Audio hookup 4-wire PA system office

[edy]

Hi folks,

I"m trying to install a Sony receiver to play radio over an office PA that was just installed. See attached photos. From what I've read, the red/black is right and white/green is left. I am not sure whether both lines were used or just black/white. As you can see I have 2 cables each with 4 wires in them. But I don't know how they were connected to the PA.

There are 8 speakers total in the ceiling. Or 4 pairs. All I can assume is that there are 2 pairs joined in parallel on each cable. So 1 cable drives 4 speakers (2 on a red/black pair and 2 on a green/white pair). However speakers are all in different rooms so there is no real "stereo" effect anyways.

So if you see the attachment showing back of receiver, can I just hook up one cable with 4 wires to A and then the other to B? It is only 200W cheapo but I figure at worst it will just not be able to crank up volume. Could I damage anything like burn up receiver and/or speakers and/or volume pots?

[edy]

Update... I connected the pairs to A and B and A worked but B put receiver into protect mode. So I am trying now to figure out which speakers are working on the A and which are right/left and seeing what is causing the other 4-wire cable connected to "B" to trip protect circuit.

[David_AVD]

Hooking some unknown wiring up to an amplifier output is never a good idea.  That speaker system could be low impedance or 100V (or 70V) line.

Have you tried measuring the resistance between each combination of 2 wires?  (Disconnected from amplifier of course!)  That's your starting point.

[willb]

Hooking some unknown wiring up to an amplifier output is never a good idea.  That speaker system could be low impedance or 100V (or 70V) line.

Have you tried measuring the resistance between each combination of 2 wires?  (Disconnected from amplifier of course!)  That's your starting point.

This.

You definitely want to know the total system impedance before you start, especially where you're dealing with a consumer grade amplifier/receiver. Most of them will not handle anything lower than 8 ohms.

Wouldn't surprise me if your system is 70/100V. It's very common in commercial PA applications.  If you're in doubt, take one of the speakers out, if there's a transformer, it's a 25/70/100V system.

[edy]

Hi everyone,
Thanks for the help and advice!!! I trouble-shooted my installation and figured it out as follows:

I had 3 pairs working (white/green cable 1, red/black cable 1, white/green cable 2). That ran about 6 or 7 of the PA speaker/pots. However there were 3 not working. The red/black on cable 2 would cause receiver to "protect" mode and make click sounds as if a relay was disconnecting and power off.

So I opened up the 3 speaker pots for volume control that weren't working.

I noticed in one of the rooms, there was a single thin strand from a white wire that was bridged to the green!!! See the photo... I moved it out of the way, but that little bugger was causing a short! Argh!

The tech that installed the system didn't push it in properly.

Go figure!

Now it's fixed, works like a charm.

[David_AVD]

And still no measurement of the resistance to determine the likely load on the amplifier?  Sigh...  It makes sounds so job done I'm guessing.   

By the look of the volume controls they are low impedance type as the 100V / 70V ones are not usually stereo.

Some of those stereo units offer a "2x / 4x / 8x impedance multiplication" function so as to still present a reasonable impedance to the amplifier even when multiple units are hooked up in parallel.