[sdiy] Multiple Voltage Power Supply / design problem!

[Scott Gravenhorst]

"Paul Perry" <pfperry at melbpc.org.au> wrote:
>..thanks to careful regulation on the audio card itself, or inside the chip
>doing the audio processing!
>Believe me, the old computer PSU isn't the way I'd go.
>
>By the way, anyone looked at a scope trace of the mains lately? It isn't a
>sine wave any more, more like the Matterhorn with the tip chopped off,
>thanks to all the switch mode supplies hanging off it. Oh, and I wonder
>where those mains frequency spikes come from??

I read that when many switching computer supplies are plugged into a circuit, they tend
to synchronize their demand.  The article I read said that 9th harmonic generation was
common, though I can't remember why that is.  I remember scoping power in an area with
weird intermittent computer problems and I saw a sine with a 9F sine riding on it.  when
we lightened the load on the circuit, the problem abated.

I do agree that a computer switching PSU is not that way to start out building a supply
for something like a synth.  Digital circuits have noise immunity that tolerates them. 
  I believe this has been discussed here before, and while anything is possible if you
go to great enough lengths, it seems a transformer, rectifier and linear regulators are
best/simplest for nice clean power for analog circuits.  Dealing with 60Hz is one thing,
but adding RF harmonics _generated_ by the power supply makes things much less fun IMO.

>Paul perry Melbourne Australia
>
>
>-----Original Message-----
>>I wasn't even thinking about putting a linear regulator on the end.
>>More along the lines of some inductors and capacitors.  Must be possible
>>to get reasonably clean DC from a PC PSU.  Plenty of PC audio equipment
>>manages very low SNR, much lower than your average synth.
>
>
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-- ScottG

---------------------------------------------------------

-- Scott Gravenhorst
-- GateMan I - Xilinx Spartan-3E Based MIDI Synthesizer
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