Re: Switching audio via an Ocelot and SECU's

["John W" <Don't_Spam_Me@xxxxxxx>]

"Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote in message
news:wuWdnaHpD5yJVkLeRVn-sw@xxxxxxxxxx
> "John W" <Don't_Spam_Me@xxxxxxx> wrote in message
> news:66mdnUjmAdtIJUPeRVn-gg@xxxxxxxxxxxxxxx
>> Since you are using amplified speakers, the SECU16 relays will easily
> handle
>> the line level (i.e. unamplified) audio that you need to feed the
> speakers.
>> The 38W you refer to is the output of the amplifier in the speakers.
> Input
>> to the speakers is a relatively low voltage (line level) like that put
>> out
>> by the sound card in your PC.
>
> Yes - but my concern is still that the low voltage line level inputs will
> be
> subjected to hum if run through unshielded wire.  I've seen people tackle
> this with baluns, mini coax and other forms of ground loop isolation and
> still have hum issues.  I'd hate to wire it up and find out that there's
> some sort of unresolvable hum issue.

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?

>> 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 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?
>
> 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.
>
>> 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.

John W
>
> --
> Bobby G.
>
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