The amplifier internal circuit is:
Which shows several things:
1 The inputs have internal resistors to ground - so external resistors are NOT needed. The inputs are ground referenced. Inputs can be on either terminal, with the unused one grounded, or using a balanced input to both.
2 There is an internal feedback tapped at pins 1 & 8. Leaving these pins open give the smallest gain of about 20, while connecting a capacitor from 1 to 8 increases the gain to 200.
3 An output stabilising network of a series 47nF to 100nF capacitor and a 10 - 22R resistor is highly recommended.
4 To prevent supply line noise or hum reaching the input stages a decoupling capacitor can be connected from pin 7 to ground. 47-100uF would be suitable.
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