Bass Double Box - power supply suggestion...

[Davide]

I've just finished a double fx box for my bass palyer.. an orange squeezer and a bazz fuss in a single enclousure...
The circuit is not yet into the enclosure and testing it i've noticed a thing... with a 9v battery it works great.. but with a simple 9v power supply provided by the bass player himself (originally a cordless telephone pwr supply i think...)... the Fuzz works fine but with some radio stations in my amp...the compressor has a very  loud "hum"....

I think it's probably a not well filtered power supply... but what can i do ? some capacitors between 9v and gnd ?