[Noisebridge-discuss] How close do I need to get with amperage?

[Andy Isaacson]

On Thu, Dec 20, 2012 at 07:32:37PM -0500, rachel lyra hospodar wrote:
> I have a piece of audio gear (roland micro cube) that requires 9v & 185 mA
> .  I scored a power supply that supplies 200 mA but am wondering if it's
> safe to use or if it might fry the amp?

With off-the-shelf power supplies you are fine up to at least 2x.  The
reason is, the power supply is designed to reliably run very close to
the rated voltage.  The current is variable depending on the load to
preserve the accuracy of the voltage level.

There is an alternate kind of power supply known as "constant current"
which varies the voltage instead.  The nice "bench" power supply at
Noisebridge can operate in this mode, and there are some kinds of
circuits that need it, for example somebody told me that EL wire
transformers are constant current.

Any commercial power supply that says "9 volts DC, 200 mA" is a constant
voltage supply.

If your load is *really* low, like if you try to use a 2000 mA (2 amp)
supply to power a device that only uses 10 mA, then you might see
problems (voltage variations mostly).  A sufficiently fragile device
might be damaged that way.

-andy