[sdiy] Mains interference

[BrightBoy]

Here's some more practical advice on power systems from Arthur Kelm:

Video: http://mixonline.com/video/mixtv/recording/arthur_kelm_ac_power_grounding/

Inteview: http://mixonline.com/studios/design/mix-interview-arthur-kelm/

Technical Papers: http://www.ground1.com/whitepaper1.htm

Cheers,

Jeff

-----Original Message-----
>From: rburnett at richieburnett.co.uk
>Sent: Mar 28, 2014 8:08 AM
>To: "cheater00 ." <cheater00 at gmail.com>
>Cc: synth-diy <synth-diy at dropmix.xs4all.nl>
>Subject: Re: [sdiy] Mains interference
>
>> Regarding silicon junctions shifting RF into the audio band. Dirty
>> contacts can do that too...
>
>Which is why I advised Tony to check that his earth bonding in the house 
>was up to scratch.  It's good advice to check for poor or corroded audio 
>interconnects too though :-)  A poor screen connection at one end of an 
>audio cable vastly increases susceptibility to RF interference.
>
>> Would an overdose of ferrites and ferrite sleeves be a good general
>> advice for studio connections and circuit design?
>
>Ferrite common-mode chokes just outside the metal enclosure work wonders 
>for quick-fixing because they stop nasties travelling down the screen of 
>the cable from getting inside the unit.  You often see them on things 
>like VGA/DVI cables and USB cables.
>
>There's lots of other things you can do at the design stage.  For 
>instance chassis grounded connectors are better than PCB mounted ones 
>because any RF current flowing on the screen will be conducted through 
>the metal case rather than flowing through wires and across PCB traces 
>where it can wreak havoc with your circuit.  Where you don't want to 
>connect the shield of an audio connector to the metal case for hum-loop 
>reasons, you can use a low-valued ceramic cap so that it is connected at 
>MHz frequencies but still open at 50/60Hz.  Ground-planes on the PCB are 
>another good idea as they conduct RF currents much better than thin 
>ground traces.  Little surface mount ferrites on the PCB can be 
>effective if they are right up against where the connection comes into 
>the box.  Ideally you don't want the RF getting inside the box though, 
>because it can then capacitively couple to other things.  Finally, 
>small-value ceramic capacitors across input and output cables act like a 
>short circuit at MHz frequencies.  They will take RF currents that 
>arrive at your unit on one conductor and send them packing in the 
>opposite direction on the other conductor.
>
>EMC textbooks have loads of tips like this for building in good 
>performance at the design stage.  Unfortunately, when the products 
>themselves weren't designed as immune as they should be, that leaves us 
>having to play EMC engineer clipping ferrites on the external cables, 
>fitting external mains filters, etc.
>
>-Richie,
>
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