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Some years ago I designed a descrete FM radio which at the time I sold as a kit, which gave a respectable performance and thought it would make an interesting post.
In the next post I will give all the details of the original kit.
Props to Larry for introducing this chip - I had not heard of it before.
The performance is considerably better than I had expected.
A couple of clips are attached - one a local FM station, the other WRMI Miami - with a clip lead for an antenna .....
The headphone output is driving the simple vacuum tube amplifier described in another thread here on the Radioboard.
I'll fill in some of the details on my build in some subsequent posts.
73,
Some time ago I posted details on Making variable capacitors. Unfortunately these were deleted due to hacks.
I will upload what I have (mainly photos) of the original posts and go from there.
I get good performance from this circuit. I chose mechanical regen control because variable resistors have tracks that are open to the air and the actual resistance drifts around a lot. A disadvantage of taking the signal from the emitters of the differential pair is you need a great amount of audio gain. I have used the circuit with an LM386 in gain boost mode (x200). I had to use a separate battery for the LM386 to avoid audio oscillation. However the performance of the radio is very good.
There is another version here: https://sites.google.com/view/analogelectronics/home/experimenters-regen
I would be inclined to use a volume limiting circuit with a superregen to avoid high level ultrasonic noise that you would not be aware of. You would just need to add another 1k resistor and an LED to your circuit.
I actually want to experiment down in the AM band. I will maybe order some parts next month including a 78L05. Keeping RF out of the audio chain gets very tricky at those lower frequencies. Obviously if you use a LM386 for everything like in some of your circuits the issue goes away.
You can create a free website using Google Sites. Google don't advertise it a lot, but it is available and free. It is an option to put some of your circuits there. I was just experimenting with affiliate marketing, hence my electronics site there.
You can turn the simple differential pair Q multiplier circuit into a super-regen just by connecting a capacitor (maybe 10n or so) from the emitters to ground. The capacitor allows the differential pair to temporarily pull
more current (building up oscillation) until the charge in the capacitor is exhausted and oscillation ceases, in a repeating cycle.
W5jag< I wanted to let you know personally that Wix, the platform we use for RadioBoard, is phasing out the old Forum feature. Starting October 15, 2025, no new posts can be added there, and on March 1, 2026, the Forum will be gone completely.
The good news is that all of our discussions, posts, and members will move over to Wix Groups, so nothing will be lost — it’ll just look a little different. I’ll make sure the transition is smooth and will share updates along the way.
Thanks for being such an important part of the RadioBoard community — I really appreciate your contributions!
Best,Larry