Wednesday, February 6, 2019

building a 2 stage PNP amp - with design data considerations

I want a low Z input and a low Z output. For max power transfer you need Z match, To reduce power loss you want Zgen << Zload. If the generator Z is zero ALL power is sent to the load. If the generator Z is infinite no power is consumed. When Zgen = Zload half the power is consumed in the generator. For this amp I want 50 ohm in and out. So what choices have to be made, what options are there?

So from the chart CB 100k - 500k Rout and CC 150K - 300K Rin. CB 30-1k Rin and CC 1K - 20K Rout.
So a CB feeding a CC would be:
30 ohm in - 100k out feeding 150K in - 1K out.
Loading the previous stage is to be avoided so I listed the low values for each parameter. I want 50 ohm in and out . The 1K out is the only problem. I found some 1300 : 8 ohm transformers for $.70 each so I use one and it all works out.
The circuit is very simple. 2 transistors, 4 resistors, 4 capacitors and 1 transformer.
100uv input will drive my earbud.
The frequency response is flat.
The as built. I took an old battery apart and nailed the connector to the breadboard. Using finish washers and screws allows changing the transistor. The MP40 works well.
With the battery plugged in it is ready to try. I have some V-Caps on order from Peebles Originals. When I get them it will be time for a build.
For the math minded a chart from TI.
I put a speaker on the output and it was easy listening level. I put a high Z headphone across the transformer primary and it was good volume too.

I put a tuner and antenna on it and tried some other transistors. It worked with all I tried but I think the GSS109 output and P416B was the winners. I tuned a station and changed parts. The signal was fading a little so my test could show different results if I tried it again. Some transistors made little difference while others seemed to give a boost.

No comments:

Post a Comment