AW: (not so) Simple Power Supply Stuff

[Magnus Danielson]

> 
> > And add another 20% to make sure that your gear is still working
> > when the mains voltage drops!
> > A few weeks ago, our power supply company changed, and we had
> > some severe undervoltage in our town. Hey, that's funny if you hear
> > your studio equipment fail one by one!
> 
> This isn't that rare of a problem.  I have power line conditioners on all 
> my studio gear which is set up near an industrial area -- if I get really 
> bored I can hook an AC voltmeter to the mains and watch the needle swing 
> up and down when the factories change shifts!!
> 
> Several designers have also addressed this problem by building their gear 
> with switching power supplies.  One device that had terrible 
> problems with live sound was the Lexicon PCM-70 -- the whole thing would 
> go nuts with the slightest dip at the mains.  They have now corrected 
> this problem by putting a switching supply in the PCM-80.
> 
> Here in the U.S. line voltages vary greatly from place to place.  I've 
> set up gear in places with mains as anemic as 105VAC, or as hot as 
> 125VAC.  One should never assume that the voltage is 115 (or 117) -- 
> especially when designing a power supply.

Well, the nominal voltage is 117 V in US and 230 V in most Eurpean contries.
As line conditions may vary (and total load etc.) the line voltage may vary
within +/- 10 % of the nominal voltage (this is not exactly true, I know that
other sligthly diffrent values really tell the truth, but I don't have them
around). So you can expect such high diffrences in voltage, so should any
power supply do.

Then off course a power supply must be able to survive various kinds of 
disturbances (like voltage dips when bass amplifiers pump (it is nasty to see
when you know that the main is 3 x 64 A 380V... :)), but to a certain level.

For a rig you could go to the extreme of haveing both line conditioners and
PSUs....

To weak/bad powersupplies is a much to common problem... I hate it!

I have also seen the case when an amplifier with switching supply failed to
start unless it was at some 200 V (We usually run 230 V) where as another amp
(same model) would happliy start and would nicely survive down to 100 V.
It showed out to be a component failure... but when it worked it made a very
good impression as to line level stability....

Magnus