Triac hash noise and stage amps/mixers.

Does he get the noise with all inputs turned down and with no cables plugged into any inputs? Is it all balanced lines on input and output?

Chances are it's a cabling problem, or an earth missing. Does it have a built in effects unit? ( a prime colector of interferance)

What make and model of mixer is it?

Ron(UK)

A smart chappy eh ?

Duh !

More to the point. How on earth is mains noise getting in to the mixer electronics in the first place ?

Graham

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Phonic 12 Impact ,12 channel mixer, 25 x 16 inch , all steel cased and no earth bond problem. No internal effects , no known inputs problems and he has swapped inputs and leads and instruments and would suggest a problem with the mixer.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I would start with the source of the noise and not so much as trying to filter it out. I don't think there is a problem with the mixer. I've gigged on and off for 20 years and noise from dimmers and dimmer/lighting packs is a fact of life.

But does it buzz with no input cables in? If not, it`s a cable problem, probably using an unbalanced line in for guitar (or some other instrument) instead of a balanced line into a microphone input and a di box.

The correct fault finding method is to strip it back to basics to see where the hum gets in, if it`s coming up the mains cable, you probably have a struggle on your hands, it IS a budget mixer.

Ron(UK)

Not really.

Have you checked he's got his mics wired balanced and that they're on XLRs?

Musos have been known to plug mics with 'mono' jack plugs into the line inputs and crank the gain to max to compensate.

Graham

Yup, it's far more likely to be a cabling or earth loop type problem.

Check all the points Ron made too.

Graham

I've yet to come across a pro mixer not designed for this sort of venue - so I'd look to the earthing etc if you're certain it's not being picked up on the cables. Unless of course the mixer is situated right beside a dimmer trolley. If it is a cable problem, star quad is likely to sort it.

Worth also checking any DIs in use - some don't make a decent job of balancing their output.

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I'm not going to start going to his gigs, as they are quite distant regular venues, so will have to coach him for what to look for. He plays with another using in all about 10 instruments/mikes and it seems its a consistant problem, constant level problem, at those 2 venues , whatever instruments/cables. They play seated but I'll ask one to move around at sound check and get the other to monitor for any change in hash level which should vary if induced from the lighting cabling via air into signal leads, cf mains-bourne should be constant level. While I've got the mixer here open for a minor repair I'll fix a 3 amp in-line small off-the-shelf standard C/L filter inside , on the mains feed.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Again I'd be amazed if the PS doesn't include decent filtering - after all even the cheapest mixer is likely to be used along with light dimmers. Many will pick up heavy interference nearby though - hence not having a mobile phone close to them - due to being unbalanced internally. As I said, I'd ask if it is situated close to a dimmer rack etc at the location where it gives the problem. And if it is, the only practical way is re-siting either, as screening will be very difficult.

It`s a constant level? Do you mean it doesn`t change with the level of the light dimmers? Dimmer hash is pretty instantly recognisable to anyone in the business of PA hire, it changes in 'tone' as the lights are brought up and down. Are there any neon signs in this venue? they kick out all sorts of nasty chit, but nothing a properly set up rig can`t reject. i.e. fully balanced lines in and out.

Just tell then to disconnect each channel in turn till the buzz goes away. If it still buzzes with no inputs, it`s the desk, or the cables to the power amps. It`s not impossible that it`s being induced into the speaker cables.

Also, make sure that they arent using el-cheapo mains fourways for distro, sell them some decent quality ones - I like the orange Permaplug ones.

It might be some kind of mains phase issue. Usually stage lighting is spread across all three phases, but sometimes it`s all dumped on one phase causing wierd imbalances.

It`s still most likely to be an unbalanced lead into a line input or a mike cable fault. Make sure that they aren't using a high impedance mike anywhere.

Ron(UK)

If that`s the case, sometimes, just turning the unit through 90 degrees will reduce the buzz.

Ron(UK)

Yes. It sounds as if the operator is a newbie at this sort of thing - most will be quite used to the tricks of the trade for reducing lighting interference which has been a problem since DC disappeared and solid state dimmers arrived. Or even before that - what were the 'valve' ones - Klyriston?