Loud hum when using outputs 1-4

marcdeben · Post by **marcdeben** » Sat May 02, 2015 2:45 am

Hi all, When I send a drum track out the 1/2 outputs, I get a loud hum. No hum out the main outs and have tried a few cords with the same issue. Are these outputs stereo jacks?
Thanks

apex · Post by **apex** » Sat May 02, 2015 5:45 am

No they are mono jacks.

awyatt1 · Post by **awyatt1** » Sat May 02, 2015 3:06 pm

The 1-4 individual outputs can be used as individual mono outputs, stereo pairs, or any combination of the two depending on how you have the Global Audio page LR Bus Indiv. Assign parameters set. When you are asking if they are stereo jacks, are you asking if they are Tip-Ring-Sleeve (TRS)? I've found that some people mistakenly think TRS=Stereo and use the terms interchangeably. In any event, all of the analog audio outputs are balanced meaning that you can use TRS cables to make a balanced connection if you are connecting to a balanced input. If you are using Tip-Sleeve (TS) cable such as an instrument cable, the hum could be due to an unbalanced connection. If you already know all of this, I apologize. I recently had a hum in my setup that I was able to remedy by reading up on balanced and unbalanced connections and then connecting things properly.

marcdeben · Post by **marcdeben** » Sat May 02, 2015 3:40 pm

I am not sure about the balance unbalanced. I am using an instrument cable to go into a powered monitor for the drummer to play along with conga beat. It has no hum through headphones in that output so i'm thinking maybe a ground lifter may work. Will have to try tomorrow at rehearsal. Any other ideas I may try?
Thanks

awyatt1 · Post by **awyatt1** » Sat May 02, 2015 4:03 pm

Instrument cable is TS, so you are definitely not making a balanced connection. If the powered monitor has balanced inputs (you'd have to check the manual), then try using TRS cable. That will give you a balanced connection and it may help. My situation was that I was going from my Kronos (balanced output) to a PA mixer with unbalanced inputs. I had hum with both TS and TRS cable. I had a custom cable made that was TRS on one end and TS on the other. This got rid of the hum for me. First, you'd need to know if the inputs on the powered monitor are balanced or unbalanced.

LZ · Post by LZ » Sat May 02, 2015 5:04 pm

Very likely a ground loop. A DI or ground lift/isolator should do the trick.

Alternatively, you can make sure everything (powered monitor, Kronos, and anything else electrically connected to both of those) is plugged into the same AC circuit, which should also eliminate the ground loop.