How to get 74dB by LM386 lm386.gif
LM386 is very popular IC also in Japan. It is used in Radio receiver. The power of it (500mW) is enough for the personaluse. But sometimes, the gain of it (40dB) is not enough. Especially the direct conversion receiver depend on all of its gain on the audio amplifier. And therefore, we must stay sometimes thepre-amplifier before LM386. I will show you the way to get the 74dB only with LM386. Please watch the circuit ! Rf is the feedback control resister. By chanbeing the Rf you can tune the gain of this circuit asfollows.
|Rf (ohm) |gain |
|feedback |dB |
|resister | |
|3.3 |74 |
|10 |70 |
|33 |54 |
|105 |44 |
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Dear Sunamura-san, I like to read your web-site very much, and Irepeated some of your constructions. I especially like your LM386 70 dB AF amplifier which I called =B3the Sunamura amplifier=B2 in our national Ham Magazine. Now, I have some news for you. The otherday I found in our national ham magazine a new type of a rock stable VFO. They did not mention the first inventor, but I will try to find out who it was. It is a =8CColumbus= =B9 egg=B9 and it cansubstitute syntesizers. It uses a CERAMIC RESONATOR, and the frequency can be spread for about 100 kHz. I attach the electric diagram. The chief part s are the Ceramic Resonator CR and the variablecapacitor C1. I used a standard CR for 3.579 kHz which is used as a clock in American digital devices. After a short warm-up, when you turn the capacitor C1 you can change the frequency for about 150 kHz -from 3440 to 3620 kHz. To cover the CW segnment of the 80 mteres band a variable capacitor of 140 pf is enough. And the frequency is rock stable. The capacitors C2 and C3 must have a capacity...