I have a circuit which takes a 15VDC supply from a wall adapter.
Most connections are made by shielded cables and I have employed the manufacturer's (and others) recommendations for hum reduction.
Is it possible to insert a 60-cycle notch filter or other high-pass that'll attenuate the hum?

 

No typical if using a DC coil relay?
Have established exactly where the source of the 60/120 Hz is coming from?
Few more facts as to circuit & components used would help?

 

I am going to assume that you are amplifying a low level audio signal.
60 Hz line hum is a nasty critter to eliminate.

Firstly, you need to have a clean DC supply. Remember, your full-wave rectification will give 120 Hz, not 60 Hz.

Secondly, the first pre-amplifier stage needs an extra clean DC supply. Hence you need to take the first supply output and filter it even more for the pre-amplifier.

 

Very often small wall-mounted power supply devices provide very poor filtering, and sometimes no filtering at all.
With no description at all of the circuit I will not even present a guess, other than a lack of adequate filtering of the DC supply.

 

It may also be that whatever load you are powering draws more current than the wall wart supply is able to provide. Keep in mind that any filtering in the supply is the minimum possible to meet the ripple specification for the intended application. So additional filtering is usually required. And check the current listed on the device label, and do not exceed it.

 

thank you. i've gotten an old SOLA linear PS which will hopefully solve this.