Having come back to the electronics hobby after several years I have recently been experimenting with basic radio receivers. Having had mixed success
With crystal set type circuits I have also built a couple of basic two transistor receivers from circuits found on the web. These work fairly well and drive crystal type ear phones.
However the most promising results have come from an OpAmp design found on “Arrons Home Page” site.
The receiver is made with LM 1458 dual Op Amp, using one element for the receiver and the other for a basic amp.
I would like advice on any simple circuits that would improve sensitivity, selectivity and audio output.
I have tried several audio amp circuits both op amp and Darlington types but they all seem to suffer from distortion and severe “motor boating” noise.

Cheers
Deege.

 

Welcome to AAC!

There are much better op amps out there, the 1541 has some severe deficits that will show up with audio. Something like a TL082 is much better for a op amp. There is also a chip called a LM386 that is a good audio amp, but it is a bit picky. We have had other posts that are somewhat similar.

 

The very simple Opamp Radio has pin 3 (+) input of the very old 741 opamp connected to ground where it will not work properly. The very old 741 or your very old LM1458 opamp needs a negative supply added to pin 4 when the (+) input connects to ground.

AM radios receive amplitude fluctuations from the signal and from interference. The volume heard from an AM radio depends on the signal strength so all AM radios have automatic-gain-control so that the volume does not change between a strong local station and a weak distant station.
The Opamp radio does not have AGC.