Hi all,

I'm new round here so go easy on me!

I run a bar, and we quite regularlyhost live music in our upstairs room. At some gigs I look after the sound myself - I did bits and bobs on this front when at uni and there's nothing particularly complicated to it, the rooms small and all that's needed through the PA is vocals and the occassional keyboard/sax/etc.

I have an occassional problem where my amp starts clipping for no apparent reason, the output meters from the desk and EQ are showing the same and the limiter hasn't been touched (the amp also has an in built clip limiter). We had a gig the other night where the first band on played about 1/2 hr after their soundcheck and nothing had been touched, but the clip LEDs on the amp were flickering straight away. I initially put this down to an adrenalin rush on the singers part, but all the meters seemed to show the same levels going into the amp.

It then occurred to me that we're next door to a rather large (1500 seat) theatre and they had big show start in the intervening time. Could I be right in suspecting that they suddenly started drawing a lot more power thus degrading my own supply? And if so, would this cause the amp to clip at a lower signal level?

I actually have a degree in elec & elec engineering, I have a good understanding of the theory of how amps work but I've got no idea of what sort of transformer you would typically find inside the box (the amps a Tapco Juice 1500, hardly top of the range, indeed is this a problem that you would find on a cheap amp but not higher end stuff?)

Thanks for your time, and in advance of any advice. I hate to ask for help without being able to offer any myself, but looking through past threads it seems that most of you have WAY more expertise than I'll probably ever have. That said I do have an extensive knowledge of licensing laws and other venue management type stuff so if anyone needs advice there I may be able to help.

Cheers,

Matt

ps I did use to deliberately push the amp until the clip LEDs flickered in an attempt to squeeze just a little more out. Learnt my lesson on that front the expensive way! But looking through past posts here educated me in what I was doing wrong in quick time so thanks for that too!

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One is too many, two is about right, but three can never, ever, be enough

In theory yes, you can have degraded performance of an amp with a less than ideal power supply. Whether this would cause the amp to show on its clip light or not depends on exactly how they determine the clipping though. This is the reason that power conditioning is standard on any touring rig or installed system once you get past entry level stuff(No offense intended). It is easy to damage things with less than ideal power, but even if it still runs, it might still be degraded.

Seablade

If the mains supply was fluctuating you would probably notice the lights going dimmer before you would notice problems with the amp clipping.

Cheers

James.

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JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

Maplin sells a really handy mains power checker that you can just plug in to see what the mains voltage is (it also tells you the current being drawn, power factor and various other things). You can find it here (L61AQ, £28)

That will let you know if there is a mains voltage issue.

The other possibility is that the amp is overheating and protecting itself, or that there are out of band signals getting into the amp that you can't hear, but enough to upset it.

Hugh

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Technical Editor, Sound On Sound

Quote:

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Maplin sells a really handy mains power checker that you can just plug in to see what the mains voltage is (it also tells you the current being drawn, power factor and various other things). You can find it here (L61AQ, £28)

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Or here http://cpc.farnell.com/PL09919/electrical-lighting-security/product.us0?sk u=PRO-ELEC-2022MU&_requestid=60822 a little bit cheaper

I have one - it's quite an eye opener - amazing that some stuff uses nearly as much juice on standby than when its on!

Cheers
Anton

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You see when I was a young kid Elvis was top of the charts - That's 'Presley' not Costello!

Thanks guys, time for some investigating methinks...

*puts on dearstalkers and lights pipe*