Friday, February 22, 2019

another attempt at a low power low Z amp

The transistor output Z is to high to feed a speaker or headphone. One way to overcome this is to raise the collector current. A higher current will reduce the output Z but it cost power. I want a battery powered set that will not drain the battery to quickly. A BF2040 stage will feed a 50 Ohm load with 10ma current drain. I want to try and do a little better than that. We could use an output transformer but I want to use parts available off the shelf. While winding a transformer is not extremely difficult is not beginner level. I need 1 mv to drive my earbud. This circuit works faily well.
Driving it with 25uv gives me the 1mv out.
100uv gives  over 4mv. So far it looks good but what about the power drain?
1.5ma current drain at 9 volts is not bad. This could be my circuit for my new radio build.
It drives my earbud with the output set to min on my AF generator. I connected a speaker to it and could hear the tone across the room with the generator on about 5%.

My favorite hearing aid amp is very good but it requires transformers.
This one works well. I have some transformer in the parts been that work in it. If you don't have any transformers and don't care to wind any the circuit above is a good alternative.

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