shirriff@sprite.berkeley.edu (Ken Shirriff) (01/07/91)
Several people have asked how I converted the microphone level outputs on my Radio Shack mixer to line outputs. I used a pair of LM386 amplifier chips to boost the low-level output to line-level. The LM386 has the feature of running off a single 9 volt supply. Pinout of LM386: 1 gain 8 gain 2 -in 7 bias pin 3 +in 6 VS 4 gnd 5 Vout Connections: A 1K resistor from pin 1 to pin 8. A .1uF capacitor from pin 2 to the original mixer output (i.e. the output from the PC board that used to go to the output jack.) A 1M resistor from pin 3 to gnd. Connect pin 4 to gnd. A 1uF capacitor from pin 5 to the output jack. Connect pin 6 to the +9V after the power switch. I hooked up one of these for each channel, soldering the parts on the bottom of a single 16 pin socket, which I stuck inside the mixer. The resulting line outputs are somewhat noisy, but they're good enough for me. I included sci.electronics in the newsgroups line in case anyone there can comment on this design or suggest a better way of doing this. I couldn't find the LM386 in my databook and I don't really know what I'm doing, so this design may have problems. Ken Shirriff shirriff@sprite.Berkeley.EDU