Amp Kit Hum Problems.

[Meehah]

I am experiencing a hum when using my Champion amp I built from a Jaycar kit. At first it worked perfectly but during use, it developed a hum than is a bit higher than usual pickup hum. It sound quite a bit like the sea except at a constant pitch. Here is the schematic I am using (except without the preamp section). I am using all the components that came with the kit and have resoldered all connections and checked everything thoroughly. Any help would be very much appreciated as I am totally stumped!

[amptramp]

The base of Q1 is floating and that can pick up ambient noise from the /MUTE input.  I would see if a 100K resistor from the base of Q1 or the mute pin did anything.  I am not familiar with the IC's, so I will not hazard a guess about their operation, but operation of the preamp from 5 VDC seems a bit low unless the dynamic range is rail-to-rail on the input and output.

[Meehah]

But would this explain it working without hum for a few days then suddenly after plugging it in again, it starts to hum? I was using it with no problems through a speaker, then I unplugged it, went and got some headphones, and when I got back the hum was there. Excuse my lack of electronics knowledge.