[mythtv-users] Slightly OT: receiver input buzzing/humming

Steve Briggs zzybaloobah at yahoo.com
Wed Jan 11 06:18:00 UTC 2006


I've had similar problems, particularly when the
2 devices are plugged into different outlets.
The problem is due to slight differences in the
ground potential at the 2 units, which results in 
ground currents flowing down the shield on the audio
cable... which ends up as 60 Hz hum.

What generally works to reduce the noise is to get
a good heavy piece of wire (say #12 stranded or better)
and screw it to both the chassis of the myth box and
the stereo reciever.  This provides a lower impedance 
path and gets the currents off the cable shield.

Steve


> > From: matthew.garman at gmail.com
> To: MythTV Users List <mythtv-users at mythtv.org>
> Date: Tue, 10 Jan 2006 20:22:59 -0600
> Subject: [mythtv-users] Slightly OT: receiver input buzzing/humming
> 
> 
> I've got a Yamaha HTR-5550 receiver that receives input from (among
> other places) my mythtv box. This is an analog input: the cord is a
> male 1/8" stereo plug (PC side) that splits into two RCA connectors
> (amp side).  The motherboard is the Chaintech 7NIF2.
> 
> Recently, I've noticed that when I'm not playing music or watching
> TV (i.e. silence), there is a distinct buzzing/humming sound coming
> from the speakers. The sound is barely noticeable at the "-40.0"
> volume setting, and quite pronounced by "-30.0".
> 
> I've tried messing with the volume levels on the PC; it does not
> make a difference in the buzzing. I've tried re-seating both ends of
> the cord (to no avail).
> 
> Note that when I switch input channels on the amp, the buzzing goes
> away. So I tried putting the RCA plugs into a different input---no
> help.
> 
> For what it's worth, the buzzing sound is the same as if I pull the
> 1/8" plug out, and touch it to my finger---I'm sure this is a
> familiar sound to many people.
> 
> My guesses are that either the cable is bad (it's an el-cheapo,
> don't know where it came from) or the input jacks on my PC are
> crummy or not properly grounded. This sound is the kind of sound I
> would expect when my plug isn't properly seated, but, as I said,
> I've tried seating and re-seating it several times (across the
> different outputs), and still have no success.
> 
> Does anyone have any suggestions on my next steps to further debug
> this problem?
> 
> Thank you!
> Matt
> 
> -- 
> Matt Garman


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