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Ghost in my PA system

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Ghost in my PA system

Postby liveguitar » Mon Nov 25, 2019 4:41 pm

Good morning/afternoon/evening,

Issue with my passive PA speakers/amp.....

Yesterday after playing a gig, I had background music playing when I noticed one of my speakers wasn't working. There was nothing coming from the woofer, and a very slight low level top end coming from the horn. It was working perfectly for sound check and at the start of the gig, but since I wasn't near that speaker, I don't know at what point it stopped working, but I didn't notice any level drop at all during the performance.

I stuck some tape on the side of the speaker so I knew which one to check, however my mate kindly removed the tape when he was 'helping' to pack away. Anyway I set everything up in the garage today to try to isolate the problem. Again one speaker working fine, and the other nothing from the woofer and a very slight top end from the horn. My first check was to turn off the amp, swap the speakon cables round at the output of the amp (channel A to B, and B to A) and try again. This time both speakers were working perfectly. I switched the cables again to how they were initially, and both speakers were still working perfectly.

Can anyone tell me what the issue might be, and how I can prevent it?

The speakers are (Thomann) 'the box PA502', and 'the t.amp E-800'. I've been using the same setup for around three years and have never had this (or any other) issue.

Any help will be greatly appreciated,

Warren.
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Re: Ghost in my PA system

Postby Hugh Robjohns » Mon Nov 25, 2019 6:34 pm

liveguitar wrote:My first check was to turn off the amp, swap the speakon cables round at the output of the amp (channel A to B, and B to A) and try again. This time both speakers were working perfectly. I switched the cables again to how they were initially, and both speakers were still working perfectly.

Can anyone tell me what the issue might be, and how I can prevent it?

I'd guess at loose screw connections inside the Speakon connectors (probably at the amp end), or Speakons not connected properly, or dirt in the connections, or possibly damaged cables.

I'd certainly start by opening and checking all the Speakons for the tightness of wire connections. They can and do work loose over time. Also a squirt of deoxit on the connector pins in the plugs, amp and speakers wouldn't go amiss. And

check the cables for any obvious signs of damage -- especially crush damage from being stood on, or having something heavy rolled over it.

The fact that both speakers work properly from both amp channels implies the amp and speakers are still fine.

H
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Re: Ghost in my PA system

Postby AlecSp » Mon Nov 25, 2019 8:11 pm

Hugh Robjohns wrote:I'd guess at loose screw connections inside the Speakon connectors (probably at the amp end), or Speakons not connected properly, or dirt in the connections, or possibly damaged cables.

I'd certainly start by opening and checking all the Speakons for the tightness of wire connections. They can and do work loose over time.
Completely agree that this is the most likely cause, based on my experience. All it takes is one tug to free the conductor from the terminal in the plug. After that, you can end up with an intermittent connection. The good news is that it's easy to check (unless you have the earlier NL2 speakons which were a crystal maze to open up.

Hugh Robjohns wrote:The fact that both speakers work properly from both amp channels implies the amp and speakers are still fine.
Not necessarily! Although my money's still on the speakon cables, you could have an amp channel that is OK for a while, and then croaks as it warms up (though the fact that swapping over the cables resulted in things coming back to life makes this less likely). Or you may have an intermittent connection in the speaker or (less likely) in the amp.

None of the above is guaranteed to be the cause, but it would be surprising if it wasn't.
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Re: Ghost in my PA system

Postby Hugh Robjohns » Mon Nov 25, 2019 8:32 pm

AlecSp wrote:
Hugh Robjohns wrote:The fact that both speakers work properly from both amp channels implies the amp and speakers are still fine.
Not necessarily!

Indeed! ;-) And that's why I said 'implies' and not 'confirms' :lol:
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Re: Ghost in my PA system

Postby liveguitar » Mon Nov 25, 2019 9:26 pm

Thank you for the advice. I did check the cables (wiggled them in the sockets). I will give them a thorough examination tomorrow afternoon.
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Re: Ghost in my PA system

Postby AlecSp » Mon Nov 25, 2019 10:53 pm

liveguitar wrote:Thank you for the advice. I did check the cables (wiggled them in the sockets). I will give them a thorough examination tomorrow afternoon.
It's less about wiggling them in the sockets than wiggling the cable going into the plug.

But it's *completely* about opening them up and seeing if the conductors are secure in their receptacles - you can do this in under 30 seconds per end.
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Re: Ghost in my PA system

Postby liveguitar » Sat Nov 30, 2019 10:53 am

Thank you all for the help.

Dipstick of the month award goes to me......one of the j-j cables I use between the mixer and the amp has a loose connector.
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Re: Ghost in my PA system

Postby AlecSp » Sat Nov 30, 2019 5:25 pm

It's always the last place you check, right? ;)

You could do worse than buy a cable tester - it will prove its worth time and time again in helping debug problems. Popular options include the Behringer CT100 and the Studiospares Ultimate testers. Both work quite differently, and both are heavily defended by their fans. I use the CT100.
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Re: Ghost in my PA system

Postby Sam Spoons » Sat Nov 30, 2019 6:24 pm

I have both and the Berry power switch is a minor annoyance as it's easy to accidentally switch it on when putting it in a bag, also it doesn't have Speakons. It's more convenient in use though as you can just plug the lead in and check all conductors in one go instead of stepping through them one at a time. It also does intermittent faults better.
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Re: Ghost in my PA system

Postby Wonks » Sat Nov 30, 2019 6:36 pm

Sam Spoons wrote:It also does intermittent faults better.

No it doe...

Yes it do...

No it doesn.....

Hold on...

Yes it does....
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Re: Ghost in my PA system

Postby AlecSp » Sat Nov 30, 2019 7:25 pm

Sam Spoons wrote:I have both and the Berry power switch is a minor annoyance as it's easy to accidentally switch it on when putting it in a bag, also it doesn't have Speakons. It's more convenient in use though as you can just plug the lead in and check all conductors in one go instead of stepping through them one at a time. It also does intermittent faults better.
And those are some of the reasons why no-one can agree on which is better. Quick tip on the power switch, why not file it down so it doesn't catch on things in the bag, but can still be easily operated when you want to turn it on. I had the same problem as you - now fixed :D
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Re: Ghost in my PA system

Postby Sam Spoons » Sat Nov 30, 2019 7:46 pm

Great idea :clap: The alternative is to cut a small rectangle of camp[ing mat with a small slot for the switch and stick it in with double sided tape. It does hide the legends but you'd probably have filed them off when you filed the switch anyway.....
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Re: Ghost in my PA system

Postby AlecSp » Sat Nov 30, 2019 9:25 pm

Sam Spoons wrote:It does hide the legends but you'd probably have filed them off when you filed the switch anyway.....
Actually, I said "filed", but I think I used a craft knife in the end.

Also, my CT100 tends not to come out with me that much since I picked up a Rat Sniffer. Hugely light, only does XLRs, but they're most of what I need, and perfect to put on either end of a snake to find faults.

That was one weakness with the CT100 - I wanted to test a 40m snake, so plugged a long XLR into it to get both ends in the CT100 - it registered something strange (can't remember what) which I put down to the overall length being too long. Yes, I know it has its installed cable mode, but that's less functional.

But I love the instantaneous display and the intermittent fault detection.
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Re: Ghost in my PA system

Postby Hugh Robjohns » Sat Nov 30, 2019 10:02 pm

AlecSp wrote:Also, my CT100 tends not to come out with me that much since I picked up a Rat Sniffer.

A variation on a phantom-power checker.

Lots of similar items are available from many manufacturers, albeit with slight differences in functionality. And a DIY version isn't too hard to construct, if you're that way inclined! But all will identify faulty XLR cables immediately -- provided phantom is available, of course.

Some just give a go/no-go indication while others will identify the nature of the fault in more detail. Some will confirm whether the phantom supply can deliver adequate current, too

I have a couple of DIY versions, both on keyrings (built into Cannon XLRs which lend themselves to keying mounting!), and one has been in use for 30-odd years! I never attend a session without one or other!
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