What kind of dimmer switch do I need for a low voltage light having a toroidal transformer?

I have been sold 2 switches from so called experts neither of which has worked - one caused the light to flicker the other had a horrendous buzzing noise

Public Comments

1. must be a low voltage dimmer switch (over double the price of normal ones) check with your supplier but should be "400W lv dimmer
2. You need to match the load you have connected to the dimmer switch. Dimmer switches have a current rating in amps. I suggest you use at least 1.5 X your load.