help USB hum

[AlainGr]

Would it be possible for you to bring your PC, dac and amp at the repair shop ? Or to a friend's place near you ? I know it is not practical, but... I know what you are into, I have had my share of ground loops. When I had one, getting rid of it was a game of patience. Putting a cheater to one component, then the other, etc... And when I thought the problem was solved (in my situation, lifting the earth on the amplifier), then a second ground loop appeared at the subs level... What a mess

[AlainGr]

Hi Beerandmusic.

 

You are right. Before investing in other components, it would be a good thing to pinpoint the culprit for the ground loop (if it is a ground loop). If you run an extension just for the sake of your search, maybe it will bring some answers ?

 

At some point, what I did was this to narrow the identification of the problem:

- I detach all AC cables from components that have no direct relation with the sound system (if they are plugged in the same wall AC) and also the interconnects.

- I disconnected the subs also (AC and interconnects).

- I got as many cheaters as there were components. All individually. Do not do this on the main connection of a powerbar, as the grounds are generally all tied together on the same rail inside the powerbar...

- Once I have the minimum components required to play music, I disconnect, starting from the PC, up to the power amp (or the receiver).

- If you have a power conditionner, do not forget to remove it also (just in case)

 

And when nothing seemd to point to any of the components, here is the extreme...

- I shut all the breakers in the house, except for the ones that require power for the sound system.

 

Yeah, I know, there is not a lot of fun in doing this, but the less components you have to check, the easier it gets to identify the potential source of the problem. This will not necessarily explain why it is happening, but as least you will maybe have a starting element of the answer...

 

To tell you: I never was able to solve my subs ground loop problem. When I find the solution for them, another gournd loop reappers !!!! I have put that aside for the moment, after trying an isolator for the subs (that did not work)...

 

But please - if you decide to try all of these - my word of wisdom is this: ensure that each time you manipulate any cable (AC, interconnect, usb), you turn OFF the volume and the power of each component. Not doing so may bring costly problems... And if a component has its earth lifted, be very careful... There can be a lot of current in these boxes - a lot more than you would expect...

 

Regards,

[AlainGr]

Mmmm... I can tell I swore a lot when I did my investigation a couple of years ago. It's not for nothing that I dropped the prolem with the subs maybe it would be simpler for you to move the few components you wish to test in another room ? Not knowing how your are set, you can look for the simplest way to arrange this. Instead of disconnecting all (and I undersant this too), you could move yoru power amp, PC and speakers (I don't know if they are easy to move) in another room, on a different circuit...

 

I always try to get to the simplest solution... I am lazy

 

But remember for the sake of all the trouble it brings... Ensure that you have your system alone on a circuit, to narrow your search. Using cheaters and removing them one by one will help, but take notes

 

Boy, would I like to be able to make diagnostics from distance... But I can't. I am not saying you will find the solution in a few minutes. If it still does not help, to bring the components (or to invite the technician to come by)... Maybe one day it will be possible for one to appear in 3D and see all around what is going on...

 

Hey, hope this helps, but I feel the pain also... Do not get discouraged... Time and patience, even if it is very frustrating.

 

Just before I leave for the night: was this happening before you had your component repaired ? Has something changed in between ?

 

Regards,

[AlainGr]

Oops... Yes, there seems to be something odd happening... Could it be the electrical wall plate that has a problem ? Have you checked if there is a buzz at the electrical board (breaker) ? Sometimes things can get serious...

 

Have to leave for the night (work tomorrow)... If it gets overwhelming, maybe a technician or an electrician ?

 

But over all, be cautious ok ?

 

Regards,

[AlainGr]

The Denon and many other HT receivers have a 2 prong IEC inlet, requiring no ground connection. The Macintosh amp would have a three prong inlet. If it plays ok other than the Dragonfly, the amp repair is OK. If there's nothing connected to the amp on the inputs and it still hums, then the repair is ineffective.

 

Since in a Hifi system, the amplifier is the conduit where all sound is controlled, it is the most logical place for a common ground to exist. When you connect the computer (and all the other gear), the path to ground must be a hell of a lot better with the Mac amp than the rest of the equipment, so all the hum goes through the amp connected by the interconnects from the source.

 

When you connect an iPhone, or the portable computer, their inputs float to ground, so there's not a problem.

 

A fix? Two choices

 

1.By the time you spend money on extenders, and the like, suggest to buy a small PC (like a mac mini/Nuc) plays music only, that uses a 2 prong power source and remote VNC with your LAN, and have the Dragonfly plug directly into the Macintosh with a short 3.5mm to RCA cable.

 

2. Buy an isolator from Jensen Transformers, it blocks the hum, but passes audio. CI-2Mini might just do the trick.

 

 

If was hoping your would come by

[AlainGr]

Hi again Beerandmusic,

 

Do you recall having that problem before you brought your power amp for repair ? Did you do something in between, like moving a few components on the same circuit ?

Does it also hum if you put it on a circuit where it is alone ?

 

As you have guessed, it is a matter of eliminating and narrowing the problem to its simplest.

 

If it still hums and it was not doing that before, maybe you should bring it to your technician ? I suppose he gives something like 30 days warranty or else ?

 

At least you will have the peace of mind if the problem is fixed for good...

 

Regards,

[AlainGr]

ok, i moved the entire configuration that hummed, same cables, amp, source to another outlet (my main listening room which is on power conditioner), and NO HUM. YAY!!! i don't have to carry the heavy beast back to repair.

 

thanks for all the help everyone.

 

now i have to start another thread...."what makes a bigger difference, the dac or the amp"...i am surprised by my new opinion....

I am very happy that things have settled