audio amplifier using op amp tda2003

[konzen]

hi guys,

this is a simple audio amplifier i am supposed to built for an assignment in uni.
i also have explain how the circuit works. i have identified C1 and C2 as DC blocking capacitors and C3 and C4 function as a voltage regulator but i still can't exactly figure out what C5 and C6 does. after doing some reading and googling i still can't exactly find the purpose of these two capacitors. all i can say now is that C5 is put there to give a frequency dependent feedback. but what is frequency dependent feedback? what is its purpose in an amplifier circuit? i need your expert help. thx a bunch

 

[Nigel Goodwin]

hi guys,

this is a simple audio amplifier i am supposed to built for an assignment in uni.
i also have explain how the circuit works. i have identified C1 and C2 as DC blocking capacitors and C3 and C4 function as a voltage regulator but i still can't exactly figure out what C5 and C6 does. after doing some reading and googling i still can't exactly find the purpose of these two capacitors. all i can say now is that C5 is put there to give a frequency dependent feedback. but what is frequency dependent feedback? what is its purpose in an amplifier circuit? i need your expert help. thx a bunch

C4 and R5 form a 'zobel network', try googling for it!.

C5 is to give AC negative feedback, and block DC feedback, in order to set the AC gain of the amplifier - the DC gain of the amplifier needs to be only one times, for DC stability.

C3 and C4 are NOT regulators, a capacitor can't perform that function, they are supply decoupling capacitors - essentially they make the positive and ground rails be the same AC potential (an essential point in almost every electronic circuit).

 

[konzen]

thanks alot man. but for the zobel network did you mean C6 and R4? anyway thanks again. you've helped me start research in the right direction.

 

[Nigel Goodwin]

thanks alot man. but for the zobel network did you mean C6 and R4? anyway thanks again. you've helped me start research in the right direction.

Sorry, yes, C6 and R4

 

[audioguru]

A TDA2003 is an audio power amplifier, not an opamp. It has DC biasing parts inside for its inputs that an opamp doesn't have, and it has a huge amount of output current capability, much more than an opamp.

 

[konzen]

oh alrite thx guys.

 

[konzen]

guys, i've tried building the circuit on a breadboard. to analyse the output signal i connected the output to a CRO. using a function generator i put in a 20kHz pure sine wave into the input. i keep getting a flatline as my output. this is driving me nuts. i also connected the amplifier to a DC source as supply voltage. i have checked all pin connections but i still cant seem to get an output. i even tried using another amplifier(i bought myself 2). any help is much appreciated.

 

[Nigel Goodwin]

guys, i've tried building the circuit on a breadboard. to analyse the output signal i connected the output to a CRO. using a function generator i put in a 20kHz pure sine wave into the input. i keep getting a flatline as my output. this is driving me nuts. i also connected the amplifier to a DC source as supply voltage. i have checked all pin connections but i still cant seem to get an output. i even tried using another amplifier(i bought myself 2). any help is much appreciated.

For a start don't use 20KHz, audio testing is normally done at 1KHz, not much point testing above most peoples hearing.

These 5 pin amplifier IC's are very critical about layout, I suspect using a breadboard probably isn't a good idea?, although I would expect instability rather than no action at all.

Have you checked all the voltages around the IC?.

 

[konzen]

ok 1 kHz. what do you mean by layout? as in the pin configurations? i did not have time to do that in the lab session just now but i think i'll try it tomorrow. will update. thx lots

 

[Nigel Goodwin]

ok 1 kHz. what do you mean by layout? as in the pin configurations? i did not have time to do that in the lab session just now but i think i'll try it tomorrow. will update. thx lots

By layout I mean the actual connections on the PCB to the chip, they are critical on these types of chips, a breadboard is the worst possible method to try and make one work. Most datasheets give a suggested layout to avoid problems.

 

[JimB]

Things to consider when debugging the circuit.

Is it built/wired correctly?
Are all the components the correct values? Are any of the components faulty?
Is the IC getting very hot?
What is the supply current? How does it compare with the quiescent current stated on the data sheet?
What is the DC voltage at the IC output pin? At a quick guess it should be about half the supply voltage.
Are you listening to the output with a speaker or just relying on the 'scope? What do you hear, any clicks or thumps at switch on/off, anything?
And the oscilloscope! Is it set up correctly?
Are you looking at the correct trace of a 2 channel scope?
Is the input attenuator set correctly?
Is the input coupling set correctly?

JimB

 

[konzen]

hi guys, here's an update. i got my circuit to work. apparently one of the capacitors were connected wrongly. anyway i tested it again with the signal generator and osciloscope. even though i injected a sine wave i got something like a half wave rectified square wave and the gain looks roughly about 1. i then checked the voltage drop at the input resistor(parallel to amp) and output voltage and got a 40 voltage gain. but when i put a speaker at the output, the circuit amplifies very nicely. even when the DC voltage is only 2 V the sound produced is very loud. anyway soon im gonna create a jack to plug into my mp3 player to check the sound quality. on monday i'm gonna test the circuit with ELVIS. much easier to use compare to the oscilocope. anyway any advice at this point?

 

[Dr.EM]

The circuit must just need a suitable load to function properly.

 

[konzen]

are you implying that the speaker must be there for the circuit to function properly? this means i have to analyse the circuit with the speaker in place? my lab session is on tuesday so i'll test it then. hopefully i'll have enough time to transfer the circuit to the veroboard too. i'll update on my status then. thanks alot for your help. one more thing, as circuitmaker doesn't have my amplifier(need to analyse the circuit theoretically). i've been looking for the equivalent circuit of the amp but still no luck. not the schematic circuit in the datasheet its just too complex, but an equivalent made of op-amps

 

[audioguru]

The amplifier should work perfectly without a load. Its DC output voltage will probably be high since there won't be anything to charge the output coupling capacitor properly.

 

[konzen]

guys, i have transfered the circuit to a PCB. when i put in a sine wave signal the output is fine(i can hear frequency variations as i played around with the frequency) but when i tried to put in an audio jack into my mp3 player and tried to listen to the output, i cant hear anything except for a low frequency rumble. any help?

 

[Nigel Goodwin]

guys, i have transfered the circuit to a PCB. when i put in a sine wave signal the output is fine(i can hear frequency variations as i played around with the frequency) but when i tried to put in an audio jack into my mp3 player and tried to listen to the output, i cant hear anything except for a low frequency rumble. any help?

Post the circuit you've built (with values) and a picture of your completed board.

 

[konzen]

alrite here you go. abit blur though

 

[audioguru]

Your "high quality and very powerful" tiny speaker won't last long if you ever get the amplifier working properly.

 

[konzen]

i see. how big must my speaker be? this is a 2 inch one i think