It looks like a gain reduction mod, which will definitely reduce hiss. If you want the amp to be even quieter, use a 1W 47K metal film resistor instead of a 1W 47K carbon composition resistor. Not only are metal film resistors tighter tolerance than carbon film, they are also are quieter in operation than carbon film resistors. One can get 1W 47K metal film resistors from Mouser, but shipping costs will make it cheaper to purchase 15 from Amazon.
Set of 15 Pieces 47K Ohm 1 Watt (1W) Metal Film Resistor Tolerance: 1%: Amazon.com: Industrial & Scientific
Set of 15 Pieces 47K Ohm 1 Watt (1W) Metal Film Resistor Tolerance: 1%: Amazon.com: Industrial & Scientific
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