A basic inverting amplifier using the LM358 opamp. Gain is determined by R4/R1 (or R8/R5). A gain of 1000 sounds high, but experimental testing indicated that it didn't cause saturation of the audio ADC or opamp.

Generally the LM358 is not used in audio applications, but it was the only opamp that I could find locally that only required a +5V power supply.