Setting up a PA (Amp, speakers, mics)

Peerzy · 12 Feb 2013 at 18:45

Right so I've been asked to setup a very very basic PA system, problem is I've only ever done this once before - years ago and with someone else doing most of the work.

The setup is as follows

* 4 speakers (Front Left, Front Right, Rear Left, Rear Right) that each have two cables for me to play with (speakers have been installed already by an outside company).
* Amp / Hi-Fi thing
* Wirelesss Mics (x2) and wireless receiver
* Laptop (Will be used to audio out)

The laptop I'm fine with, ditto the wireless Mics which I've got connected to the wireless receiver without issue. The problem I'm having is cabling it all together.

Below are some photos of the kit;

Front of kit
Rear of kit

This is how far I've got with cabling it up:

Image 1
Image 2
Image 3
Image 4

So not totally complete. The red and black RCA cable plugs into the headphone socket of the laptop. I'm not sure the wireless box to the Amp is wired correctly. The wireless receiver is connected to the Amp with a big audio jack into the 'Link In' hole in the images, not sure if that's right.

I'm after some advice as what I require to get this all working and where I plug what!?

Also have I connected the speakers up correctly? Each speaker has 2 cables which I've screwed into 1 single speaker channel on the Amp / HiFi thing?

Any advice welcome, I'm sure I'm just missing a couple of cables plugged in the right holes.

Lakeland · 12 Feb 2013 at 18:52

It's hard to see but have you not flipped the switch to PHONO on Channel 6 in the first photo? I'm guessing that's why your laptop isn't working.

On second look it seems you have plugged the wireless mic in to the Link In rather than the channel in, grab a XLR to XLR cable and input the mic in one of the channels 1-5. Always better using balanced outputs as you won't get any interference from mobiles going off!

Peerzy · 12 Feb 2013 at 18:53

Lakeland said:
It's hard to see but have you not flipped the switch to PHONO on Channel 6 in the first photo?

At the moment it's on PHONO which is what it arrived on, although I did try both settings.

I'm fairly certain I'm missing some cables though so no matter what setting I wouldn't get any output on the speakers.

Assume you are talking about the PHONO / MIC AUX switch on the back in the second photo.

Dangerous Dave · 12 Feb 2013 at 19:01

You have the speakers connected incorrectly, the negative cable needs to go in the common terminal, this should be the one with the black line but you will need to check what this is connected into on the speakers. The live then all go into the 4 or 8 ohm terminal. Do you have a photo or make model of the speakers ? You check the impedance setting depending on what speakers you are using and also check the minimum impedance the amp can run 4 speakers with.

Peerzy · 12 Feb 2013 at 19:05

Unfortunately the speakers are mounted into the ceiling, of a sports hall. The speakers are absolutely out of bounds and I've got no chance of getting anywhere near them let alone working out what one is negative.

What is the common terminal and where is it on my amp?

Lakeland · 12 Feb 2013 at 19:08

Peerzy said:
At the moment it's on PHONO which is what it arrived on, although I did try both settings.

I'm fairly certain I'm missing some cables though so no matter what setting I wouldn't get any output on the speakers.

Assume you are talking about the PHONO / MIC AUX switch on the back in the second photo.

That should work if it's on Phono then. The reason you are getting no sound is because the + and - are shorted out (connected to each other) on the amplifier. You need to connect + on the amp to + on the speaker terminal (it should be labeled as such) and the same with - .

That allows + to go in to the speaker, and come back out through the - back in to the amplifier. At the moment the power is going out of the amp and straight back in, if the amp doesn't have protection it could go pop so if it's turned on get the cables taken off asap.

Peerzy · 12 Feb 2013 at 19:09

Lakeland said:
That should work if it's on Phono then. The reason you are getting no sound is because the + and - are shorted out (connected to each other) on the amplifier. You need to connect + on the amp to + on the speaker terminal (it should be labeled as such) and the same with - .

That allows + to go in to the speaker, and come back out through the - back in to the amplifier. At the moment the power is going out of the amp and straight back in, if the amp doesn't have protection it could go pop so if it's turned on get the cables taken off asap.

Understood, so say I manage to somehow work out which of the cables for each speaker is positive and which is negative where should I put them?

Lakeland · 12 Feb 2013 at 19:14

Peerzy said:
Understood, so say I manage to somehow work out which of the cables for each speaker is positive and which is negative where should I put them?

http://www.inter-m.com/super/english/upfile/opmenual/PA-2000A_4000A_6000A_me.pdf

This should help, there is a page which shows how to wire the speakers in.

You can wire speakers in reverse as long as you do the same to all of the speakers. Unfortunately you are relying on the installer wiring them all in the same, which they should have done unless they are inept. Considering what you are setting this up for, there won't be any issues with equipment, only sound quality as wiring speakers out of phase ( one speaker + to +, - to -, and the other + to - and - to + ) doesn't = the best sound quality

Dangerous Dave · 12 Feb 2013 at 19:18

Peerzy said:
Unfortunately the speakers are mounted into the ceiling, of a sports hall. The speakers are absolutely out of bounds and I've got no chance of getting anywhere near them let alone working out what one is negative.

What is the common terminal and where is it on my amp?

The common terminal is the COM post, you need to know the impedance of the speakers so you know how to plug them in. If the speakers are 4 , 8 or 16 ohm the positive cable will go into the 4 or 8 ohm output depending on the rating.

If they are high impedance speakers each speakers positive cable with go in the 1, 2, 3, & 4 terminal with all the negative cables going into the COM terminal. At a guess I would expect if the amp was provided by the installers of the speakers that the ceiling speakers will be high impedance.

I would try one speaker first with the black lined cable in the COM post and the other in the 1 post and see if you get a sound output. If that works add one at a time.

The manual for the amp is here

http://www.inter-m.uk.com/pdfs/operation_manls/pa4000a_opmanls.pdf

Peerzy · 12 Feb 2013 at 21:46

I guess I've really got to find out the make and model of speakers then, annoyingly none of the cabling is labeled up as positive or negative so that could also cause some problems.

Apart from that have I got everything else setup as it should be?

lucid · 13 Feb 2013 at 08:46

Some of this will have been covered in other posts, but I'm just going to post a complete guide for the sake of completeness...

The laptop input going to channel 6 is fine so long as you move the selector switch to Mic/AUX and then rotate the MIC ATT dial all the way anticlockwise to the AUX position.

The wireless mic input in to LINK IN is wrong. That's for a tape deck loop. Since it looks like you just have the 1/4" jack to jack cable then connect it to the Front Panel CHANNEL 1 input. Set the rear panel Ch1 MIC ATT knob all the way clockwise to MIC.

Your front input controls on the amp (Chnls 1~6) operate like a mixer. The MASTER control gives the overall level of the entire mix.

The tricky bit for you is the speaker connections. Looking at the cable I'd say you have 8 Ohm speakers. If it was a 100 Volt Line install then the cable carries a high-ish voltage so needs to be double insulated (like you see on mains cable) so the conductors aren't exposed if the outer sheath is accidentally broken open. However, to be 100% sure you really need to see the back of one of the speakers.

An 8 ohm speaker will look like this with a conventional set of speaker terminals

If it is 100 volt line then it will look something like this with a transformer

Better quality 8 Ohm speakers will have crossover components. These may well include large copper coils. Don't confuse these with a transformer. A transformer will have a metal bridge arching over an insulated coil.

Next is the cable polarity. Nearly all speaker cables have some way of identifying one conductor from the other. If it isn't colour coded then there's almost always a ridge on one conductor sheath. Your cables are colour coded with a black stripe. Once you see the back of a speaker then you'll know whether black stripe goes to black (-ve) or red (+ve).

The speaker connection for 8 Ohm is all the black terminal wires to the COM connector. All the red terminal wires to the 8 Ohm connector. This presumes that all your speakers are a minimum 8 Ohm impedance. If they are lower than 8 Ohm then connect all the positives (red) to the 4 Ohm terminal on the amp instead.

Peerzy · 13 Feb 2013 at 09:05

Brilliant, thanks lucid that helps massively.

The only thing is that I maybe able to find out the make and model of the speakers but there is no way of getting to them or seeing the cabling. It's a sports hall and the speakers are in the ceiling which is a good 30ft above the floor.

Can I 'guess' that the black is positive or negative? I was told all the speaker cable wiring was done 'as you would expect', so if there is a standard or normal practice I think it's best for me to assume they've followed that.

Dangerous Dave · 13 Feb 2013 at 23:02

lucid said:
The tricky bit for you is the speaker connections. Looking at the cable I'd say you have 8 Ohm speakers. If it was a 100 Volt Line install then the cable carries a high-ish voltage so needs to be double insulated (like you see on mains cable) so the conductors aren't exposed if the outer sheath is accidentally broken open. However, to be 100% sure you really need to see the back of one of the speakers.

Wouldn't 4 8ohm speakers wired in parallel result in a 2ohm load to the amp which it can't support ?

AshD93 · 14 Feb 2013 at 00:06

Dangerous Dave said:
Wouldn't 4 8ohm speakers wired in parallel result in a 2ohm load to the amp which it can't support ?

He can run it at 8 Ohms.

2 speakers in a series "pair" x 2 >>> Connect the two new "pairs" in parallel

OR

2 speakers in a parallel "pair" x 2 >>> Connect the two new "pairs" in series

Or 32 Ohm's if he runs in full series but he'll be lacking serious power.

or 2 Ohm like you said and risk the amp. I've done 4 Ohm on a 6 Ohm Hi-Fi amp and it was fine. Though it was a solid Technics amp.

lucid · 14 Feb 2013 at 08:04

Although I agree with both above posts, the amp instructions do show all the speakers connection in parallel. Personally though I'd go with the 8 ohm solution.

As for whether the black stripe is for positive or negative. It doesn't really matter. The convention is to put the marked cable to the red (+ve) connection, but equally the installer could have decided it's a black line so hook it up to the black connector (-ve). As long as all the speakers are wired the same way then it doesn't matter.

Peerzy · 14 Feb 2013 at 09:31

Cool, I'm having a go this afternoon.

I'm going to print out the posts here and try my best.

If we assume they are 8ohm then all the wires with black will go into the COM port and all the cables with nothing into the 8ohm port.

If they are 4ohm then the same as above but into the 4ohm port.

Plug wireless receiver into the Channel 1 port on the front instead of the line out on the back.

Am I likely to blow up anything if I wire them into 8ohm or 4ohm, considering how I had them wired and I did turn the amp on and the volume / master volume up to max?

BTW which COM port do the speaker cables go into? There are 2? Or does it not matter?

lucid · 14 Feb 2013 at 12:27

The COM ports are the same. There's two because there might be quite a few cables going to the amp if using the multi-zone 100V line feature.

For wiring the speakers, I'd recommend you go with the series/parallel arrangement outlined above. Use some 5 AMP connector terminals to make it easier to handle the various connections between the amp and the speakers. If you haven't used this kind of choc block connector before then all it is is metal conductors with a couple of screw clamps in each to secure the cables. The plastic can be cut so that individual or groups of conductors can be separated off.

As for whether to use 4 Ohm or 8 ohm; it is always safer to have the amp driving a higher ohm load. So 4 Ohm at the amp in to an 8 Ohm load is safer than 8 ohm on the amp in to a 4 Ohm load. However, the greatest efficiency is achieved when the speaker load* matches the ohms output on the amp.

Edit: Oh yes, I nearly forgot. The reason you didn't blow anying up when you wired the speakers before is that there was actually no load on the amp. You need a connection across the COM and 4/8 Ohm terminals (or the 100V line equivalents) before the amp will deliver any power.

* For those about to chime in that the speaker resistance isn't fixed, and that it varies with frequency and the operating efficiency of the transducer - hence nominal impedance rather than fixed resistance - Yes, that's all true and you are correct. However, it goes beyond the requirements of this thread and as such would just serve to confuse rather than enlighten.

Peerzy · 16 Sep 2013 at 14:21

A rather late update, I did wire this as I said I would and everything was brilliant. Over the summer the hall had a new floor put in so someone has unwired the amp and now I need to wire it back up again!

Easy I thought considering I took pictures after I'd done it last time and had this thread. However now whenever I turn the amp on the 'PROT' light stays on for a while (sometimes up to 10 minutes), the amp is then fine to use - although at random intervals it will completely cut out and the 'PROT' light will light up red.....

The amp is an 'InterM PA-4000A' and I've wired all of the cables with black lines into the COM port and the rest into the 8Ohm port which is exactly what I did before (previously the amp didn't have this issue).

Obviously driving the user mad as they cannot really use it at the moment - any ideas?

A quick google seems to suggest the amp is protecting itself, although I don't know why it would suddenly start doing this now.

lucid · 16 Sep 2013 at 15:06

Yes, Prot for Protection. Doesn't really take Sherlock Holmes to worth that out though

The most likely cause is a short in the speaker cable. This short could be something as simple as a fine strand of copper bridging between the positive and negative terminals. Equally common is someone has tacked up the cables and gone through with a nail or staple somewhere.

Less common faults would be switching the AC power selector from 240V to 110V (though I'd expect an accompanying bang and the smell of burned out diodes); stripping cable over the amp and shedding filaments of copper in through the cooling vents on to the amps circuits (protection mode would be a lucky escape); abuse of the amp causing some heat stress; knackered capacitors, a fault on a source device.... the list goes on and on.

You can help yourself by doing a little trouble-shooting and diagnosis. Start off with the amp unplugged. Disconnect all sources and all speakers. Check the speaker terminals are clear of any bits of copper filament. Set the volume control to 50%. Plug in the mains then try the main power switch. If the amp comes on normally then you can guess that it's either a source or speaker related issue. If it's still in protection with nothing connected then it's an amp fault.

If the amp worked okay this time then power off and add one source device. Power on again (still no speakers) and see if it comes on properly. Keep going adding sources until you eliminate them all as either okay or you have isolated and removed the problem source.

If you're still good at this point then add the speakers. If the amp goes in to protect then you have some work to do on the speaker side. Just work through methodically. Add one speaker at a time until you find the problem.

Peerzy · 16 Sep 2013 at 17:44

Thanks, I'll have a work through it tomorrow.

The protection light came on and stayed on when I had all the speakers disconnected so I can only guess to remove the other bits and pieces but the amp might be the issue.

It's very odd that it works eventually and then cuts out, but I know sod all about this sort of stuff.