Hi All, Newbie with a first post so please be nice

My electronics is a bit rusty having not used it for a few decades - since school but I'm getting there.

I am creating a 'door bell' for a warehouse which requires sound and light notifications and for the signal to be maintained for a loner period than the bell button is pressed. I have 2 separate timer circuits which each switch a relay: 1 powers a strobe LED circuit and it works fine, the second powers a sound generator and an amplifier. The sound generator works fine, as does the amplifier as I have tested them independently. they also work fine when connected one to the other but only when fed by independent power supplies - the generator fed from the Power Rail of the bell unit box and the amp by a separate bench power supply. However when I connect the amp to the Power Rail in the box then it does not work. It is not current drain issue as the amp only pulls 20milliamps max so I am assuming there most be some kind of issue with the sound generator and the amp being on the same power source - does this sound right? and if so, how can I split a 12v feed to provide 2 independent sources - ideally I don't want to have to plug in 2 separate power adaptors.

Thanks.

 

Schematic?

 

First is the schematic of the timer used to switch the power for the sound generator. Second it the schematic of the sound generator and amp.

The +ve 9Vsupply is connected direct to the timer and amp circuits and via the relay (of the timer circuit) to the sound generator -ve are all common.

Hope that helps. Thanks.