Members mikekars Posted March 22, 2014 Members Share Posted March 22, 2014 I am trying to get a sense of how safe it is to plug keyboards directly into the mixer line level inputs. I have a digital mixer that allows me to effectively increase the channel count if I use the aux inputs for line level sources. I am looking for input from folks that provide sound for whomever shows up, rather than a fixed band situation. My concern is not so much that there might be a "hum" problem. It is more that some electrical fault on the keyboard could damage my mixer. I generally like to establish clear electrical boundaries between me and the musos. I have lots of DI boxes but they only let me plug something into the mic inputs, which sometimes are in short supply. Do I need to buy a few 1:1 line level isolation transformers so I can plug into the aux inputs or is it safe to plug random line level sources directly into those? I would just "buy 'em" but I already come loaded for bear and don't use half the stuff I bring. Plus I am trying to stop that habit. Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 22, 2014 Members Share Posted March 22, 2014 Never, my console is 125 feet from the stage. If the inputs are TRS balanced and they give you a headphone feed (thinking it's just line level) it won't work since the common L/R program will be cancelled by the balanced input. Link to comment Share on other sites More sharing options...
Members Drummer44 Posted March 22, 2014 Members Share Posted March 22, 2014 We usually do. Usually it's just a short run, and we use the balanced XLR outputs from the keyboard to balanced XLR In on the mixer anyway. -D44 Link to comment Share on other sites More sharing options...
Members RoadRanger Posted March 22, 2014 Members Share Posted March 22, 2014 I often do - but I make sure the keys are plugged into the same circuit as the mixer and the cords are relatively short. As my DL1608 mixer goes on the stage or sidestage that's pretty easy to do. Link to comment Share on other sites More sharing options...
Members Stingray5 Posted March 22, 2014 Members Share Posted March 22, 2014 RoadRanger why the same circuit as the mixer? Ground Loop? Link to comment Share on other sites More sharing options...
Members RoadRanger Posted March 22, 2014 Members Share Posted March 22, 2014 ^ I'd tell you but you can't quote comments here . But yah, unbalanced connections require that you insure there is no difference in the grounds between the devices at both ends. Link to comment Share on other sites More sharing options...
Members mikekars Posted March 22, 2014 Author Members Share Posted March 22, 2014 Wouldn't the cancellation problem from a "headphone" output be a problem even with a DI box if you don't use the right connection or cable? I think I understand that issue and do have cables that will split a "headphone" output into two separate signals. I am just wondering if best practice is to try to electrically isolate my gear from the musician's gear? Or is is generally safe to plug the random keyboard directly into the mixer. It is sort of the same issue with a bass amp with a DI out. I have often worried that some sort of fault in the bass amp could damage my mic input channel or worse. I use a digital mixer and my experience so far is that they are touchy with regards to any kind of electrical glitches. Link to comment Share on other sites More sharing options...
Members Stingray5 Posted March 22, 2014 Members Share Posted March 22, 2014 RoadRanger. Did I do something wrong? Link to comment Share on other sites More sharing options...
Members wesg Posted March 22, 2014 Members Share Posted March 22, 2014 Right, "headphone cancellation" will happen any time you try to use the headphone output with a TRS plug into a mono balanced input. For those keyboards using the headphone output as a line out (many Yamahas do, for example), you need to either go with a TS patch cord directly into the mixer, OR convert it to balanced (with a keyboard amp, DI, etc) before plugging into the board/snake. Going unbalanced into the snake without proper conversion (transformer or op-amp "servos") is a loser. Keyboards which use an external DC "brick" power supply with a two-prong plug should not give you any ground loop problems, even with an unbalanced connection, as they have no ground reference of their own. But running more than 20 feet unbalanced is something I try very hard to avoid. I avoid it in my rig by not owning any cables longer than that. I have a Yamaha DGX-620 which has a DC brick and a headphone output. I normally run it in mono with TS, but occasionally I decide to go stereo (if FOH is stereo). When I do I use a TRS->2xTS adapter and run two TS patch cables back to the board. If I'm at a venue that supplies a snake and a stereo PA (rare rare rare) I will use an insert cable plugged into a stereo DI (or DI pair) and feed two balanced runs to the snake. I would expect you can plug any keyboard which provides balanced XLR outputs directly into your snake/board without any isolation, although transformers never hurt. I would love to hear from anybody with experience with these. Wes Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 22, 2014 Members Share Posted March 22, 2014 Wouldn't the cancellation problem from a "headphone" output be a problem even with a DI box if you don't use the right connection or cable? I think I understand that issue and do have cables that will split a "headphone" output into two separate signals. I am just wondering if best practice is to try to electrically isolate my gear from the musician's gear? Or is is generally safe to plug the random keyboard directly into the mixer. It is sort of the same issue with a bass amp with a DI out. I have often worried that some sort of fault in the bass amp could damage my mic input channel or worse. I use a digital mixer and my experience so far is that they are touchy with regards to any kind of electrical glitches. Yes, correct. Plugging directly into the board is just so inviting that it's easily overlooked. Yes, it's always best practice to transformer isolate from stage gear, especially if they might be sensitive to the effects of phantom power (there are still some units that do not have protection from phantom power... amazing but true.) Link to comment Share on other sites More sharing options...
Members mikekars Posted March 22, 2014 Author Members Share Posted March 22, 2014 It is sort of what I thought - that it would be best practice to always try and electrically isolate my gear from the musicians gear. I do generally go down a snake so another reason is to get any unbalanced signals converted to balanced. When using a DI box with keyboards, acoustic guitars, etc, this has all been pretty straight forward. Both passive and active DI boxes do a good job of accepting a wide range of input levels and converting to mic level. They also exhibit high input impedance so they don't load down the source signal. However, to use my mixer's line level inputs I need a 1:1 isolation transformer. These isolation transformers like the Ebtech hum eliminator, rapco isoblox, ART cleanbox, and the like seem to have an input impedance of 600 ohms or so. So this is another area of confusion for me. Isn't that a low enough impedance to potentially overload the source signal? That is a dramatic difference from the 10-50k ohms the source would see if plugging directly into the mixer. Link to comment Share on other sites More sharing options...
Members RoadRanger Posted March 22, 2014 Members Share Posted March 22, 2014 RoadRanger. Did I do something wrong? Not really, whomever set up this software has yet to disable comments as was promised a couple weeks ago. In general use "quote" instead of "comment", comments might just disappear when they get around to that (or not?). Link to comment Share on other sites More sharing options...
Members Stingray5 Posted March 22, 2014 Members Share Posted March 22, 2014 Not really, whomever set up this software has yet to disable comments as was promised a couple weeks ago. In general use "quote" instead of "comment", comments might just disappear when they get around to that (or not?). OK I got it .Thanks Link to comment Share on other sites More sharing options...
Members Drummer44 Posted March 22, 2014 Members Share Posted March 22, 2014 I often do - but I make sure the keys are plugged into the same circuit as the mixer . Yep, forgot to say, that too... -D44 Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 22, 2014 Members Share Posted March 22, 2014 1:1 transformers reflect the load impedance to the primary of the transformer. The 600 ohms implys that the transformer's core is capable of handling a 600:600 ohm transformation, but if you put a 10k load on the secondary the primary will look like between 5k and 10k. Link to comment Share on other sites More sharing options...
Members mikekars Posted March 22, 2014 Author Members Share Posted March 22, 2014 Aha - that is why they work in so many situations. Ebtech here I come. If you had a mic level source such as a DI out from a bass amp, could a 1:1 isolation transformer be inserted between that source and the snake without degrading the signal? If so then that could be a way to protect my gear from amps where the musician offers me a DI out. I realize this is possibly a lot of over thinking and complicating what should be a simple connection, but in my limited experience I have seen some very poorly maintained equipment. At my level it seems the musicians don't have the funds to keep their gear in good repair. Lots of loose flaky jacks, amps that buzz like you shouldn't touch them without insulated gloves, and plenty of cut off ground prongs on the ac plug. I am just trying to "insulate" my gear from these sorts of problems as much as I can. Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 23, 2014 Members Share Posted March 23, 2014 Aha - that is why they work in so many situations. Ebtech here I come. If you had a mic level source such as a DI out from a bass amp, could a 1:1 isolation transformer be inserted between that source and the snake without degrading the signal? If so then that could be a way to protect my gear from amps where the musician offers me a DI out. I realize this is possibly a lot of over thinking and complicating what should be a simple connection, but in my limited experience I have seen some very poorly maintained equipment. At my level it seems the musicians don't have the funds to keep their gear in good repair. Lots of loose flaky jacks, amps that buzz like you shouldn't touch them without insulated gloves, and plenty of cut off ground prongs on the ac plug. I am just trying to "insulate" my gear from these sorts of problems as much as I can. Yes, this is a common use, and most are wound so that mic level is ok (shielding can be an issue sometimes but usually a minor problem compared to what you are protecting yourself from). Isolation transformers go onto all outputs that I do not have 100% confidence in... ESPECIALLY video idiots. (Looks like a clearcom cable, let's plug it in and try it. Seen a few damaged consoles from this. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted March 23, 2014 Members Share Posted March 23, 2014 Simple1/4 out from keyboard > DI > Xlr > Snake and or Mixer. Link to comment Share on other sites More sharing options...
Members twostone Posted March 24, 2014 Members Share Posted March 24, 2014 Simple 1/4 out from keyboard > DI > Xlr > Snake and or Mixer. ^ This is what I do when dealing with Keyboards and E-drums to. Link to comment Share on other sites More sharing options...
Members Iamthesky Posted March 24, 2014 Members Share Posted March 24, 2014 I am constantly amazed how hard it is to get people to understand the difference between a headphone TRS and a balanced TRS, and why you can't just plug one into the other. Link to comment Share on other sites More sharing options...
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