The circuit is an audio amplifier tda 2050. I have some problems in this circuit

Question

The circuit is an audio amplifier tda 2050. I have some problems in this circuit, very basic problem

1) one of the circuit schematics a 100nF (C5)capacitor is connected in parallel to a 1mF(C3) capacitor, to give    anoverall value of 1.0001mF: what is the meaning of that ?

2) Analysis the effect of C3 and C5 in the input signal.Analyze the effect of capacitor C2 on the input signal

3)  What is the nominal gain of the circuit in the flat-gain region of the bandwidth?What is the dc (or zero-          frequency) gain? What happens if your remove C4 fromthe feedback loop?What is the role of the RC-filter      associated with R6C6

4)What could I do if I wanted to provide the user with a volume control?

Explanation / Answer

1. All sources and element in a circuit create some form of noise. Since capacitors can block dc, but are only an impedance for ac signals, creating two or more capacitors which short at a certain range of frequencies will greatly reduce noise caused by the source. Thus, less noise entering the system. You'll need to do a frequency response analysis of the capacitors leaving the power supply. Try setting the frequency to >100Hz, then between 100Hz AND 1MHz, and above 1MHz at each capacitor.

2. C2 will have similar effects, and when audio input is initiated at Vin, it will act as a short. It's shown in the audible range of 20-20kHz.

3.your flat gain will be found at ac analysis (idealy, you would look at the ideal op-amp after shorting all capacitors). The same will be true for dc analysis, respectfully (make caps into opens and solve for the output, and it should be 1). However, if you remove C4, your dc gain will be the same for ac gain. This will cause the signal to shift with so much gain, you may have complete signal loss.

Regarding R6C6, this is not a filter. C6 is a capacitor used for noise isolation at higher frequencies. The real filter is R6C7, which is a highpass filter for reducing low-frequency (or pink) noise generated by the amplifier.

4. Volume control can be done via potentiometer.The simplest way is to replace R5 with a pot (say up to 50kOhms). When it shorts, you have unity, and the lowest possible value, and at 50k, the volume is maximized.

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