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0.5W audio amplifier with TDA7052A

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gzkftw

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Hi guys i need help with my assignment below, i am not sure how to do the transistor switching circuit using the control signal from the remote control simulated using SPDT switches. i have attached the block diagram image to the post. Thank you for you time.

Specifications: to design a 0.5W audio amplifier with music, voice and mute modes. the volume of the output must be adjustable. the design should allow end-user to select "music", "voice" and "mute". the selected choice must be indicated visually using different colored LEDs.

The audio signals ( both voice and music) are sourced from a function generator the level of the base band signal is 200m Vp-p for frequencies rangeing from 10Hz to 20kHz.

The end-user has a choice of selecting "music" or "voice" and "mute" mode. this is to be done via remote control which sends an appropriate control signal to a transistor switching circuit. the control signal from the remote control will be simulated using SPDT switches. the recommended supply votage to the transistor switching circuit is 5V.

ICs: uA741; TDA7052A
Regulators: LM78L05; LM78L08
potentiometers: 10K; 100K; 1M
transistors: 2N2222; 2N3904
 

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When you select an input signal, you want the other signals to either disconnect or shut off. Old-fashioned sound systems had interconnected mechanical switches. Pressing a button caused the other buttons to pop up. You need to do the same thing electronically.

There are logic gates to perform these tasks. A 3-input AND (or NAND) gate comes to mind. Add invert-gates before one or 2 inputs as need (example, so that the output goes High only when input #1 is High, and the other two are Low).

Another trick is pullup/pulldown resistors. These create a default condition at a terminal. To override the condition, apply a signal that comes from a lower impedance. Or sometimes through a diode (oriented in one direction or the other) if you only want for a certain polarity signal to influence the condition.
 
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    gzkftw

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I would use a modern simple Cmos transmission gate to pass the audio signal to one of the three function blocks the but you are supposed top use old fashioned transistors.
A turned on transistor can be a pretty good short circuit to ground so feed the input signal to all three blocks though series resistors and use turned on transistors to short the signal at the input of the function blocks that you do not want.

I disagree with the "voice" filter that cuts important high frequency consonants sounds (25 sounds are in English) in speech. Consonants go up to 14kHz and people do not talk using only vowels.
 
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    gzkftw

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Hi guys, thank you for you reply. i have tired drawing the circuit with you guys suggestion, i cannot remove the filter and have to use the transistor because the assignment state that i have to use it. Please take a look at the circuit i have draw.
pin 4 is the mute sorry that i didn't put it down in the circuit. Thank you for your help.15224737_120300000875017492_784257656_o.jpg
 

You made some mistakes.
If you use a transistor to short the Music or Voice signal to ground then the base of the transistor needs a series current-limiting resistor.
The transistor that shorts the voice signal must short the output of the filter, not its input.
You have nothing to allow one signal to pass since both Music and Voice are connected together. Therefore an audio mixer (use the opamp) can allow a signal to pass when the other signal is shorted.
Your NOR gate does nothing and is not needed anyway. Replace it with a switch to mute the amplifier and pin 4 needs a voltage for the amplifier to be unmuted.
 

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