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Ground Loop Isolators


Polytrix
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Hi,

 

I've been trying to use a ground loop isolator from Maplin and it's not really removing the interference I get between my laptop when plugged into power, my little dot mk2 tube amp and Scarlett 6i6 USB interface. I like to send audio out and through the tube amp but have to run off battery power to pull it off without high end interference creeping in. Annoying.

 

Anyone have good experience with any particular ground loop isolator for audio use? I think I need a more professional one.

 

 

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I had a feeling (possibly incorrectly) that us UKers didn't have to worry too much with ground looping issues due to our mains supply use of the earth pin. Are the devices plugged into the same power strip, and if so is the power strip of decent quality (or just a £5 jobbie) ?

 

By 'high end interference' do you mean as in high frequencies - If so again probably not a ground loop problem as with that you'll be getting humming ~50Hz with fading harmonics at multiples of the 50Hz fundamental

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Thanks for response. Really appreciated. I just ran a spectrum on it and it is 50hz hum as you describe with falling off harmonics. Even without plugged in power it's still there but at a more steady amplitude so less noticeable. I suppose the higher frequency harmonics are what I'm noticing and not liking most so that's the 'high end' comment.

 

Yeah, they are plugged into the same cheap power strip and I've tried different power outlets (yet to try a more expensive power strip though).

 

 

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Just so I'm thinking of this setup right (and not completely the reverse!) are you doing:

 

[some audio device - mic/instrument ?] -> [dot mk2 tube amp] -> [saffire input (front or rear ?)]

 

Or is this amp being used for the output to your monitors or headphones ?

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The first one Ableton output via Scarlett interface output 3/4 to little dot amp in then back into Scarlett inputs 3/4 on the back on the unit. I just tried it with the crappy isolator in the signal chain on the initial out from the interface and it's still the same interference. Argh! Really annoying, I sent a track through the amp today forgetting about this issue!

 

 

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Not sure if it'll help but have you tried switching from Mic to Inst/Line (or vice versa) on the Saffire Mix Control app for inputs 3&4. Guessing something is unbalanced in the signal somewhere....

 

I've noticed the description for your amp says 'Little Dot MKII greatly increases output impedance' so maybe it needs to be set to the Inst mode and plugged in to the front of the box with 48v turned on (erm, doubly check this first I'd hate you to blow the thing up!)

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Hmmm! I haven't tried the front inputs. All I've tried is the back inputs and left them as is in mix control which I assume is line level. Won't sending it through the front inputs with instrument mode switched on and the 48v turned on simply boost the signal too hot?

 

 

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Really not sure, I'm just thinking that as it has an high impedance output then it needs to be put into a Hi-Z input, which if it's like my Saffire 8i6 is the front two inputs with Hi-Z enabled

 

EDIT: Looks like on the Scarlett one has Hi-Gain support on inputs 3&4 in the Mix Control software so maybe whack those on instead

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Yeah tried changing to high gain for inputs 3/4 and it simply increased the amplitude of the interference. Tried 1/2 on the front with all settings with the same result. Doesn't eliminate the noise just boosts it by going to instrument level. I haven't, however tried the 48v switch. Will that help?

 

 

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plug it all into a 4 way strip, then remove the ground from the plug that goes into the wall. [google this] plug computer and soundcard into the strip. report back

 

 

if that works you have at least found the culprit

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Weirdly adjusting one of the screws (google has helped me) reduces the amplitude of interference on one channel but the ground loop is still there no matter what settings I change. Will try this Fenton cheers.

 

 

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Edit: on second thoughts I don't think I'm confident enough to actually remove the ground cable to test that! I'm not sure if the culprit is the amp, my laptop or the interface. Seeing that it's still present although less when running on battery power makes me think it's the interface or amp itself. Grrr just need to buy a proper isolator I suppose.

 

 

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Edit: on second thoughts I don't think I'm confident enough to actually remove the ground cable to test that! I'm not sure if the culprit is the amp, my laptop or the interface. Seeing that it's still present although less when running on battery power makes me think it's the interface or amp itself. Grrr just need to buy a proper isolator I suppose.

 

 

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iirc you can wrap electrical tape around the ground prong to check too.

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Scarlett has its own power supply yeah. That's always plugged in. I use a USB hub too but that's not powered. I've removed that to see if it impacts and hum remains. I'll try plugging the amp in directly. I bought an isolation box thing too. Will report back

 

 

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I had this problem a couple of times back when I played live, it was easily fixed by plugging everything into an ungrounded power strip.

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i’ve had ground hum problems for years, no way i’ve ever found that fixes it 100%. learn to live with it i say. like, unless you want to build a professional studio from the ground up, with fully isolated wiring and incredibly expensive amps, pre-amps. DI boxes etc then you ain’t never gonna get rid of the hum.

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