The first thing I would like to say is to not give me the solution directly but instead, guide me while I'm trying to design the circuit.
The second thing is that some of you probably already read my previous posts about trying to understand how to design an amplifier.
I think I've come a long way now and I'm ready to finally understand what's going on.
One of the biggest pieces of knowledge that I was missing was that two circuits connected together (output of the first -> input for the second circuit) form a voltage divider, altering the final output. Now I know that the "game" here is to make this fraction \( V_{o} = V_{WithoutLoad} \cdot \frac{Z_{load}}{Z_{load} + Z_{out}} \) as closer to 1 as possible in order to get the final output identical to the output that has been calculated without a load.
The second thing I was missing, was that the capacitors form high-pass filters with the \( V_{thevenin} \) that they "see". So according to the -3db rule I must calculate the capacitance as follows: \( C = \frac{1}{2πfZ_{th}} \) were f the cut of frequency where the high pass filter will allow frequencies above it.
Now to the actual design:
First I must specify the specs of the amplifier:
1) Vcc (dc power supply)
2) Zin (Amplifier input impedance)
3) Zout (Amplifier output impedance)
4) Gain (Voltage gain)
5) Power, let's forget about it for this project since it will be plugged based not battery based.
I think that's about it.
I possess only a power supply of 5.25VoltsDC so we will have to work with it and achieve the best gain possible.
My load device is a speaker with 4Ω.
Question 1) Will this change once my speaker is under voltage?
Problem 1 (Choosing Amplifier Zout): Usually we want a small impedance since a big one will increase the denominator of the voltage divider and make things worse. If my speaker is 4Ω choosing Ζout is problematic!!! Only if Ζout = 0 or close to 0 will give \( V_{o} = V_{WithoutLoad} \cdot \frac{4}{4 + 0} = 1 \). Can I do it? If not what can I do? Can I add a resistor in series with the load to increase the load resistance and make it big?
Problem 2 (Choosing Amplifier Zin): My input device is my smartphone. I know that a common emitter amplifier the way that it is designed (voltage divider at the base) gives a big Zin already. Should I know the impedance of my phone? Do smartphone companies make the jack output in a way that has a small impedance?
4) How do I choose the gain so that it is possible with the DC power supply that I have and make sure it won't burn the transistor? Probably the second one will become clear when choosing the Ic from the load line. Let's say I want the maximum gain I can get with that power supply and the specified input and output loads. How can I determine the maximum gain I can get with the specs I provided?
Thank you for your time.
The second thing is that some of you probably already read my previous posts about trying to understand how to design an amplifier.
I think I've come a long way now and I'm ready to finally understand what's going on.
One of the biggest pieces of knowledge that I was missing was that two circuits connected together (output of the first -> input for the second circuit) form a voltage divider, altering the final output. Now I know that the "game" here is to make this fraction \( V_{o} = V_{WithoutLoad} \cdot \frac{Z_{load}}{Z_{load} + Z_{out}} \) as closer to 1 as possible in order to get the final output identical to the output that has been calculated without a load.
The second thing I was missing, was that the capacitors form high-pass filters with the \( V_{thevenin} \) that they "see". So according to the -3db rule I must calculate the capacitance as follows: \( C = \frac{1}{2πfZ_{th}} \) were f the cut of frequency where the high pass filter will allow frequencies above it.
Now to the actual design:
First I must specify the specs of the amplifier:
1) Vcc (dc power supply)
2) Zin (Amplifier input impedance)
3) Zout (Amplifier output impedance)
4) Gain (Voltage gain)
5) Power, let's forget about it for this project since it will be plugged based not battery based.
I think that's about it.
I possess only a power supply of 5.25VoltsDC so we will have to work with it and achieve the best gain possible.
My load device is a speaker with 4Ω.
Question 1) Will this change once my speaker is under voltage?
Problem 1 (Choosing Amplifier Zout): Usually we want a small impedance since a big one will increase the denominator of the voltage divider and make things worse. If my speaker is 4Ω choosing Ζout is problematic!!! Only if Ζout = 0 or close to 0 will give \( V_{o} = V_{WithoutLoad} \cdot \frac{4}{4 + 0} = 1 \). Can I do it? If not what can I do? Can I add a resistor in series with the load to increase the load resistance and make it big?
Problem 2 (Choosing Amplifier Zin): My input device is my smartphone. I know that a common emitter amplifier the way that it is designed (voltage divider at the base) gives a big Zin already. Should I know the impedance of my phone? Do smartphone companies make the jack output in a way that has a small impedance?
4) How do I choose the gain so that it is possible with the DC power supply that I have and make sure it won't burn the transistor? Probably the second one will become clear when choosing the Ic from the load line. Let's say I want the maximum gain I can get with that power supply and the specified input and output loads. How can I determine the maximum gain I can get with the specs I provided?
Thank you for your time.
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