I have a voice chip with a sound I want to play, the output is 200-400 mv. Its running into a TI LM4950 7.5 watt audio amplifier chip. Sound is clean but volume is low. The finished product needs to have a fixed audio output of 85db. I started to put in an old 741 op amp and then realized it typically uses a bipolar power supply and I just have +12 vdc. Any recommendations?