NAD 3020

I have a NAD 3020 that has a loud hum for about 45 seconds when you first turn it on. A youtube says it is two specific caps in the preamp section. A tech replace those 2 plus two more that his scope identified. It sounds great but that initial hum is still there. Is this just a characteristic of this particular NAD ? Anyone?

 

I worked at NAD back then fixing stuff for a while, and the most common failure I saw on the 3020 were the two FETs (Field Effect Transistors) Q509 + Q510 just before the preamp out jacks. They are like switches, and are supposed to close and let the signal through after a short time delay when you first turn the unit on, to avoid just what you are hearing. They're also hooked to the mute button. Often they failed open, killing a channel or two - in your case they apparently failed closed or are being forced closed by the circuit so they don't mute the turn-on thump. Get a schematic (easy to find on the net) and give it back to your guy telling him to look at that section and he'll fix it.