Power supplies are quite cheap (or free if you have a junk box like mine
handy) ... try a few different ones ...

It may also be worth while making up a separate plus and minus 12 volt
regulated non switch mode power supply for the analogue parts of the
electronics. I do this in computers where I need to get clean audio in and
out.

Mark
----- Original Message -----
From: "Larry Cochrane" 
To: 
Sent: Wednesday, 5 July 2000 18:04
Subject: Re: noisy power supply


> Angel and others having this problem,
>
> I have noticed this problem with some motherboards. This happens on newer
> motherboards that have switching power supplies that place a lot of high
> frequency noise onto the + and/or - 12 volt supply lines. This noise gets
> into the multiplexor chip and op-amp on the A/D card.
>
> About two months ago I started adding two inductors to my A/D card that
> filters out the problem. The modifications are easy too make, but require
> some soldering skills. I will create a web page that documents the changes
> needed to add the inductors if anyone wants to modify their board. Just
> about any small inductor will work as long as the DC resistance is only a
> few ohms. If you don't have a supply of inductors at hand I can send you
> two if you send me
> an envelope with return postage.
>
> If your not into soldering you can send me your A/D board and I will make
> the modifications for free. All I ask is enough money for return postage.
>
> Too see if you are having this problem do the following using SDR.
> Disconnect the 37 pin connector and press the "1" key and then the "C"
key.
> After a few seconds note the minimum / maximum counts from the A/D
> converter. If you have a 16 bit A/D chip and the min/max count is greater
> then +-8 the modification may help. With a 12 bit A/D chip the min/max
> counts should'nt be higher then +-2.
>
> -Larry Cochrane
> Redwood City, PSN
>
> At 11:44 PM 7/4/00 -0500, Angel wrote:
> >
> >Hi,
> >
> >I just got me new computer and much to my chagrin now all four of the
> >traces on SDR are much noisier.  Little spikes, jus ta few counts.  When
I
> turn off the
> >new computer the noise goes away and when turn it on the noise comes
> >back.  Obviously one solution is to not turn on the computer.  Are there
> >any others?
> >
> >
> >Best regards,
> > Angel                            mailto:angel@............
> >
> >
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