Unofficial Mackie User Forums > DL1608/DL806/DL32R/ProDX Mixers

FAQ: High Frequency Noise on Auxes

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TimC:
I'm happy to report back that the Radial Pro D2 cleaned up all the noise (high frequency and hum) that was getting into the DL1608 from my Motif XS8 synth.  The best results required using the pin 1 ground lift feature the Radial box provides.  It's constructed like a tank and gets the job done  :)

Greg C.:
Nice! Glad to hear it.

WK154:
Having read all the guesses and theories about what causes the hum and high pitched noise on Aux's I decided to go back to basics which this mixer seems to lack. From Aliens to RF to cables etc. the guessers of "it's the power supply" pat your self's on the back. The obvious problem is the power supply all $3.99 worth of it. Mackie's new innovation after Greg  and I'll coin the word "Bean Counter Engineering" is in full bloom. Onyx mixer are notorious for their power supply problems as is now the DL. Fortunately there is a simple solution.

For $9.00 and $8.00 shipping and handling from Amazon you too can be rid of the noise issues on all unbalanced lines. The problem stems from a pass thru of the safety ground to the power supply ground. This imparts a power supply generated ripple onto the shield and pin one connections to the tune of 450uV or -65 dBu (its actually chassis ground current in uA but my measuring setup measures uV ). It's also distorted accounting for the higher pitch sound along with hum. The general opinion for tolerable noise levels is -80 dBu or less (~80uV). This cannot be achieved with the current supply even with the additional chassis to safety ground wire that is also needed to get below -80dBu. In defense of the manufacturer APX, they do have the correct non pass thru supply if Mackie would only order it. Back to the solution.

The supply I ordered 6 amp max @ 12V isolates the power supply ground from safety ground (CE approved). Murphy of course was in the picture. I ordered a two prong plug supply as pictured and received a three prong version instead. It did however isolate safety ground from signal ground. I would have preferred the two prong variety since it would also have given me the added protection from miss-wired AC outlets. Yes they do exist along with poor or non-existing safety grounds in the real world. I always carry a Multimeter with me on a new environment for just that reason.

The needed chassis ground to safety ground wire (I used 16ga wire 14 or 12 would be better) was attached above the power supply plug with a spade lug. Loosen the two screws and place the spade lug between the plastic and the main body. There is a chassis ground flashing behind the plastic. Re tighten the screws and run the wire to the safety ground the mixer supply is plugged into. This configuration gave me 20 - 30uV ( -92 to -88dBu) without the ground wire you would get 350uV. You will never eliminate the noise but you will make it irrelevant in the system. This beats spending $60-$70 per Aux on a DI box.

One word about safety ground. If the ground is noisy or non-existent you will still have problems the severity of which I can't predict. There will also be poor designs that will impart noise on the mixer and for those you will most likely need a DI box. Most well designed kit will be fine. My test setup was a Behringer C50 self powered speaker using the RCA input driven from Aux3. Definitely unbalanced and yes I could hear the Hum and high pitched noise with the Mackie supply. For giggles I also ran a 50 foot cable from the mixer to the speaker with no additional noise  (coiled and thrown on top of my AC cables). Other environments may not be so kind. I will get my lab supply next week for low noise power and will see that the poor safety/chassis ground are the cause behind all the noise. I'm also near the lower limit of my meter (10uV).

RoadRanger:
Maybe a link to said power supply on Amazon? :)

WK154:
RR: How about leaving my posts where I put them!!! It's not about high frequency noise on aux's it's about the power and grounding system of the DL. Also restore the post from BlendedMix since that is far from over and the information in that post would have been very useful. It's starting to feel like the Mackie forum!!

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