EXC/RX/AF- 01. RX Audio Amplifier

The Receiver Audio amplifier is built off the LM386 IC.

R57 is marked as 220K on the schematic by mistake. It should be 22K.

Components :

1. 10 Ohms - 2
2. 220 Ohms -  1
3. 22K Ohms - 1
4. 3.3K Ohms - 1
5. 4.7K Ohms - 2
6. 10K Potentiometer - 1
7. .1uF (100nF) - 1
8. 0001uF (1nF) - 1
9. 1uF (Tantalum) - 2
10. 10uF (Tantalum)-1
11. 22nF - 1
12. 220uF (electrolytic) - 1
13. 47uF (Tantalum) - 1
14. 1N4148 - 1
15. 2N3904 - 2
16. LM386 - 1
17. 2 Pin Conn - 1
18. 3 Pin Conn - 1

Install all passives first, followed by the diode, transistors and the IC.

Solder the connectors for the speakers and the Vol. Control. Refer to the schematic for the correct wiring! Center pin of the PCB connector does NOT attach to the Wiper! Short SJ5 on the PCB as we haven't built the AGC yet.

Solder wires to the Ground and V+ (Rx).

Double check your board for shorts, slivers etc, and apply power to the board. Carefully touch pin 3 with tweezers. There should be a buzzing/squealing sound on the speaker. The same buzz should be heard on the potentiometer center (Wiper) pin.

If all is working well, you should see these voltages

1. Pin 6 of LM386 : 
2. Collector Q18 :
3. Collector Q19 :

I used a mix of 1206 and 0805 SMD resistors and capacitors throughout the build. As you can see, there arent any tantalum capacitors! Shelfkey and Sunrom were out of stock when I ordered the parts!

A word of warning to those embarking on this build: Watch those connectors! Even though I got the pin pitch right, the plastic shell of the connectors were a pain as they kept budging against the next conenctor. I had to loose the plastic shell of the AF gain control connector so that I could insert the speaker connector properly in place! A dry fit would have saved me the headache!