Resolving 60 Cycle Hum From Avantone Mixcube

C

cyberdaniel82

New member
Hi! I’m hoping to receive a suggestion or two for chasing down and/or mitigating 60-cycle hum in my signal chain.

I have a Belkin power strip plugged into a grounded outlet. All of my gear - including my rack - plugs into the Belkin. My rack includes a power conditioner and an RME UFX+ interface.

I purchased a single active Avantone MixCube for mixing in mono. The MixCube receives signal from a verified good TRS cable connected to the RME UFX+. No matter what outlet I use to plug in the MixCube’s power supply (Power strip, Power conditioner, or two different wall outlets), I get some 60-cycle hum out of my two main monitors. (If I flip the ground switch on the MixCube, I get major hum out of only the MixCube). I’ve confirmed that a) it’s a 60 cycle hum, not 120, b) the hum goes away if I put a ground lift on the MixCube’s power plug, and c) the hum goes away if I disconnect the TRS connection between my RME UFX+ and the MixCube. I’ve included a crude visual diagram and a picture of my space (the cables are not usually as haphazard).

A two-pronged ground lift fixes the problem, but… my understanding is that leaving a two-pronged ground lift in place is a poor/dangerous long-term practice. I’ve seen products like the Ebtech Hum-X which seem like perhaps they’d constitute a solution. I figured I’d ask the forum for advice before going that route, though. Any advice would be greatly appreciated!

- Daniel

60cyclehum.jpgIMG_8948.JPG
 
All good advice thus far, especially that of NOT lifting mains earths!!

Lifting signal grounds, shields, is probably the best way to go because it has no impact on audio quality. Transformers, even very expensive one can and can also PICKUP hum!

One caveat about lifting screens, in rare circumstances this can leave the gear prey to RFI, radio breakthrough. This can usually be fixed by linking the screen back to the jack sleeve (or XLR pin 1) with a low value capacitor. 1nF/1000 pico Farads is ideal. You can get very wee, low voltage ceramic capacitors that will fit inside a jack plug. BUT! If you modify cables in this way BE SURE to label them!

Ground loops are often associated with laptops, their chargers to be specific because they invariably use a the 'clover leaf' 3 pole connector. Last year I found a high quality, 90 watt 'universal' charger made by Duracell and that uses the earth free 'fig 8' two pole mains input.

Dave.
 
Thanks, guys! It's a complicated topic and I only grasp some of the rudiments. I do build my own cables, though. With TRS cables, I twist the braided metal shielding and solder it to pin 1 on each TRS connector. Regarding the TRS cable which connects my interface to the Mixcube: are you saying that I could disconnect the shielding from pin 1 on one side of the TRS cable (connecting it to a tiny capacitor instead) to break the ground loop? Or am I completely misinterpreting the suggestion? Thanks again! - Daniel
 
cyberdaniel82 said:
Thanks, guys! It's a complicated topic and I only grasp some of the rudiments. I do build my own cables, though. With TRS cables, I twist the braided metal shielding and solder it to pin 1 on each TRS connector. Regarding the TRS cable which connects my interface to the Mixcube: are you saying that I could disconnect the shielding from pin 1 on one side of the TRS cable (connecting it to a tiny capacitor instead) to break the ground loop? Or am I completely misinterpreting the suggestion? Thanks again! - Daniel
Click to expand...

Yes. Best to start afresh, cut the shield back to leave just ' hot' and 'cold' cores. I like to fit 20mm or so of heat shrink sleeve over the end to 'capture' any shield whiskers. I would not worry about the RF 'tie down' capacitor at this stage, it is quite a faff to do inside a jack plug body and you are unlikely to have any suitably wee capacitors to hand.

N.B. You only diss' the shield at ONE end of the cable and if RF breakthrough does occur, try flipping it around. Note also that if using this dodge to two monitors, both cables need to be treated.

I have to go and stand in the supermarket Q for the wrinklies (I am 74) soon but I can do you a diagram* later if you like?

*I have posted such a drawing here in the past but do not have the LEAST 'king clue how to find it! Mods??

Dave.
 
If lifting the audio ground fixes it then it's sorted. Until you change configuration with a new purchase. Worth keeping in mind that grounds on balanced connections don't actually do much. Safety grounds are for one job, audio grounds are doing a different job. No need for the capacitor, current flow in ground for audio isn't needed or wanted.
 
rob aylestone said:
If lifting the audio ground fixes it then it's sorted. Until you change configuration with a new purchase. Worth keeping in mind that grounds on balanced connections don't actually do much. Safety grounds are for one job, audio grounds are doing a different job. No need for the capacitor, current flow in ground for audio isn't needed or wanted.
Click to expand...

Agreed, "no need for the capacitor" 98% of the time but the ONE thing the shield does is keep RF out of audio circuits and that function relies on a low impedance path to ground for the screen.

Living just a score or so of clicks from both Rugby and Daventry I spent much of my early 'electronic' life keeping RFI out of punters gear!

Simms-Watts amps were the WORST!

Dave.
 
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