Re: Help with power supply noise., Please. -- Success & Thanks.


I have solved the noise problem and I want to thank all who provided input.
As best I can tell the noise is down to about 600uV P-P and mostly 120Hz. The 50KW AM broadcast transmitter
located close by has a tendency to inject RF into my scope probes which makes for pretty fuzzy traces. The
biggest single difference came when I put a very large bypass cap (2200uf) on the -12V line. I thought that
was a bit strange because the +12v line has considerable noise riding on it that's coming from a brushless 12V
fan and it just barely shows up in the output. The remaining noise does not change under a full 4A load
either. At least I can't see it on my scope. The noise may even get lower once I get everything mounted in a
metal case and shorten the cables to the front panel pots. I picked up some 2 conductor shielded cable at a
hamfest on saturday and using that to connect the pots may help a bit also.

Btw, It concerns me that I can't measure any difference in output voltage between no load and a 4A load. I
used an HP 3478A 5 1/2 digit meter and the 40.000V reading did not change when when I connected my 10 Ohm load
resistor. I wonder what I have unknowingly traded off for such good regulation. I would have guessed it would
be noise and/or instability. I suppose that somewhere down the road I'll find out. It does drift a few
millivolts as it warms up tho. That's probably not helped by having to use the LM6132.

Now to make a gizzmo to switch my load on and off so I can measure the time it takes the thing to respond to
step change in load.

Thanks again.

Mike



"The scientist is possessed by the sense of universal
causation...His religious feeling takes the form of
rapturous amazement at the harmony of natural law,
which reveals the intelligence of such superiority
that, compared with it, systematic thinking and acting
of human beings is an utterly insignificant reflection."
Albert Einstein (theoretical physicist)
.

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