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Apogee ONE ground loop question
Old 22nd November 2009
  #1
Here for the gear
 
🎧 10 years
Apogee ONE ground loop question

My question is about why one audio interface has a ground loop issue when another one does not in the exact same setup. Details:

Previously using an Edirol UA-5 as a USB interface. 1/4" outputs in the back connected directly to a pair of powered monitors. Monitors are plugged into a power strip that connects to a different outlet than my computer. No ground loop hum.

Recently tried to replace the UA-5 with an Apogee ONE USB interface. Changing nothing about my configuration other than 1.) plugging the ONE's USB cord into the port where the UA-5 was plugged in and 2.) using a 1/8" stereo to dual RCA cable to connect the ONE directly to the powered monitors. Total hum and high-pitched whine through the monitors.

Leaving the ONE in place, I inserted one of those cheap 3 prong to 2 prong adaptors at the wall outlet for the monitors' power strip. Hum and whine disappeared.

So my question is: what does this tell me about these two interfaces? Which one has the problem? Given that the ONE is more expensive and of supposedly better quality, I would have expected it to be more tolerant of things like ground loops than the UA-5. Or is my understanding wrong? Is there some spec or sensitivity that is desirable but that renders the device susceptible to ground loops that I don't know about?

I don't know if I should be disappointed or not!

Last edited by wrees; 22nd November 2009 at 07:57 PM.. Reason: clarified details
Old 23rd November 2009
  #2
Gear Nut
 
🎧 10 years
Perfectly possible.
I'd try and narrow it down more. Unconnect monitors and try with headphones.

You say one other thing has changed... stereo mini jack to 2 mono RCAs. That could also be the cause. So try without monitors.

Also, not wise to lift the ground at the wall outlet for safety reasons.

I'm in the camp of doing it how Manley/Purple etc treat ground..
(Audio ground and chassis ground on to binding posts on the back.)
This gives people a chance to lift ground or join it at one chassis point in the rack full of gear.
Old 23rd November 2009 | Show parent
  #3
Here for the gear
 
🎧 10 years
Neither device has hum with headphones.

I tried several different ways of hooking up the speakers: a Monster 1/8" stereo to dual RCA cable, a similar cable from Hosa, and a Hosa 1/8" stereo to dual 1/4" with two 1/4" Monster patch cables. All had hum that went away when I used the 3-2 prong adaptor.

I will try two more things today and report back:

1.) I'll plug the power strip that powers the monitors into the power strip that powers the computer.

2.) I'll plug one of those power outlet testers that has an led for ground into the power strip that powers the monitors and see what it says when I insert the 2-3 prong adaptor.
Old 23rd November 2009 | Show parent
  #4
Here for the gear
 
🎧 10 years
1. When I use the 2-3 prong adaptor on the the power strip that powers the monitors and connect the monitors to the ONE, the power outlet tester plugged into the strip shows a "correct" connection, which means it is grounded correctly.

2. When I use the 2-3 prong adaptor on the the power strip that powers the monitors and do NOT connect the monitors to the ONE, the power outlet tester plugged into the strip shows an ungrounded connection.

To my understanding, that's a lot of evidence that the monitors are being grounded through the ONE. Anything else I should try?

Strangely (to my understanding), when I plug the power strip that powers the monitors into the power strip that powers the computer, I get all the hum and whine again. In addition I get a mid-range-y constant chatter, almost like a fan noise. If I use the 2 to 3 prong adaptor to connect the monitor power strip into the computer power strip, the hum and whine go away, but the mid-range chatter stays. I had thought the hum and whine would not have happened since I think there was only one path to ground. Any thoughts about that?

Last edited by wrees; 23rd November 2009 at 07:35 PM.. Reason: clarified
Old 25th November 2009 | Show parent
  #5
Here for the gear
 
🎧 10 years
One thing I did figure out was that my monitors automatically amplify the signal coming in through the RCA connections a lot more than the signal coming through the 1/4" connection. What this means is that the hum and whine were low enough at the 1/4" connection that I could turn the monitors' attenuations down to like -20db and the hum and whine would be low enough not to be heard. If I then crank the output level on the ONE I can get a decently loud signal with no hum or whine. The hum and whine are are not affected by the output level on the ONE, so cranked all the way, I get a usable signal to noise ratio. Well, usable for near-field monitoring, anyway.

Of course, if I have the output cranked for the monitors, I've got to be careful when I switch to headphones!

Also, now looking at potential alternatives to the ONE. This is just a bit to convoluted.
Old 22nd December 2009 | Show parent
  #6
Gear Head
 
Sad Iron Studio's Avatar
 
🎧 15 years
I'm having the same problem. I even had Apogee send me a different unit and still a low level whine. I don't have my monitors running directly from the One; everything's running through a Big Knob. Lifting the ground of stuff makes me nervous, but maybe I'm being ignorant. Without unplugging everything in my studio, how can I figure out how to get rid of this problem. I really like the One and would like to use the convertors when i don't need all the inputs of my 828mkII, but the whine is making it almost a non-starter
Old 4th January 2010 | Show parent
  #7
Gear Head
 
🎧 15 years
Quote:
Originally Posted by jasonlewis ➑️
I'm having the same problem. I even had Apogee send me a different unit and still a low level whine. I don't have my monitors running directly from the One; everything's running through a Big Knob. Lifting the ground of stuff makes me nervous, but maybe I'm being ignorant. Without unplugging everything in my studio, how can I figure out how to get rid of this problem. I really like the One and would like to use the convertors when i don't need all the inputs of my 828mkII, but the whine is making it almost a non-starter
Having read his thread, I must say that I am extremely disappointed with the ONE. IT is nigh on useless unless you can hook it up to your monitors as Apogee claim. I bet you any money there is no single way to eliminate this hum as I have tried ad nauseum. I have invested in some very good equipment and have never had any grounding issues until the ONE. I would like Apogee to tell us the truth. That if you hook the ONE up to powered monitors you will invariably get some some hum, irregardless of how careful you may be.
Seriously this is driving me crazy. Such a great piece of equipment flawed by this issue.

A postscript: I attached the ONE outputs to a couple of XLR adapters through a volume controller to the speakers without hum. Go figure. I have left the setup as I have tried this before with no success. Obviously, something is off that was creating the interference. ???

Problem is the volume is not optimal through this system. I have been contacted by Apogee Techs advising that I use a ground lift adapter. Anyone had any experience with them?

Where do you get these 2 to 3 prong ground lifting adapters. I have tried everywhere here in Melbourne but no one seems to have them and in one case I was advised against them because of the 240volt power we have here.
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