As bought from here:
http://www.ebay.co.uk/itm/2917862715...%3AMEBIDX%3AIT
As standard there is a low level hum present, this is cured by fitting an extra capacitor. You need a 470uF 35V electrolytic, the NEGATIVE lead is connected to the junction of two 47 ohm resistors on the top of the board as shown below:
The POSITIVE lead is wrapped around the side of the board and connected to the 0V or 'earth' connection of the input sockets: