how to choose components value

Thread Starter

warmachine

Joined Jul 24, 2021
6
hello everyone ,
I am new in electronic but enthusiastic i simply want to design a class A amplifier and searched it . but totally confused that "how to choose correct value for components please help me and guide me step by step how to choose.
 

Audioguru again

Joined Oct 21, 2019
3,499
This simple circuit makes a very poor power amplifier to drive a speaker. Even when it is not producing any sounds, the transistor will get extremely hot because the power supply current will always be very high. To keep the heating down then the maximum output power in a speaker will be very low.
 

Thread Starter

warmachine

Joined Jul 24, 2021
6
You use the minimum value from the datasheet.
Hi sir..

Actually i am confused coz somewhere i saw that " we should check beta from multimeter in hfe mode " so is it right way ..?
In this case my multimeter is showing 249 for BC547
 

dl324

Joined Mar 30, 2015
13,078
Actually i am confused coz somewhere i saw that " we should check beta from multimeter in hfe mode " so is it right way ..?
Whoever said that was wrong. We use the minimum value from the manufacturer datasheet. That way the design will work for any BC547.

In this case my multimeter is showing 249 for BC547
That's only valid for the collector current and Vce used by the tester. Otherwise, that number is only good for qualitative comparisons.

110 would be a more reasonable number; unless you're using it in saturation mode:
1627427535764.png

Or use this graph:
1627427613562.png
 

LowQCab

Joined Nov 6, 2012
1,078
The real question is .......
Why would You ever choose a Class-A Amplifier Design ?
No one can detect distortion levels lower than ~1% in a Double-Blind-Test,
and even though a Class-A Amp has no Crossover-Distortion,
it has substantially higher Distortion of other forms.

Your Speakers have over ~10% Distortion, guaranteed,
so what's the point of a Class-A Amp ?

You can get a complete 20-Watt Audio-Amp in a TO-220 5-Pin-Transistor-Package
that has less than 0.015% Distortion.
That's almost 100-times less than any Human can detect,
plus it's around ~70% efficient, instead of (maybe) ~20% like a Class-A Amp.
https://www.digikey.com/en/products/detail/texas-instruments/LM1875T-LF05/3640532

Or, if you'd rather build it yourself, and want more Power ..........
.
.
.
High Power Bridge Amp FLAT .png
 
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