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Simple AM receiver

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crivoli

New Member
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:
https://www.electronics-lab.com/projects/rf/006/index.html

LM386 datasheet:
https://www.electro-tech-online.com/custompdfs/2006/05/LM386-3.pdf


Thanks a ton
-crivoli
 

Nigel Goodwin

Super Moderator
Most Helpful Member
crivoli said:
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... ?

Well you don't get 'good quality audio' from AM, but using the LM386 will give the quality you expect from AM radio. Depending on the output level from the radio section you might not need as much gain? - and don't worry about ferrite beads!.
 

ronwer

New Member
Why don't you use a MK484 instead? This replacement for the ZN414 should be easily obtainable from a local source. In Holland you can buy from:

**broken link removed**

No doubt that a supplier in your own country has some in stock, even though it's a discontinued component.

Ronald
Norway
 

crivoli

New Member
Hey Guys 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.

Is there anything else I can do to increase the volume?Huh

Thanks man
-crivoli
 

audioguru

Well-Known Member
Most Helpful Member
You forgot to say that the collector voltage of your receiver's Q3 is way too low, like you said on the other web-forum. It should be easy to fix.

The "radio" is a very poor design. Its text says it is a regenerative receiver. Regenerative uses positive AC feedback. This "radio" has negative DC feedback and doesn't have an AM detector nor an RF filter.
 

audioguru

Well-Known Member
Most Helpful Member
Hi Nigel,
The LM386 IC amp has plenty of gain at AM radio RF frequencies. The ferrite bead on the output wire and twisting the wires etc stops it from radiating RF back to the radio's input.
 

crivoli

New Member
Guru,

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.

You say the design uses positive AC feedback but the radio gives of negative DC feedback. Is there any simple way to fix this? I get a weak signal, I just need it to be louder.

Do you have a schematic for another AM receiver you would suggest?


thanks again
 

audioguru

Well-Known Member
Most Helpful Member
crivoli said:
Do you have a schematic for another AM receiver you would suggest?
I stopped listening to the very poor sound quality of AM radio in about 1960 when I heard the fantastic excellent sound quality of FM radio.
AM radio is garbage! Static, interference, narrow audio bandwidth and very high distortion.
 

Hero999

Banned
But FM reception can be very poor in some areas and give even worse quality than AM, also some stations only broadcast on AM.
 

crivoli

New Member
I agree that AM radio is not as good as FM, but the fact of the matter is that I am building an AM receiver, not FM receiver.

Can you help me with the questions I asked before?

Thanks
 

audioguru

Well-Known Member
Most Helpful Member
Hi Crivoli,
If you fix the "Q3 is saturated" problem in the lousy AM receiver circuit you have, then it might work a little better than now.
The collector voltage of Q3 will be about 0.1V if the collector resistor's value is much higher than 10k, or if the 560k resistor to its base connects to +9V instead of to its collector.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
audioguru said:
Hi Nigel,
The LM386 IC amp has plenty of gain at AM radio RF frequencies. The ferrite bead on the output wire and twisting the wires etc stops it from radiating RF back to the radio's input.

You mean under very specific conditions and layouts?, in 99.99% of cases it's not required :)
 
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