[RFI] Headphone Hum

donovanf at starpower.net donovanf at starpower.net
Tue Dec 10 10:23:32 EST 2013


This definitely is an off topic post, but its such a common and easily solved problem that its worthy of a reply. 

The Pyle PHE300 2-Channel Hum/Noise Destroyer is an inexpensive and extremely effective solution 
to sound card related hum and noise problems, its almost a silver bullet. 

Its I/O jacks are 1/4" stereo, so you'll need adapters. 


The Pyle PHE300 so inexpensive it isn't worth the time and effort to build your own transformer isolation box. 
A Google search will discover many suppliers at prices of $15 to $20 including shipping, for example: 


You should be aware that almost all off-the-shelf audio cables are N O T shielded. 
In most cases it doesn't matter, but in some cases it does. 
A Google search will discover suppliers of inexpensive shielded audio cables . 


----- Original Message -----

From: Bob at N2SCJ.net 
To: Gary at ka1j.com, rfi at contesting.com 
Sent: Tuesday, December 10, 2013 1:08:25 PM 
Subject: Re: [RFI] Headphone Hum 

Is this a 60 cycle hum? Perhaps run some braided ground wire from the 
computer case and the K3 to your single point ground? 


-----Original Message----- 
From: Gary Smith 
Sent: Tuesday, December 10, 2013 5:36 AM 
To: rfi at contesting.com 
Subject: [RFI] Headphone Hum 


I've got a problem I just discovered and whilst its not RFI to my 
radio, this forum is likely a good source for a resolution. The 
problem is hum in my headphones. I've switched headphones and 
verified the hum is present in both my noise cancelling Bose QC-15 
and a standard cheap headset that collects dust. The QC-15 are far 
better headphones and the hum is louder in the Bose. 

Here's how things unveiled and all the details I can offer; I use a 
creative E-MU 0404 USB sound card to do recording work and to play 
music from my computer. I have two self powered Mackie HR824 studio 
monitors connected to the outputs of the sound card. The "card" is a 
self contained device with controls which sits on the desk next to my 
K3. When I plug the headsets into the sound card headphone out there 
is no hum. When I plug the headsets into the K3 there is no hum. 

The K3 is connected to the computer via a RS-232 cable to a RS-232 
PCI card. The sound card is connected via a metal shielded USB cable 
with included ferrite shield next to the computer connection. 

Normally I wouldn't want to listen to sound from the computer while 
listening on the K3 but I've found a reason to use the sound card and 
the K3 simultaneously and that is my Logic 9 logging software and 
when a needed spot for DXCC on CW comes through, I have it set to 
announce that alert. Rather than leave the self powered speakers on 
all the time I figured I'll turn them off, put a stereo Y cable from 
the sound card to the front phones connection on the K3 and then use 
the open female from the Y to connect the headset to. This way when 
the alert is announced I can hear it while listening to the K3. There 
is no other reason to listen to both the sound card & K3 at the same 
time and this sounded like a simple solution. 

The problem is a hum generated when I interconnect the sound card & 
K3, it' a constant low hum and it does not increase/decrease by any 
change in volume from the sound card or K3. I re-checked my grounding 
& found no apparent issues, jumpers between bits made no change. I 
started unplugging everything connected in the shack and the sound 
continues until I unplug the USB cable from the sound card to the 
computer and the hum stops. I killed the power to everything and I 
still hear the hum in the QC-15 headphones, removing the USB cable 
from the computer while all the power is off resolves the hum. 

So I'm on the floor in the basement (carpet with cement underneath) 
trying to unplug things to see if that makes a change and I noticed 
the hum varied in intensity as I moved about. Working with this I 
found if I bring my head next to the floor the hum completely stops 
and when I pull up the hum increases. With the power off I did not 
try this with the non-powered headset but with the computer running I 
did try it and I get the same stoppage of hum when the standard 
headphones are near the floor. I re-verified it with the QC-15s and 
though the hum is markedly louder in the QC-15s, when I put my head 
next to the floor the hum goes completely away. Apparently when the 
headphones are next to true ground the problem resolves. 

Any suggestions on what might be happening and a straight forward way 
to resolve it? As it is, I'm leaving the powered speakers on so I can 
hear an alert when it's sent and just plugging straight into the K3 
with the headsets. sticking my head in the sand might actually work 
in this case... 

Thanks for any thoughts on the matter. 



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