nevster1975 Posted September 30, 2007 Share Posted September 30, 2007 I just bought some AR133s di's and used them for the first time this morning. I used one of them for a bass guitar and was taking the link out jack output into an on-stage amp and the XLR output to a multicore. There was a horrible hum from the amp. When the bass was plugged into the amp directly the sound was fine. We did some testing afterwards and found that when the DI box was connected up without the XLR connection to the multicore (i.e. jack in and link out to amp) the sound was fine. It was only when we plugged the XLR output in and connected it to the desk that we got the hum on the amp. This without the desk even being switched on so operating in 'passive' mode. We got exact same thing with another DI box as well (orchard electronics). I do also have a Behringer VTone ADI21 accoustic DI and this one was the only one that was ok and didn't give a hum when we connected the XLR. The only difference between the 3 DIs is that the VTone isn't phantom powered, although as stated we would get the hum with the other two DI's just when connected it to the desk via the multicore, with the desk powered down. As you can imagine, can't understand the origin of the hum, but would like to get rid of it without having to use the Behringer DI. Any ideas? It seems like it must be some sort of earth hum, but I can't understand why the Behringer would be OK? Any ideas much appreciated. Operating the ground lift on the AR133 didn't do anything at all and the orchard electronics box doesn't have a ground lift. It's a really weird one, but we tested it fairly systematically.. Any ideas gratefully received.... Link to comment Share on other sites More sharing options...
Ben Langfeld Posted September 30, 2007 Share Posted September 30, 2007 Might help to know what desk you have and what your power arrangements are. Link to comment Share on other sites More sharing options...
mackerr Posted September 30, 2007 Share Posted September 30, 2007 It was only when we plugged the XLR output in and connected it to the desk that we got the hum on the amp. This without the desk even being switched on so operating in 'passive' mode.What happens when you turn on the mixer? What happens when you change the pin 1 lift switches on the various DIs? If the mixer was turned off, how were you powering the DIs that require phantom power? Mac Link to comment Share on other sites More sharing options...
Shez Posted October 1, 2007 Share Posted October 1, 2007 If the mixer was turned off, how were you powering the DIs that require phantom power? AR133s have internal 9v batteries for power in the absence of phantom. Link to comment Share on other sites More sharing options...
dbuckley Posted October 1, 2007 Share Posted October 1, 2007 Thats DI isn't sitting on top of the amp is it? Could be coupling from the amp mains transformer to the DI box transformer, for those DI boxes with transformers in them. Try relocating the DI box. Normally hum is an earth loop, and operating the earth lift switch vanquishes it, but in your case it apparently doesn't, so a more left field suggestion is called for... Link to comment Share on other sites More sharing options...
Arran Posted October 1, 2007 Share Posted October 1, 2007 Are your backline and FOH using different mains supplies? Is your multicore fully ballanced: XLRs both ends, discrete earths? Link to comment Share on other sites More sharing options...
mackerr Posted October 1, 2007 Share Posted October 1, 2007 If the mixer was turned off, how were you powering the DIs that require phantom power?AR133s have internal 9v batteries for power in the absence of phantom.As do most phantom powered DIs, but the OP implied that the DI was phantom powered, and we have no way of knowing whether or not he had a battery in the DI. Only he can answer that question. Mac Link to comment Share on other sites More sharing options...
nevster1975 Posted October 2, 2007 Author Share Posted October 2, 2007 Thanks for all the comments so far. Re: phantom power -- the desk was off so the DI was not powered when we were doing the testing on this, but of course it was still passing a signal via the link and it was when we connected the di XLR out to the desk that we got the hum. (we also of course got it with the desk powered up as well) the di is connected to the desk via a multicore, all balanced. The desk is an a&h mixwizard 16:2. It is plugged into a separate socket to the amp. the di isn't on top of the amp, or that near it. I guess one of my questions is what's the difference between the behringer di and the ar133 electronically because one has the hum the other doesn't. Link to comment Share on other sites More sharing options...
noiseman Posted October 2, 2007 Share Posted October 2, 2007 Sounds like a ground loop.The desk, although not turned on would still have been connected to earth. Try unplugging the desk and any other stuff attached to it.You should run all power from the same supply. Even though you may think that the sockets are on the same circuit, this is not always true. Link to comment Share on other sites More sharing options...
nevster1975 Posted October 2, 2007 Author Share Posted October 2, 2007 Sounds like a ground loop.The desk, although not turned on would still have been connected to earth. Try unplugging the desk and any other stuff attached to it.You should run all power from the same supply. Even though you may think that the sockets are on the same circuit, this is not always true. Thanks -- I can try the same experiment with the desk unplugged, but it doesn't really help the set up to try and get everything on the same circuit as the desk is at the back and the amp is at the front -- should I run an extension cable down to the front to power the amp? I still don't understand though why the behringer di wouldn't give the buzz..... no clues as to that so far in terms of their design. Link to comment Share on other sites More sharing options...
mackerr Posted October 2, 2007 Share Posted October 2, 2007 I'm still curious if there was any difference when you tried different settings for the pin 1 lift switch on the DI. That would be the first thing I would do if there was hum or buzz on a DI. Mac Link to comment Share on other sites More sharing options...
noiseman Posted October 2, 2007 Share Posted October 2, 2007 should I run an extension cable down to the front to power the amp? It is common practice to run power from the stage to FOH, usually by taping a mains cable alongside themulticore. This should not cause any interference. Good luck. Link to comment Share on other sites More sharing options...
nevster1975 Posted October 3, 2007 Author Share Posted October 3, 2007 I'm still curious if there was any difference when you tried different settings for the pin 1 lift switch on the DI. That would be the first thing I would do if there was hum or buzz on a DI. Mac Thanks Mac -- per my original post I did try changing the ground lift switch on the DI (AR133) to no effect.... Link to comment Share on other sites More sharing options...
CPlater1 Posted October 3, 2007 Share Posted October 3, 2007 Did you have it set up as follows? Bass --> DI Box line in to thru --> Amp As sometimes the thru output on DI boxes isn't the greatest in the world, and some I have used don't lift the ground on the thru socket. You could try putting the DI box after the amp, as a) most of the time you still get the amp sound, and b) this could possibly solve your problems. If the amp has a headphone jack, that normally cuts off the speaker, but if it has a line out jack, then this is what you will probably want to use. Link to comment Share on other sites More sharing options...
Ben Lawrance Posted October 3, 2007 Share Posted October 3, 2007 Mic the bass cab, better sound without the hum. Link to comment Share on other sites More sharing options...
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