Niall Blackburn
From Christ Church Woking
8 March 2010 - 9:38am
So I was leading worship last night, and my microphone started to distort when i started singing loud. At first it was going through a samson s-monitor, so we took this out of the equation, and that helped, but it was still doing it.
Here's what the signal chain was:
Shure beta 87c
box at the side of the stage
desk up top (Allen and Heath, Older GL series)
d&b d6 or d12 amps
d&b speakers and subs (not quite sure of the models... possibly Ci)
Now here's the weird thing, my mic hasn't done this before, and we've had a similar issue with the churches Sennheiser e845. Now it wasn't peaking on the desk...... any ideas as to what's going on?
Me and our worship pastor are going to test it out today, check different channels, see if we can get the same problem using different mics, cables, check the amps. I'll give you an update, but if you have any suggestions before that!
irish_admiral
From Cardiff Vineyard
8 March 2010 - 10:17am
Niall
Assuming all your other trouble shooting fails to highlight any problems, here are my thoughts... If it's only the mics, and they're both doing it, chances are that someone has got the gain level at the desk running too high, or has taken out a pad that was there previously.
Do you run it through a compressor or any other outboard gear? If the gain going into that is too high, it can distort also.
But that fact that you've had it with both mics when you didn't previously suggests that it's something to do with the FOH end of things... it's pretty unlikely that both mics would suddenly develop a fault.
No comps or outboards!
And the guy on sound tried with the pad on and off, the blinking lights on the desk weren't peaking, they were where they should be.
When it happened with the other mic, it was labelled as broken, but my dad decided to try the next week, and had no issues with it, but had issues this sunday morn! As for my mic, this is the first time it's happened, and my dad said he had problems with both vocals in the morning. But yeah, we'll have a test this afternoon, check out the sennheisers, my beta 87 and 58, and the sm58s and see if anything is obviously wrong!
it may be the ch on the desk so try it in another ch. also try on another desk if possible just incase it is the desk.
colin
Yeah, as colin said.
The peak limiter lights on the desk aren't always the best indicator - got you use your ears too. Although those old A&H desks are fairly sturdy and take some driving so i'm not sure.
I'd still try dropping the gain at the desk to see if it solves the problem. May as well rule it out.
most Allan & Heath Desks the desk ch's are on there own boards so if it is a desk ch it can be replaced by someone who knows what they are doing. if you contact Allen & Heath to find that person and to see if the board is still available.
colin
Niall...
If it is the desk, then John Godsland at Orchid Electronics is a registered A&H (and 'old' A&H desks!) repair engineer. We've had dealings with him a few times for other bits and pieces and he's a nice guy, very genuine. He's down in the southwest though, so may not be ideally located for you.
http://ftp2.dns-systems.net/~orchid/index.htm
He also does a very good DI box for not a lot of money, and his acoustic preamp is very good too, so I hear. He's one of those repair techs who does a bit of everything for sound gear - take a look at his custom products page!
At the risk of being accused of teaching youth-challenged-multigenerational-matriarchs to digest eggs. I'd make sure and check any cables first - 9 times out of ten it is down to the cables.
Two main causes of distortion with A&H GL series desks that I've come across before.
1) Brown outs - check your mains supply, the 48V rail on most old GL isn't the most stable in the world and can react badly to a drop in power from the mains. Remember that when these desks where produced the power supply in the UK was 235-245V, it is now 220-230V. Doesn't affect most things, but some equipment will now have bad days. Also a problem if you have lots of condensors and active DI boxes hanging off your desk as the PSU can become overloaded. Brown outs can also reduce the power rails to the op-amps and this will cause premature clipping.
2) Dirty faders! Older desks will suffer from worn/dirty fader tracks that can introduce a range of faults from crackles through slight distortions to in the worst case dead patches on the fader. Next time the distortion happens, try giving the fader a good waggle - if it drops completely, crackles or suddenly comes back then it's time to get those faders looked at.
John Godsland is a most excellent recomendation, I push their pre-amps on anyone I work with who really cares about how their accoustic instrument sounds. And the genius of a mic-stand mounted mute button cannot be underestimated!
Hope this helps.
Gareth.
Hi Gareth
That's an interesting one... how do you rate his acoustic preamp against others? I run a K&K Trinity system on my Eggle, and the pickup still takes a cut at around 650hz, the mic at around 1.5khz at the desk. When it sounds good, it's very good, but some guys have had off days with it. I'm never quite sure i'm perfectly happy with it.
Would be interested in your thoughts of John's stuff versus eg. the Baggs PADI, Headway EDB1, BBE Acoustimax etc...
Oh... I try to keep mute buttons away from the stage. Too many occasions we have the muso complaining, "there's no sound!" on whatever, not realising they've muted it. They have enough trouble remembering when the cable is or isn't plugged in to be worrying about mutes.
Classic example, our pastor bought SM58s with mute switches as he thought it would be a good idea. Two services later, I had made my point, we taped over the switches, and it has remained thus since...
... therein lie the perils of pastoral staff buying sound gear without consulting first...
Have you ruled out the possibility of a dodgey mic cable? :)
TM
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