up.
|
|
kemo
Full Member
Yes, it's only me.
Posts: 643
|
Post by kemo on May 11, 2009 9:49:06 GMT
Easiest fix is to remove the earth from your power adaptor, or if you do not wish to carry this out I'd suggest you pick up one of those little three pin to two pin power adaptors, this will solve the buzzing issue.
|
|
|
Post by JohnG on May 11, 2009 12:06:18 GMT
Removing the connection to the Earth pin on the laptop power supply is almost certain to cure the problem but is NOT deemed to be the safe way to do it, as the power supply itself then becomes a potential safety hazard as does any exterior metalwork on the laptop which is connected to earth. 3.5 Amps at 19 Volts is enough to kill you if a fault develops! You have been warned!It's also enough to mess up a lot of electrical circuitry if it finds its way through to the mixer or other pieces of equipment. A better way to do it is with a double insulated power supply. These will have a plastic earth pin or, if they have a continental 2 pin connector, are almost certain to be double insulated anyway. If that's what the problem is. You can often tell whether the mains cable is carrying an earth depending on whether it is flat or round. The round one has 3 conductors in it, the flat one only two. The approved way is to use a line level DI adapter on the audio connector, the DI box must have an "earth lifter", which you use to remove the earth loop on the audio leads. This is the safe way. There is a whole thread on this issue on the Sound-on-Sound site, see here: www.soundonsound.com/forum/showflat.php?Cat=&Number=222392&page=0&view=collapsed&sb=5&o=&fpart=1#222392There is also a whole stack of DI boxes here: www.thomann.de/gb/cat.html?gf=di_boxes&oa=praSorry to throw a spanner in the works Kemo! Stay safe, JohnG.
|
|
|
Post by JC on May 11, 2009 12:17:15 GMT
My laptop doesn't have an earth pin on the Power Supply
|
|
|
Post by steveb on May 12, 2009 7:20:07 GMT
That's an excellent article at Sound on Sound John, (thank you once more) and I recommend anybody having laptop noise to read it.
|
|
|
Post by JohnG on May 12, 2009 8:57:04 GMT
Hi Steve, Thought I'd post the answer to your PM here so that everyone can read it. i.e. which DI box is the one for me? Of course the output from a laptop is usually stereo in the form of a 1/8" TRS mini jack plug. Stereo means two channels (yea, I know you knew that, I just thought I'd remind you ), but that means we will need a two channel DI box. If you check on the pages of Thomann's site that I posted, you will see that the cheapest 2 channel one is the DI20 from Behringer. Now, I haven't used this piece of kit myself, so I can't personally recommend it, but I know a couple of people who have, who also used it to get over the laptop buzz problem. They both reported first class results. However, the sting in the tail! There's always one of those isn't there? You're probably currently using a 1/8" to 2 x 1/4" jack plugs (TRS balanced or TS unbalaced) cable, into the mixer. This type of lead will probably do to go into the DI20, then you'll need XLRs out of the DI20 to the appropriate connector type for your mixer. You'll need to talk to your sound engineer if you're unsure about this. Remember a DI box is usually made to take the output direct from a guitar (i.e. not via the guitar amp) and input it into the mic input of the mixer. The line output of a laptop is a LOT higher than a guitar, so you may have to use some of the signal attenuation which is switchable on this unit. It looks like the Millenium DB400 might do the job too, but the ART Cleanbox II looks as if it has been made more specifically for this function and the Millenium PCX 2 spec. even talks about connection of a PC. But these are all progressively more expensive than the DI20. Here's a pointer to the DI20 page: www.behringer.com/EN/Products/DI20.aspxwhere you'll find the pdf of the manual too. Take a look at this article (especially at the foot of the page) about solving computer audio problems: www.soundonsound.com/sos/nov04/articles/computerproblems.htmMartin Walker is The Real Guru when it comes to this stuff. Hope that's of some help? JohnG.
|
|
|
Post by JazzCat on May 13, 2009 5:30:20 GMT
Thank's John, for posting the reply here. It's much appreciated. When questions go to PM's that takes the rest of us, who very well could learn something quite important, right out of the loop.
|
|
|
Post by JohnG on May 13, 2009 6:48:46 GMT
My pleasure, as always JazzCat.
So, just a few final words on this.
To go from the laptop to the DI20 you are most likely to need a cable which has a 1/8" TRS (Tip, Ring, Sleeve) or stereo jack plug at the laptop end to a pair of 1/4" TS (Tip, Sleeve) or TRS jack plugs for the box. In other words one that splits the stereo output of the laptop into its left and right channels.
I'll stick a picture of the cable in here when I've taken one.
As the output of the DI20 is an XLR (microphone) socket, and if we are going to plug the output into the same socket on the mixer, then we will need two cables with an XLR on one end and a 1/4" jack plug (TS or TRS, it will depend on your mixer inputs) on the other.
Again I'll put a picture of the cable here when I've taken one.
You may need to turn down the signal level by using the attenuator switch on the DI20.
I think I may actually order one of these little chappies to find out how well it works with my setup.
JohnG.
|
|
|
Post by steveb on May 13, 2009 11:02:26 GMT
Thanks John, Instead of using the small stereo jack plug at the laptop, could you use the laptops USB and then go into the DI box?
|
|
|
Post by steveb on May 13, 2009 11:08:44 GMT
Further on from that John, Can the cable, be mono, from the DI box to the PA XLR input? as the PA we are using is Mono
|
|
|
Post by JohnG on May 13, 2009 13:59:51 GMT
Hi Steve,
What comes out of the USB port directly is digital so it can't go into a DI box without first being converted to an analogue audio signal.
If you are going mono then you probably don't need the DI20 but a single channel DI box with a ground lifter. If you pan everything to the left or right in the MIDI file to get the mono signal and feed the appropriate plug of the pair into a DI box then out to the mixer input.
Please remember I am only passing on advice about DI boxes from what I found out from others. Until I use one myself I can't be much more specific.
JohnG.
|
|
|
Post by moonie on May 18, 2009 10:58:09 GMT
Hi All I thought I would add that this link www.arx.com.au/International/audibox_usb_di_apps.htmA transformer isolated di for converting a usb port to be your audio port instead of using the tiny laptop audio out that can be easily damaged... I haven't used one but a friend swears by it...and he's very fussy. cheers
|
|
|
Post by JohnG on May 18, 2009 12:09:14 GMT
Thanks for posting that Moonie,
I hadn't seen one of those before. I expect the quality is rather good as the signal remains digital until it enters the DI box, where it gets converted to analogue, away from all the interference inside a laptop. Only problem is that it seems to list for £119 over here, which seems a bit steep!
JohnG.
|
|