help USB hum

[One and a half]

ack....i didnt even think about it being something else plugged into outlet as computer is on....geesh, i can't discounnect everything...there must be 20 things plugged in....it's kind of my "office corner", 3 computers, 2 printers, monitors, phone, magicjack, lights, tons of stuff....yea, that's prob the problem...not the computer or ac in? something else causing the noise? yea, i don't want to try and figure that out...but for peace of mind, ii agree, i will run extension cable.

 

question...if i run extension cable to my pc and no more hum, is it still possible that something is wrong (ground with amp?) or i can rule that out, and rest in peace that there is no problems with my amp. that is my main concern since i just spent $600 on repairs of this $2500 amp.

 

going to go run an extension cable now....

 

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.

 

Here's a valuable resource on ground loops, it's not so simple to solve.

[One and a half]

this is the first time i am using with this amp. i didnt have the hum from the previous amp, but as "one and a half" pointed out the denon only has a 2 prong receptacle.

 

it pretty much is down to the simplest. with the 3rd prong used from the receptacle, it hums. without the 3rd prong, it doesn't hum. i just don't know if that means the problem is with the amp or with the house wiring.

 

short of trying another ma6500 amp, i don't know how to tell what is the problem...the house wiring or the amp.

 

Neither the Mac amp or the house wiring is to blame. It's the interaction of wiring, the amp and the computer system that causes the problem. Yes, everything is supposed to work together, but in the real world it doesn't.

 

Here's a link that shows how a ground loop is formed. They usually appear somewhere else completely perhaps through a printer, or wall wart not even remotely used with the amp.

 

Finding the cause is to analyse the whole setup from the receptacle forward including to check how good the grounding system is in your house to begin with.

 

Systematically figuring out the paths of the signal wires, comparing them to the ground connected equipment, and even sometimes taking measurements. It's not simple, and without any drawings of what you have connected, these pages can go on for some time and by the end of it, we'll be shouting at each other, since this is a word only forum and not an interactive process. We need photos, drawings, voltage measurements, types of cables used to test the shield integrity, routing methods, proximity to other AC lines, SMPS, the list goes on.

 

We *could* try, but without all that above, we have no place to start. Pro help is available of course, get your electrician to check the receptacles first off. If you can find a control or instrumentation company, they could help you in finding the culprit.

[One and a half]

above you stated the mcintosh isn't the problem.

 

is it "possible" that the mcintosh is the problem? isn't it possible that there is a bad ground, loose wire, or something else internal to the amp that is causing the ground loop?

 

that really is my only concern.... i can go back to using the denon in this room, and then use a vivopc (mini pc with only 2 prong ac) with the macintosh in another room.

 

i just want to be certain there is no problem with the macintosh itself.

 

From Post #11:

If there's nothing connected to the amp on the inputs and it still hums, then the repair is ineffective.

 

By which I mean nothing connected on the inputs, they are all disconnected. The only thing connected are the speakers and the power cable, nothing else.