[RFI] Hum in Bose QC2 headphones

[David Jordan]

What fun...take a close look at the jack.  Some are steel with chrome
coating...the two metals start to react and a resistance between the chrome
and the steel develops increasing the impedance...not good if this happens
on the ground ring.

Also, is the connect cable three wire unshielded or stereo pair each
shielded or another variation.  Radio Shack was famous for selling audio
cables that that appeared to be shielded cable but were simply three wire
unshielded.  

Appears when you use the headphones on a pure DC battery source you have no
problems.  When you use them on a DC power supply source you get hum.

The fella that mentioned EMF induced hummm might be on to something. PC
monitors and ham radio power supplies are known sources of EMF clouds that
can reach out from a few inches to a couple feet away from the source.

Have fun chasing this one down.

Best,
dave

-----Original Message-----
From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
Behalf Of Gary Smith
Sent: Wednesday, January 14, 2009 4:22 PM
To: Rfi at contesting.com
Subject: Re: [RFI] Hum in Bose QC2 headphones


> If the headsphones have a ground problem the issue might be reproducible
on
> another piece of equipment (PC, stereo, walkman, etc.).
> 
> 73,
> Dave
> Wa3gin

This is most interesting (& it would be more interesting yet if the 
hum were not an irritation).

The cord to the headset seems to be likely involved, at least that's 
what I'm leaning towards.

If I have no cord attached (it is a removable plug) there has never 
been an issue. Since the headphones use a battery & other than 
getting a K3, I'm cheap... so the headphones have only been used to 
quiet down noisy environments like lawn mowing, next to an engine & 
so on. The only times I recall using it with music was with my Sansa 
MP3 player and I never had an issue with it there.

So to deal with if it's happening otherwise; 

* I just plugged it into my battery powered Sansa player and there is 
zero hum. 


* I now plugged it into my laptop while attached to the laptop PS and 
there is a definite hum.
- Disconnecting the PS cord and the right sided hum is far worse.
- Touching the monitor jack (the only bare metal available) and the 
hum goes away.


* Plugging it into the K3 and the hum is present.


* Disconnecting from everything with the overhead flourescents on and 
there is a slight hum.
- If I touch the metal be it tip, ring or shaft the slight hum goes 
away.


* touching the bare tip, ring and shaft to anything grounded in the 
shack causes the hum.
- But when plugged into the K3, my touching anything metal makes the 
sound go away. But there's nothing of me touching anything conductive 
on the headphones.

And... going back to the laptop; with the laptop plugged in to it's 
PS and with the QC2 plugged into the laptop, touching metal (like the 
metal on my paddles) will stop the hum. Unplugged and the hum worsens 
but touching metal other than the metal on the video put jack does 
nothing.

Most interesting...  

#$%^&

Gary
KA1J

Interesting the Sansa MP3 player has zero issues with the QC2 but the 
radio and laptop do.
 
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