# good day everyone. can plss someone help me to calculate this circuit.

#### agentperry15

Joined May 19, 2023
35
pllss help me to solve for the voltage gain, the input and output impedance, and the power efficiency of this circuit. I'm really struggling understanding this. I'm just 1st year engineering student and I only know basics. plsss help me. thank you

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#### Ian0

Joined Aug 7, 2020
10,276
Do you know how the circuit works?
Do you know which two resistors set the gain?
Do you realise that the power efficiency will depend on the shape of the output waveform?

#### agentperry15

Joined May 19, 2023
35
Do you know how the circuit works?
Do you know which two resistors set the gain?
Do you realise that the power efficiency will depend on the shape of the output waveform?
Honestly sir I don't know how but what I know is that this is a audio amplifier and the RV1 and RV2 is one that control the volume or gain.

#### RoofSheep

Joined Mar 7, 2023
36
Do you know how the circuit works?
Do you know which two resistors set the gain?
Do you realise that the power efficiency will depend on the shape of the output waveform?
In my opinion you would need a lot more knowledge to analyze this circuit in detail.

#### Ian0

Joined Aug 7, 2020
10,276
RV2 would set the volume (not the gain) but only if it were wired correctly. The capacitor is in the wrong place.
You can think of it as an op-amp, with the non-inverting input at the base of Q1 and the inverting input at its emitter.
That should get you a approximate value for the gain.
To get an accurate value, and a value for output impedance, you are going to need the open-loop gain, and calculating that is not trivial (I'd just use SPICE).
Not only do I agree with @RoofSheep , but I think the question is impossible to answer with the information given.

#### agentperry15

Joined May 19, 2023
35
RV2 would set the volume (not the gain) but only if it were wired correctly. The capacitor is in the wrong place.
You can think of it as an op-amp, with the non-inverting input at the base of Q1 and the inverting input at its emitter.
That should get you a approximate value for the gain.
To get an accurate value, and a value for output impedance, you are going to need the open-loop gain, and calculating that is not trivial (I'd just use SPICE).
Not only do I agree with @RoofSheep , but I think the question is impossible to answer with the information given.
I tried to simulate this circuit in proteus and the gain that I get is 30 db. my problem now is that how to calculate it theoretically. i tried to used 60 volts as its input and 0.138 as its output. i use the formula Gain=Vout/Vin and all I get is not close to the simulated value. i don't know what I did wrong. what should I do sir ?

#### Ian0

Joined Aug 7, 2020
10,276
60V is the power supply. Use 1V for the signal input.

#### agentperry15

Joined May 19, 2023
35
60V is the power supply. Use 1V for the signal input.
I tried but the gain is only 0.13. what should i do so i can measure the output voltage correctly?

#### Ian0

Joined Aug 7, 2020
10,276
I tried but the gain is only 0.13. what should i do so i can measure the output voltage correctly?View attachment 294558
As that has a minus sign, it must be a DC voltage. Don't forget you are dealing with an AC amplifier.

#### agentperry15

Joined May 19, 2023
35
i tried to use ac voltmeter but its the same

#### Ian0

Joined Aug 7, 2020
10,276
You need to correct C3. It should be between the wiper of RV2 and the base of Q1. Connect the input signal directly to RV2.

#### agentperry15

Joined May 19, 2023
35
is this correct?

#### agentperry15

Joined May 19, 2023
35
but why is the gain different from the graph? i only get 0.93 db but on graph its 30 db. why is that so?

#### Ian0

Joined Aug 7, 2020
10,276
but why is the gain different from the graph? i only get 0.93 db but on graph its 30 db. why is that so?
I would expect around 30dB. Where do you have the wiper of VR2 set?

#### agentperry15

Joined May 19, 2023
35
the wiper is in max increased
and i only get 0.93 volts. is this right?

#### Ian0

Joined Aug 7, 2020
10,276
the wiper is in max increased View attachment 294562
and i only get 0.93 volts. is this right?
Probably. You have the impedance of the 500nF capacitor (at whatever frequency you are using) in series.

#### agentperry15

Joined May 19, 2023
35
here is the value of the signal generator
should i change something?

#### Ian0

Joined Aug 7, 2020
10,276
Audio circuits are generally assessed at 1kHz (not 1Hz)