Use of Switch mode Power Supplies with audio equipment.

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If anyone might be feeling tempted by low prices and impressive specs from Switch mode power supplies (also called switching supplies and SMPS) -

Read this article first:

http://sound.westhost.com/articles/external-psu.htm

Note that the article is actually about a proposed change to Australian legislation to outlaw external linear PSUs, but the information is still important from a non-legal standpoint.

There are significant dangers not only in terms of increased audio noise and confused digital signals, but in terms of destruction of electronic equipment, PARTICULARY equipment which PLUGS INTO or otherwise ATTACHES to OTHER EQUIPMENT.

Sorry to "shout" but this is really important, and I would (if I may) call it required reading for any midiboxer.

[cimo]

i was definetely going to use a smps for my MBLC, i tested it and it seems to work fine (well my 74165s burned out actually...) so i am wondering and asking if audio equipment is more prone to be affected because of the noise introduced.

simone

[DavidBanner]

I know for a fact that switch mode psu can be used on top end amps and be a dream to run, no ill effects to other equip.

It's all down to the PSU design, which is a bit of a black art apparently.

I think the big problem we are facing here with switch mode psu is that they are not designed for audio, hence the nightmares I've had with my laptop psu....

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The biggest problem is the trade off between safety and EMI.

In order to meet certain EMI restrictions, many new designs of SMPS have a pair of class Y1 capacitors connected between the mains line and the output, as a form of EMI suppression.

These caps essentially mean that the output "floats" about halfway between ground potential and your mains voltage. This in itself is not a big concern, as even an AC transformer will have a floating output, but there is potential for these caps to develop a charge as you plug in (plugging in thus un-floats the output) and increase the output-to-ground potential yet further, to around the peak-to-peak voltage at your mains line.

I should stress here that this is not considered to be a hazard to humans, as the amount of energy available is probably not enough to kill you (although it does hurt - a lot). The amount of energy available will easily destroy, for example, your DIN boards, probably your SIDs (by plugging external devices into the inputs), potentially your core (if say, AINs were connected to a device with a seperate supply).

I should also stress that I am not trying to start a panic here.

I just think we should be a little careful, especially regarding super-super-cheap SMPS-s.