help USB hum

[beerandmusic]

driving me nuts....

 

i keep getting hum out my usb port...it seems if i wiggle the cable the hum will get quieter and louder, but cant get it to go away.

tried different cables, different usb ports...

 

for testing using pc out to dragonfly to cable to amp

 

check this out...

 

if i play my android phone connected to the amp, no hum.

play the same phone, same connection, but hook the usb cable to my phone from my computer (like to charge it), the hum returns.

 

i even tried 3 different computers

the two different desktops both caused hum

the laptop running on battery, no hum

 

what up???

[beerandmusic]

thanks for the suggestion..i just now tried your suggestion...no difference.

 

i dont mind putting the "cheater plug" on my pc end, but don't want to put it on my amp end. i just got the amp back from repair, maybe it is at the amp end...the repair tech (mcintosh authorized), said he had no hum issues when he tested it....it's a $2500 amp and $600 repair bill so i do want to know for sure there is no problem with the amp...i didnt seem to have the problem with my denon reciever....but the amp does sounds great under other scenarios e.g. cd (albeit the cd was powered from same outlet as amp), tablet or android (as long as no usb connection), and laptop usb port (running from battery, never tested with power connected).

 

problem does seem to be desktop usb which is on different outlet.. but even when i ran a power striip from same outlet as amp to my pc, i still get the hum.....

 

this has been driving me nuts for 6hrs already! I don't want to give the mcintosh my blessing as 100% until i can figure this issue out.

[beerandmusic]

ok, so i grabbed a 4th pc (a portable vivopc), plugged into same outlet as amp, and when i connect the usb cable to the tablet, NO HUM.

 

so now the question is, what the f is this ground loop and what do i need to do to fix it?

 

my main pc (that i want to use) is too far from the amp to plug in same outlet, and don't want to run an extension cord ....

 

i guess i could buy an external dac and plug the dac into same outlet as amp and that should solve it? but maybe not? would rather know how to fix this ground problem if thats what it is....

 

also still curious why i didnt have this problem when i used a denon reciever instead of this repaired mcintosh amp.

[beerandmusic]

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....

[beerandmusic]

ACK!!

 

so i ran an extension cable from same outlet as amp, and still had hum...an interesting new development though...when i ran the ext cable to the pc, now my monitor has a wave thorugh it????!! ACK, UGHGH...!!!

 

so now i think the problem is something from the amp end?

 

the troubleshoooting continues....

[beerandmusic]

I had this same issue, and I was not about to put all that computer digital garbage onto the same circuit as my analog system. A usb/spdif (toslink) converter solved my issue.

 

this $2500 amp only has analog inputs and data ports (whatever those are)...no spdif

[beerandmusic]

at this point i am more concerned on what the problem is and how to fix it, rather than a bandage.

 

i want to know if the problem is with my old 1959 house wiring or the amp, since i just got it and paid $600 in repairs by authorized mcintosh repair servicer.

[beerandmusic]

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.

 

thanks for all the info. i have found a short term resolution..., but more importantly is i want to know what the problem is..... is my problem the 1959 house wiring or some ground problem internal to the amp.

 

the short term resolution seems to remove the ground on the amp end (removing from the computer end didnt fix it).

so i am using one of those cheater adapters that removes the 3rd round ground plug from the stereo.

 

the issue therefore is whenever a ground from the receptacle to the amp is in place, i get the hum. if i remove the ground from the receptacle, the hum goes away.

 

1. so is the problem with my house wiring or open ground in the amp and how do i determine?

2. also, can this be bad or damage the amp by using one of these cheater plugs?

 

[beerandmusic]

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.

[beerandmusic]

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.

[beerandmusic]

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....

[beerandmusic]

And blutooth off as well.

 

Sent from my SM-T113 using Tapatalk

 

 

not applicable...got same hum using dac from usb port and pc with no wifi.