Use of LM386 with simple regen receiver

Question

I have been experimenting with a very simple AM regenerative receiver discussed at circuitbasics.com. The schematic is shown here:

I obtain fairly good performance feeding the output to an old Radio Shack amplified speaker. I'd like to build an audio amplifier based on an LM386 op amp as part of the circuit, such as is shown in the same article, for a crystal receiver (see partial schematic below).

My question is this - would the impedance match (radio output to LM386 amp input), and would an LM386 amplifier be suitable for driving a small speaker or 8 ohm earphones? Can someone suggest a schematic for such an amplifier to use with this circuit?

Answer 1

Reading the data sheet definitely indicates that an \$8 \Omega \$ is within its specification. Follow the guidelines in the data sheet.

The input resistance for the LM386 is 50K. This in parallel with the 10k potentiometer drops the input to as low as 6.3k which will definitely load the collector of the receiver by about ~50%, maybe less. If that gives adequate volume without distortion then you can use it. The only concern is the excess load may lead to collector clipping.

You can buffer the receiver output with an op-amp to eliminate loading. If you want old school, a capacitively coupled emitter follower stage between the receiver and the LM386 would also eliminate loading.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 2

Usually a "regen" radio is overloaded by strong local stations but does not have enough gain to hear weak distant stations. A normal superhet radio has automatic gain control to prevent these problems.

I am only 77 years old so I was not old enough to make a 62 years old regen AM radio. Instead I made a superhet AM radio that worked fine but sounded so bad that I made an FM radio from a kit that worked well and sounded perfect.