With a 30V supply, the latest circuit produces clipping when the input is 118mV peak which is only 1.4dB more that the spec then the increase cannot be heard.
By correcting the biasing of the 2nd transistor then the clipping begins at 178mV which is an increased level of 3.5dB that is clearly noticeable (more than double the output power).

A while ago I reduced the resistance of the emitter-follower's emitter resistor so that the circuit meets spec, maybe I should have reduced it more and made enough heat to cook something.
Of course the class-A output emitter-follower is still dividing down the undistorted output level that can be fixed by making the emitter-follower operate much hotter.

 

Hi,
The TS has the assignment to design a 3 stage a transistor amplifier, to the specification as posted in post #1, so why do you insist that it has to meet your gain specification in order to be acceptable.?

I should have reduced it more and made enough heat to cook something.

And what is this supposed to mean, when the max power in a component is is approx 126mWatts.?

E

 

By reducing the resistance of the emitter resistor, I made the original design meet the spec.
By correcting the biasing of the 2nd transistor, I made the circuit work better and produce more than double the output power.
When the improvements are explained to the professor then the student is entitled to extra points.

 

When the improvements are explained to the professor then the student is entitled to extra points.

Hi agu,
But it is the student's course work assessment assignment, not yours.

So by posting your version and improvements to the TS's posted circuit, you have possibly enabled the TS to gain extra undeserved credit points for the assignment.

The rule is, we do not give Homework students direct answers to their assignments.

 

I have built the circuit according to my LTSpice simulation but I get a wave that is not correct and the frequency is also way too high. Can anyone give any advice on how to fix it?

 

It is oscillating probably because it is built with a mess of wires on a Mickey Mouse breadboard.
The wires have inductance and the rows of contacts have capacitance changing the amplifier into an oscillator.
Electronic circuits that have gain must be built neat and tidy. The output must be kept away from the input.

I build prototype circuits compactly soldered on stripboard. I plan the parts layout and cut the strips of copper to short lengths so that they are the wiring of a pcb. Only a few very short wires are the remainder of the wiring. Most of my stripboard prototypes were sold as the final product but a few were given to a pcb manufacturing company.

 

Hi GF,
Please post values for the Input frequency & amplitude.
Also, the amplitude of the Vout signal.

A photo-shot of the amplifier layout would help.

Ignore the Mickey Mouse comments, most of us are here to help guide you with the project, not to make you look stupid.

A simple 3 stage transistor can easily be built on bread board and good give results.

E

Your post #85 image looks as though you are over driving at a higher frequency than the design spec.

 

The scope shows 5V per division. 3 divisions is 15V p-p.
The scope's timebase is 100ns per division. 2.75 divisions is 3.637MHz.
The amplifier might be oscillating with no input signal.

 

I have built the following circuit on the breadboard:



The signal generator inputs a 200mV p-p signal. The DC power supply is +-15V.
It works on LTSpice but when measuring the real circuit there is only a gain of 5. What can be the problem?

 

I have built the following circuit on the breadboard:
View attachment 295205
View attachment 295206

The signal generator inputs a 200mV p-p signal. The DC power supply is +-15V.
It works on LTSpice but when measuring the real circuit there is only a gain of 5. What can be the problem?

Please post your .asc sim file so we can take a look.

Also check that you are really using a 200mv input and the frequency is the same (probably use 1kHz).

 

Hi GF.
I assume the gain of 5 is within the defined bandwidth.

The gain of your 2N2222a could be in the order of BF=100.

Try your LTS simulation with a BF=100.
E


BTW: Your layout looks OK, but add some power rails decoupling capacitors 100uF and 100nF on both supply lines.

 

Here is the .asc file

 

Hi GF,
Tried with a 2N2222 BF=100 no apparent change in overall Gain=50
E

 

Hi GF.
I assume the gain of 5 is within the defined bandwidth.

The gain of your 2N2222a could be in the order of BF=100.

Try your LTS simulation with a BF=100.
E


BTW: Your layout looks OK, but add some power rails decoupling capacitors 100uF and 100nF on both supply lines.

View attachment 295208

When changing BF to 100

Hi GF,
Tried with a 2N2222 BF=100 no apparent change in overall Gain=50
EView attachment 295210

Yes I saw the same.

 

Hi GF,
Your component values on the board look OK, but I would double-check their values on this clip ?
E

 

Hi GF.
Could you please confirm how the +V and -V and 0v/Gnd are connected on the bread board.?
E


Added: Check that the 1st stage gives a Gain =10, with a 200mVppk 1kHz sine input

 

It works with this design. Thanks a lot for all the help!

 

hi GF,
Good to hear, well done...

What was the problem.?

E

 

When I calculated the resistor values for a gain of 10 on the first stage I used a 10k load. I switched the 10k with a 2.2k and calculated new resistor values for 10 gain and it worked.

 

Good, you got it to work, BUT: