[sdiy] power supply for casio CZ1000

Ben Bradley ben.pi.bradley at gmail.com
Sun Feb 23 01:41:02 CET 2020


Oh boy, here's another potentially cantankerous topic. I wrote my
answers below, some others might have different opinions.

> Are all switching power supply wallwarts noisy?

No, but there are so many inexpensive things thesedays that it's hard
to tell what might be noisy. I seem to recall a statement here in
recent years that "switching supplies are a lot better (noise wise)
than they used to be." That might even be true on average, and good
brand names and suppliers surely make well-filtered, low noise
switchers thesedays, but you have to know the brand names and such,
else you'll probably get cheap noisy junk.

>Should I use a power
> supply with a transformer instead?

   What you're thinking of is a big, heavy 50/60Hz transformer that
has traditionally been used in "wall warts" and electronic equipment
for many decades (all power supplies use transformers, but switch-mode
power supplies use switch frequencies around 100kHz and up so that
much smaller transformers can be used).  They're usually better than
switching supplies in many ways, but can have their own problems. The
laminations can be loose and cause an audible buzz at the line
frequency. Inexpensive rectifiers are usually slow to switch off, and
when they do they cause a high frequency RF "ringing" that gets into
sensitive circuits and makes an electronic buzz in audio circuits. But
these problems are generally easier to fix than many switching supply
problems.

>Are these transformer power supplies
> called linear?

   in general, yes.

>Are all power supplies that use transformers quieter in
> audio applications?

   In general, yes.
>
> I have a 9V power supply that uses a transformer that has a big enough
> power rating but when I test the output I read 12V. Will this damage my
> synth?

   A meter reading will give an unloaded reading which is usually
higher than the rated output, but it will be closer to rated output
under load. This should be fine.
>
> Can anyone recommend a source for a quiet 9V, 1A wallwart? When I search
> for 9V, 1A regulated power supply all I get are switched supplies.

   Years ago I got the "big heavy" linear wall warts at thrift stores,
but by now they're almost all switchers.

   It's almost the only thing that's made thesedays for a variety of
reasons. They're smaller, lighter, cheaper to make, and due to the
light weight cheaper to ship.They can often be filtered for audio, but
sometimes it's easier to use and filter a 60Hz supply. The market for
60Hz supplies is for the most part too small to justify making them,
though Digikey or Mouser might have a few. Worst case, you can still
order 60Hz transformers, rectifiers, capacitors and possibly regulator
chips and make your own linear supply.

>
> Thanks. JoeF.
>
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