AW: (not so) Simple Power Supply Stuff

[Haible_Juergen#Tel2743]

> If 19.3 is the average input voltage, at the bottom of the ripple the
> input voltage will be 19.3 - (4.2/2) = 17.2 volts which is too low for
> the 317.  You will need to approximately double the filter caps to keep
> the input voltage above 18 volts.

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!
First thing was increased hum in my Midiverb - didn't recognize
the reason for this, thought I had made some ground loop.
Then my modular started to behave in strange ways - voltage regulators
were gapping and HF oscillation occured - still didn't think of mains
voltage drop, as the Modular needed a larger xformer anyway, to
supply the increasing number of modules ..
Then My OB-8 went nuts. If you know me, you can guess that was the
point when I stopped thinking this was funny, and called the power
supply company in the middlle of the night (;->)
There were a few other effects (my midi patchbay lost all its memories,
but who cares...), but there was *one* synth that didn't mind it all:
The Prophet V ! This was the first time I started to value the overkill
PSU design of this beast!
While a drop in mains voltage of more than 10% should be the
exception in a home studio, it might not be uncommon in stage
environment with light shows etc., so I'd really go for the next larger
secondary voltage for the xformer.

JH.