To see this working, head to your live site.

Where to begin?

Why not start by building a small audio amplifier that can be powered by a 9V smoke alarm battery? And before you know, it can easily grow into a radio project!

While there is no shortage of circuit designs out there, this one is quite simple to build, uses no special components other than commonly available resistors, capasitores, and transistors. It is low noise and distortion, and can give comfortable listening levels in a small speaker, around 200mW (it is louder than you think!)

Sensitivity with the components shown is about 20mV. Frequency responce begins to fall off at around 20 kHz by capasitor C3.

Here is the circuit diagram below:

Current consumption is less than 5mA from a 9V smoke alarm battery.

There are several ways to go about building it. Check out ''manhattan style''. It makes it easy to get started. This is how I built the circuit:

Yes, it is ugly! And it is quick. But you could make a pretty printed circuit board if you wanted to.

5 comments

Comments (5)

LarryDee

قبل ٥ أيام

Can you tell me what resistor controls the gain? And are R1 - R2 4.7 K ?

Thanks

coildog

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Replying to

Hi there,

R1 = R2 = 4,7 ohms. They provide some in stage negative feedback to make the output more linear and reduce distortion. They also serve to limit the maximum current in the quite weak output transistors, 2N3904 and 2N3906.

R5 is also providing negative feedback to the first stage, and this one determins most of the gain, together with R3 and R4.

R3 and R4 is in parallell with R6, as viewed from an AC perspective.

So, that means 1,5k parallell to 1,5k = 750 ohms, which is much less than R6. We can then disregard R6 and calculate the gain as 750 divided by R5, which gives a gain of 22,7 which is suitable for a superheterodyne type receiver.

We can add a preamplifier stage to make it much more sensitive, which could be useful for a crystal set or a regen.

I think it is possible to simulate the circuit in Spice, but I'm not that familiar with it.

I measured some currents. Total current drain was 4,3mA, with about 3mA flowing through R3, D1, D2, and R4. About 1,2 mA flowing through the output transistors with no signal input. That should eliminate cross over distortion.

LarryDee

قبل ٥ أيام

Replying to

I'd like to use it on my regen, as a headphone amp. I'm gonna give it a try, thanks

coildog

قبل ٤ أيام

Replying to

Hope it works for you. Fingers crossed!

LarryDee

Mar 10

This is a class AB amp, cool! It would make a great headphone amp. Even stereo would only be 10 ma. Yes, the parts are all still widely available. And it's not ugly.

This person sells Manhattan parts and pads that work great. His products are really cool. (The website is right out of 1996) http://www.qrpme.com/?p=product&id=SD2

Manhattan style is awesome, and it impresses people when you show them, which is very important 😊 Thanks for posting this project !!!