9 volt version of AF amp

 When I built this circuit I had a 6 volt lantern battery that was needing using. I tried a 9 volt battery to compare results. My earbud is rated at 1ma and it puts out 1ma with 100uv signal. Looks like this one is a keeper?

 

 

Let's take a look at the Z transformation. Insert a resistor in series with the input and load. When the voltage drop across the resistor is one half the input the resistor equals the input Z.

 So Zin is 500 ohms and Zout is 64 ohms.

If you need an output transformer for your next build it may be worth a try.

 You could use a 2N3906. I use  the 2N5401 because I have a drawer full of them. 

 What would happen if we change the base resistor?

 

 

One stage headphone Amp

Z matching vs neutralizing

3 stage amp with filter and feedback

This little 3 stage amp works really well in sim. R4 and R5 form a voltage divider for the degenerative feedback. They could be replaced with a pot or rheostat for volume control. C2 could feed  a low Z speaker or headset. The input PI network is a low pass filter which should keep RF out of the amp. 

* I built this one and it passes the finger buzz test.  

The old world way of doing it. Based on the formulas posted earlier.

RF Amp and antenna input circuit

The input should be matched to the antenna and the amp input. I will use a bandpass filter for 80 meters. First the page from the book.

and the results.

The sweep.