Re: [TCLUG:7474] Semi-off-topic: Speaker noise

[Phil Mendelsohn <mend0070@tc.umn.edu>]

tclug-list-digest-help@mn-linux.org wrote:

> Subject: Re: [TCLUG:7474] Semi-off-topic: Speaker noise
> Date: Wed, 11 Aug 1999 12:32:02 -0500 (CDT)
> From: Yaron <jethro@yaron.org>
> To: tclug-list@mn-linux.org
> 
>   Hi,
> 
> On Wed, 11 Aug 1999, Joe Laha wrote:
> 
> > OK, I'm going to flex my AV geek muscles here. Buzzing in speakers usually
> > means something is not grounded correctly, check your speaker cables for
> > broken insulation, exposed wires..ect. After that try looking at your plugs,
> > make sure you're using three-prong plugs when plugging into the wall.
> > Hope that helps.
> 
> Well, since I tried with about 5 different self-amplifying speakers, I
> don't think it's a cable problem. However, the 3-prong thing gave me
> somewhat of a clue... all these speakers come with a 2-prong AC adapter.
> Anything I can do about THAT?

Well, I'm not a Linux guru, but I do have 15 years experience in analog
and digital audio electronics.

There are a number of things, but the first thing you need to do is make
sure that whatever speakers you use don't exhibit the same problem with
no source connected.  Here's how to check:

If you disconnect the cable from the computer and use some alligator
clips to short both channels to ground, you can safely turn on the
speakers.  (Keep the volume low at first.)  Turn them up.  If you still
hear the interference then you know the following:  Being an unbalanced
input you have no common mode resistance, and the input cable is acting
like an antenna.  If you're still getting the radio, something in the
amplifier is acting as a rectifier and turning it into a receiver.

If the buzzing is present, you should try flipping the AC adaptor over
(reverse the polarity.)  If you can't make the buzzing go away without
the sound card (or anything else) plugged in, you'll never be happy.

If the radio goes away, then the problem is most likely related to
improper grounding / decoupling on the actual audio card.  You would
want to verify this by testing with another audio card (if possible.) 
Also, the case of your computer might make a big difference.  Try
lifting the ground on the computer.

The important thing with finding grounding problems is to do one change
at a time -- start at the amp and work your way back.

Also, don't waste any time looking at speaker level cables -- if they're
shorted you get nothing but a hot amplifier!  And if they're not
grounded properly, you get no output.

Best,

Phil Mendelsohn
Chief Engineer
Hotdish Mastering