Power Amplifier

[PWKseeker_127eq]

Good Day to everyone, I'm building a circuit in Ltspice particularly a power amplifier. I'm trying to generate a undistorted (straight) waveform in the simulation, however, I always get different waveforms which are always distorted or have curves.

I need help in generating a straight waveform in every voltage and current component (Ve1, Vc1, Vb1, Vb2, Ve2, Vn001) in the circuit. Can you assist me in where I got wrong in the circuit? Thanks

Ve1, Vc1, Vb1, Vb2, Ve2, Vn001, Vr8, and Vin are the ones I need to obtained an undistorted waveform. Thanks again!

 

[AnalogKid]

Your question is not at all clear. The schematic shows a sine wave source. There is nothing "straight" in a sine wave.

What do you mean by "straight"? What is it you are trying to achieve? What is the amplifier used for? Audio? Video? Servo motor drive? What is the frequency range you need to handle?

1. At a frequency of 0.1 Hz, exactly how much change in the output are you expecting in 1 microsecond, which is one ten-millionth of one cycle?

2. C2,C3, R8 form a high-pass filter with a cutoff frequency of 796 Hz. Assuming the desired output point is across R8 (you don't actually say), this is over 12 ***octaves*** above the input frequency, for an attenuation of over 72 dB. For a high-pass filter attenuation of 1 dB at 0.1 Hz, the total output capacitance has to increase by 16,000x.

3. Why is Q2 in backwards?

4. The input coupling network is another high-pass filter, this one with a cutoff frequency of 159 Hz. Same issues as above, for a total attenuation from input to output of over 132 dB at 0.1 Hz.

5. Seems like a lot of work to go through for a 1 mV signal.

ak

 

[Nigel Goodwin]

Good Day to everyone, I'm building a circuit in Ltspice particularly a power amplifier. I'm trying to generate a undistorted (straight) waveform in the simulation, however, I always get different waveforms which are always distorted or have curves.

Well it's not really a power amplifier at all, only a small part of one, the sort of thing you find in a book to demonstrate a principle, and not an actual working circuit. It's going to perform horribly.

 

[PWKseeker_127eq]

Your question is not at all clear. The schematic shows a sine wave source. There is nothing "straight" in a sine wave.

What do you mean by "straight"? What is it you are trying to achieve? What is the amplifier used for? Audio? Video? Servo motor drive? What is the frequency range you need to handle?

1. At a frequency of 0.1 Hz, exactly how much change in the output are you expecting in 1 microsecond, which is one ten-millionth of one cycle?

2. C2,C3, R8 form a high-pass filter with a cutoff frequency of 796 Hz. Assuming the desired output point is across R8 (you don't actually say), this is over 12 ***octaves*** above the input frequency, for an attenuation of over 72 dB. For a high-pass filter attenuation of 1 dB at 0.1 Hz, the total output capacitance has to increase by 16,000x.

3. Why is Q2 in backwards?

4. The input coupling network is another high-pass filter, this one with a cutoff frequency of 159 Hz. Same issues as above, for a total attenuation from input to output of over 132 dB at 0.1 Hz.

5. Seems like a lot of work to go through for a 1 mV signal.

ak

Thanks for the helpful feedback.

My bad in the "straight waveform" part. It should be undistorted.

Thankss for the feedback, I have, more or less, an idea of why my simulation isn't running the way I intended.

 

[AnalogKid]

Is this classwork, a work project, a home project - ?

ak

 

[audioguru]

Of course it is homework.
The PNP transistor is backwards, the frequency is way too low, the input level is also way too low, the resistor values are way too high and the capacitor values are much too small. I fixed some of its problems:

 

[KeepItSimpleStupid]

R2 and R3 are better as diodes. How is a 500 ohm source going to drive anything lower in resistance, like 100 ohms?

 

[audioguru]

The original simulation would not run because it did not know if it should do the SINE or do the DC. It cannot do both at the same time.
The frequency was 0.1Hz (one fullwave every 10 seconds). The input signal level was only 1mV peak.
I simulated it at 100Hz and an input of 1V peak with the PNP transistor connected backwards and its performance was the same with a voltage loss of 36.4 times. .