FAQ: High Frequency Noise on Auxes

[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!!

[RoadRanger]

If you lose track of where someone's posts are you can click on their name and choose "Show Posts" over on the left. BlendedMix's post can be found here:
http://cacophony.aspinock.com/index.php?action=profile;area=showposts;u=4412
I didn't delete any of his that I remember?
I do move posts into FAQ's so folks can find answers to their questions without folks asking the same questions over-and-over like on most forums (Kudos to Mike Rivers for that suggestion). Looking at the number of folks who just stop by to lurk here vs those that post would indicate I could increase the message volume here 10x by eliminating the FAQ list but the goal here is to help folks out, not stoke our own personal egos I think? Perhaps if that's your goal also you'll post a link to the actual supply you are using? Thanks!

[robbocurry]

Maybe a link to said power supply on Amazon?

+1 plz

[RoadRanger]

At the least I'm sure most of us would like a cheap spare PS to carry in case we misplace the original or it goes teats up on us at a gig . I'd rather buy one that someone else has already tested rather than play "guinea pig" with a new one .

If folks do want to run a safety ground I'd suggest running it to the chassis of one of the grounded devices in your rack. If your DL1608 doesn't live in a rack a short pigtail at the DL1608 with a spade lug to male faston would let you easily disconnect it from the ground wire. None of that is Kosher of course. The "right" solution as I posted earlier is to have designed the DL1608 to take a three contact power plug so a separate ground could be used. I believe I have a Behringer mixer or two that do this - guess Mackie should have copied them .

[WK154]

The reason I haven't posted a link should have been clear, I was dissatisfied with the Amazon purchase. I like to get what I order don't you? As far as it not being "kosher" is clearly incorrect. Since the DL1608 that we all have is not going to be changed by Mackie gratis this is a solution for those that want to lower the noise. I thought the purpose of going with the DL was to eliminate the rack? Parts of the BlendeMix posts are missing. I'm also not finished with my investigation for a recommendation.

[RoadRanger]

The reason I haven't posted a link should have been clear, I was dissatisfied with the Amazon purchase. I like to get what I order don't you? [...]I'm also not finished with my investigation for a recommendation.

Cool, please let us know which one you settle on. Personally I'd rather have the one you received than a two wire.

I still have an amp rack for subs and monitors so running the ground wire to that rack would make sense to me, YMMV . OTOH I'm not having the "problem" so...

I may have "split" one of BlendedMix's posts between two threads if half of it applied to a FAQ and half was about something else. I also sometimes go through and "split out" stuff posted in (or moved to) the FAQ threads that isn't directly relevant. Didn't mean to freak you out .

[WK154]

Splitting makes things hard to find. As to the Amazon PWS I'm not sure you'd get the same one if you order so hold your horses. Sound like I'm announcing the release of V1.5. Going to the LA Opera, Bye.