Monitor mix output of Qu-16 into HM-800 very noisy

Question

I recently acquired an HM-800 in order to provide my fellow musicians with their own in-ear monitor mix, as my Qu-16 is capable of outputting four different mono mixes. Sadly I noticed that the output of the HM-800 is very noisy to the point of it being unusable for its intended purpose.

I created an image to better describe my situation. A1 is the output port of mix 1. A2 is the headphone monitor output of the mixer. M1 is the input of the HM-800 unit. Y1 is the input of an AG06 USB mixer which I used to check if the output of the Qu-16 itself is noisy:

I used a Cordial CFM 1,5 FV XLR 3-pol female to TRS male cable to initially connect A1 with M1, which resulted in a very noisy signal. I tried using a second cable of the same type with the same result. I then connected A1 to Y1 using the very same cable in order to check if the mixer itself produced noisy output. The resulting signal was completely fine, almost noiseless even. I then tried to connect the headphone output A2 to M1 using a Cordial CFM 1,5 VV TRS male to TRS male cable. This output was once again completely useable, but the mixer only provides a single TRS output.

I would like to ask for help regarding how to solve this issue. I note that I contacted Mackie support before as I suspected faulty product. I have since tested another unit with an entirely different serial number with the same result. Support stated that the mixer could be outputting at MIC level, when it should be outputting at LINE level, but I found no way of adjusting the output level of my mixes. If there is a way of adjusting the volume please tell me how to. Furthermore, the AG06 receives the exact same signal and is capable of producing a clean signal.

Could it be that I am using the wrong type of cable since the setup seems to work fine when connecting it to the headhpone output A2?

I am thankful for any kind of information as I am relatively inexperienced when it comes to audio routing!

Answer 1

Using the help of Mike C in this thread of the Allen & Heath forum I figured out a solution which I will repost here:

I tested a few different cables and suddenly the output was very clear, even with the original cables. Properly plugging everything afterwards resulted in noisy output again though, which is why I tried to plug the cables only half way in, which seemed to completely resolve my issues. I suppose this acts in a similar way as modifying them in the way you described. Furthermore, since the Mackie allows for setting an input to mono I don’t have issues with only one channel of my IEMs being fed.

It may not be a very clean solution but it works perfectly fine!