Reverse engineering to learn how to design and analysis the circuits

[zesla]

Hello guys,

Recently I decided to start learning how to design almost simple circuits.
Today I came across to an idea, I decided to put the ready circuits here in this thread and kindly ask the engineers and the experts in the field to come and tell for instance why a component is there at that segment of a circuit and especially why the designer has chosen that value for it (the formulas behind it). Most of times I know why a particular component is there in a particular circuit but do not know why the designer has chosen that value for it.
Here we suppose that we have all stuff to design and analysis the circuits (i.e. Scop, function generator and multi meter).
The main purpose of this thread is to improve our knowledge of designing and analysis the circuits.
I kindly demand experts Nigel, Audioguru, Ron.H, MrAl, and all expert engineer to help.

Thanks.

Zesla

 

[zesla]

How to calculte the values of the coupling caps

The first circuit to be analyzed is a simple Audio Amplifier based upon OP-Amps picked from: Audio Amplifier Circuit.
It has 2 caps on its input and its output. The purpose of the designer by putting those caps in series with the input and the output is to pass the AC signal by the capacitor and to block the DC voltage I call them coupling capacitors (right?). It seems to me that the cap and the load resistor compose a filter to block the DC and to allow the AC signal to pass; But Why the designer has chosen a 100uF cap for the output and a 1uF cap for the input? Which formula should be used for those caps at first when designing this circuit? What about measuring or calculating the frequency response of those RC's if needed?

P.S. I know that maybe we do not have several parameters when just look at a circuit to reverse engineering it (for instance the upper and the lower thresholds of the frequency response), but we can make a guess and just tell and use the formula with an almost near parameter to allow the learner to just learn the real formula for the argued segment.

 

[Brevor]

He should use oxygen free monster cable to connect the speaker!

 

[crutschow]

The reason the caps are different value is that the series resistor for the input is 1kΩ and the output is 8Ω. To get similar frequency response the caps need to be different according the the high-pass -3dB roll-off frequency of 1/(2*PI*R*C) of a resistor and capacitor in series.