Re: Switching audio via an Ocelot and SECU's

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"John W" <Don't_Spam_Me@xxxxxxx> wrote in message

<stuff snipped>

> Twisted pair is not as good as shielded but it is cheap and what they
> connect telephones with.  Given that same wire is capable of carrying a
> broadband signal (DSL) for several kilometers, it should (and, in my case
> does) handle line-level audio adequately.  If you have any around, you
could
> do some bench testing before installing anything?

You bet I will before I go fishing cable through the walls! :-)

> >> I use PC-style amplified speakers for my whole house audio and have no
> >> problems with buzz or hum even though some of them have 50 feet of
cable
> >> connecting them.  I use regular telephone cable (twisted pairs) for
> > cabling
> >> and buy it in boxes of 1000 feet for under $30.  I use the same cable
for
> > my
> >> PIR's and other SECU inputs as well.
> >
> > It could be that you're just lucky not to have any hum issues.
> > Unfortunately, I've already discovered I couldn't run one set of
amplified
> > speakers through 3 position RCA stereo switchbox without outrageous hum.
> > I
> > was trying to switch inputs from a small TV, a PC and a portable MP3
> > player
> > into a set of amplified speakers and as soon as the RCA cable from the
PC
> > was plugged in, there was an outrageous hum problem.
>
> RCA jacks/cables normally carry amplified signals

????  On most of my stereo equipment, the red and white RCA jacks are used
to connect line level devices.  The only time I've seen RCA connectors carry
amped signals was with an old, suitcase style phonograph player or are we
talking about different things?

>  so I'm not sure what you
> were switching?  Line-level audio normally uses the 1/8" earphone style
> jack/cables like MP3 players and PC sound cards use.  Was the hum 60cycle?
> If yes, it's probably a grounding issue between the devices your are
> switching?

The switchbox had RCA style jacks for switching line level audio.  I
connected to it with a mini-stereo 1/8" phone plug to two RCA plug cables.
And yes, it's probably a grounding issue and one that was impossible to
solve.  I ended up using a two sets of speakers and a mini-stereo extension
cable so that I could connect and disconnect the PC and the MP3 player from
speaker input manually.

> > I'm anticipating a number of devices feeding into the SECU audio
switcher
> > with the output going to at least 3 sets of amplified speakers.  My gut
> > tells me at least one of those combinations is going to hum if wired
> > through
> > twisted pair.  But I can simulate it pretty easily with uninstalled
CAT-5
> > pieces I have lying around before I go through the trouble of pulling
> > cable.
> > I just think the electrons in Canada behavior themselves better in audio
> > systems.  :-)
>
> Candadians do generally behave themselves quite well (even Canadian
> electrons ;-) but a test with CAT5 sounds like a good idea.  Just be sure
> you are carrying the unamplified (line level) signal on it so the CAT5
goes
> from the PC soundcard output (example) to the amplified speaker input.

Candadians?   Are they the male of the species?  :-)

> >> So far, I have not tried switching audio sources with SECU relays but I
> > may
> >> do that to switch from my SpeakEasy to my PC sound card so I can play
> > MP3's > from my PC on the same speakers.
> >
> > That's where I think you might run into hum and crosstalk issues.  Of
> > course, I live within a few hundred meters of a big cell tower, so that
> > might explain why hum is a bigger problem for me.
>
> You may also recall from previous posts that all of my SECU relays connect
> to my relay board and are only used to switch these 10a DPST relays.  This
> provides isolation and higher current carrying capacity.

 My feeling is that there was a problem in the audio switchbox but another
make and model behaved the same way.  What the TV and the PC were using for
their audio ground weren't compatible.  As for testing, since I am a
wood-worker by genetic disposition, the command "measure twice, cut once"
has a counterpart in the electronics world.  "Test twice, then hookup."

--
Bobby G.