LM373 Audio Amplifier & Microphone Amp


There is nothing magic about the Audio Amp or Microphone Amps. What I use are proven circuits that have been with me for a long time and so they get reused over and over in the various rigs I build. There are those who are quick to email me about the LM386 and that it is noisy and on and on. Well that may very well be true! But for a low cost communications audio they work just fine. For this rig these two amps were built on the same small circuit board which is mounted near the front panel so wiring to the panel mounted controls and connectors is kept to a mimimum. [You will note the schematic is labeled Simpleceiver --it was used on that project too.]

The input connection is routed from Pin 7 on the TO-5 Style LM373. That is not the same pin as the 14 Pin Dip and that would be Pin 9. The source voltage is 11 VDC taken from the "R" TIP32C Solid State Switch. Refer to the Magic Decoder Ring for the TO-5/14 PIN Dip pinout information.


Audio Amp Stage


Microphone Amplifier

Next we have the microphone amp and this stage was originally developed for use with the LBS II transceiver that I built in 2015. In the case the source voltage is connected to the 11 VDC "T" TIP32C Solid State Switch. This amp perks up at 300 Hz and is capable of 25 dB gain. Lots of punch in a small package.