Simple AM receiver

[crivoli]

My question is if I build this simple AM receiver and feed the output to the LM386 using a gain of 50, should the output to the speaker be good quality audio?

I saw the datasheet for the LM386 and it shows an "AM Radio Power Amplifier" schematic, but can I use one of the other setups without having to add the "ferrite bead" etc... ?

AM Receiver:
http://www.electronics-lab.com/projects/rf/006/index.html

LM386 datasheet:
http://cache.national.com/ds/LM/LM386.pdf


Thanks a ton
-crivoli

 

[audioguru2]

Hi Crivoli,
The AM receiver doesn't have an RF filter like ordinary radios have, therefore its output will contain radio frequencies.
The LM386 amplifier has considerable voltage gain at AM radio frequencies which must be filtered out at its input with the RC circuit shown in the datasheet and filtered with the ferrite bead at the output to prevent radio frequencies from being radiated into the radio's input.
AM radio has noise and interference pickup and narrow audio bandwidth which creates poor quality. FM radio is a huge improvement.

 

[crivoli]

Hey Guru Plz Help,

I built the AM receiver circuit and fed the output to the "'AM Radio Power Amplifier" on the LM386 datasheet. I have everything hooked up except I am not using "ferrite beads" on the output of the LM386.

I actually get a Radio Station around 900AM, but the sound is VERY VERY VERY low!!!

I have the IC at a gain of 50 but I have ti put my ear right next to the speaker to hear it. I tried increasing the gain to 200 but no luck.

I tested the voltages given on the AM receiver schematic at the specified transistors and had the same voltage at every spot except Q3 ©... no idea why!!:

Q1 (b) 1.31V 
Q2 (b) 0.71V 
Q2 © 1.34V
Q3 (b) 0.62V
Q3 © 3.87V  <==== I have around .1 V

Is there anything else I can do to increase the volume or to fix Q3 ©????

Thanks man
-crivoli

 

[audioguru2]

Hi Crivoli,
Your Q3 is fully saturated when it should be acting as a linear amplifier.
It is only a transistor, two resistors and two capacitors. Check or replace them and you will see what is wrong.
What transistor part number did you use?

 

[crivoli]

I am using a transistor from a pack of common NPN-Type switching transistors. I do not have the exact model. The are probably like the MPS2222A transistors.

I swapped out the transistor for another one and got the same voltage readings and same results to the speaker.

I will post more on the other site.... thanks