I lately built a 10W amplifier using a TDA2003. I used this circuit (though I removed R4 since I didn't have it, C4 is 50n (two 100n's in series) and R1 is 50Ohm (two 100Ohm's parallel)):
Everything worked fine and there was no noise as far as I could hear.
Now, I wanted to be able to switch between two inputs, like this:
This works, but I get a lot of noise now. All wires are shielded, so I concluded the noise arises in the switch and is amplified after that. Is this correct or am I jumping to conclusions?
How can I decrease the noise? I do not want to switch later, after the amplification, that would produce too much heat and consume too much energy since I'd have to amplify two signals of which I'd only use one.