power supply humming

[turing]

here's a strange little phenomenon - i built a john hollis zombie chorus that sounds great. i lent it to a friend for a gig, and he said it made an unusable hum as soon as he powered it up. i got it back, tried it with my power supply and it's still perfect. got hold of another power supply and sure enough it hums like a mad thing.
my usual supply is putting out almost exactly 9 volts. the new one i test is 11. could this alone be the reason for the humming? i then thought i'd better test it on some of my other boxes, the treble booster, anderton tube fuzz, and apart from the blues breaker, they all do the same thing.......fine with my supply, big humming with the new 11 volt.
both wall warts are nominally rated as 9volt, 300ma. anyone shed any light on this?

[R O Tiree]

Power supplies vary in how much smoothing they do of the rectified output.

Best bet is to get a regulated power supply.

[MarcoMike]

... and if yours puts out "almost exactly 9 volts" I guess it is probably a regulated one.
Non regulated supplies said to be 9V should be able to give you 9V at max load, while the voltage is higher (for instance 11V..) at low loads.

[David]

A member with the handle of jimmy54 had a similar problem not too long ago.  Check out this thread:

http://www.diystompboxes.com/smfforum/index.php?topic=53194.0