Hissing - How To Stop It

[Dukesy 0]

A PAT test is unlikely to find anything in relation to this problem, it comes down to the design of the power supply. All a PAT test is likely to find is a breakdown in appliance isolation, wiring faults and disconnected earths.

 

In laymans terms, part of the design in a switch mode power supply contains a high voltage transistor which is switched on/off many times per second - anything from around 50 on / off cycles per second to many thousand times per second. In a cheap unscreened design or one which hasn't been suppressed properly this rapid on/off action can lead to problems with interference (EMI) either going back down the mains or being transmitted as RF interference to nearby audio equipment.

 

If you remember the days when you used to get a loud 'click' from the radio whenever you turned on a lightswitch, or started up a drill then this is basically the type of interference which poor quality, or failing switch mode designs can also produce.

 

In a good power supply design, a lot of the switching components will be screened by a metal shield and there will be components called chokes, suppressors and high voltage capacitors which will smooth out and remove this interference before it has chance to create an issue. However if these components are missing, are of a very cheap quality or are simply failing then the interference can escape and you start getting problems from sensitive audio or radio equipment.

 

Suffice to say, the better quality the effect and the more you pay for it, then the less likely the chances of this occuring.

 

If the interference is mains related, then buying a suppressed trailing socket adaptor like Rob has suggested to 'clean up' the mains and remove any mains bourne interference is a good idea. However if the interference produced is RF based and not mains related, then a socket like this is unlikely to do much.

 

Its also good practice to keep your lighting and audio equipment split on seperate sockets, and plug in just the Audio equipment into a suppressed socket block.

 

If this doesn't cure the problem, then the only solution is to find the component which has failed (or failing) in the power supply inside the effect and replace it, or fit mains rated suppression components onto the mains input side of the power supply PCB. This is usually beyond most DIY'ers and shouldn't be tackled unless you know exactly what you are doing.

[Marble 0]

Thanks for that, it took me a couple of reads to grasp what you were saying (my brain's fault, not your writing) but that was really helpful. Certainly gives me a better idea of the in's and out's of the more technical side... and why the pat test didn't show anything wrong. Hopefully santa will bring me a suppressed trailing socket adaptor which will at least give me the chance to narrow down a few of the faults and excitingly mean that I can no longer blame "black magic" for the strange noises.

[spinner 0]

for mains induced problems a device like this is an idea

 

CLICKY

http://www.lindy.co.uk/lindyshop/pictures/30087xxl.jpg

 

Good suggestion.

 

I found a Tacima CS929 6 Way Mains Conditioner with RF interference filter on Ebay, brand new, for £19.99.

 

It has made a marked difference to the amount of hiss, which is now virtually imperceptible.