TDA2003 just gets hot and crackly [SOLVED]

[midnightblack]

Hi. Firstly, I'm new to this forum, so hi . Although I've been visiting this forum over the past few months, now is when I made an account.

Problem at hand. I'm making my first guitar amplifier. The problem lies, in the output stage, between a TDA2003 connected to a generic hifi speaker.

Basically, when I turn it on, I can firstly hear all sorta weird fuzzing, increasing in frequency, as though things are charging up (listening to the speaker), I assumed its the caps charging or something (or maybe even the caps inside the computer PSU which I'm using as a power supply for now). After that, it gets pretty clean. Then I connect a source, e.g. my mp3 music player and the output is very weird. When I turn the volume right down, I can hear a faint, but quite good reproduction of the song. But then slightly higher and I hear some portions of the song (loud parts) verrry loudly reproduced, like jumpy crackles, but still having the decent quality faint sound coming in the background which hasn't gotten louder.

The TDA2003 gets hot shortly after I turn on the supply, with or without an audio output. This also seems weird, I have connected a simple small clip on heatsink. It should atleast perform well for a few seconds before it gets hot, no? (if the problem is that the heatsink is not big enough)

I really tried a lotta things and I can't think of any more. This seems like something very simple that I've overlooked because the audio IS being reproduced, but just weirdly. When I turn it up a bit more, the loud parts get extremely loud and it just sounds like a complete mess. However, when I turn up the source riight up, it does seem to somehow be produced better, albeit at very high volumes.

If this is a common symptom from missing out a simple capacitor somewhere, please point it out! I'm pulling my hair out trying to figure this and I don't have an oscilloscope at home!

EDIT: I haven't added much technical details as I think it sounds like a very simply problem (like the time when I didn't realise the significance of decoupling capacitors, simply killing the sound). But here is the circuit diagram which I followed:



UPDATE:

It works! I am not entirely sure what exactly caused it to work, but for anyone looking for answers, here are the list of changes I made:

> Changed the ground connections to star topology. Basically I had each stage's ground connections connected together and finally connected to one central ground. I think this website explains it much better http://www.lh-electric.net/tutorials/gnd_loop.html

> The 100nF in series with the 1ohm resistor on the output side, was also sent to a different ground and not connected to the TDA2003's ground (directly)

> I added a huge ass heatsink, I realised I had an old computer's CPU heatsink lying around and luckily it had screw holes, so I screwed on the TO-220 style package onto a corner of that. Now its cool enough to even touch the chip!

NOTE: I did not add the Capacitor and resistor in parallel in the feedback loop (C3 and R1 in the picture from circuitstoday) and it worked fine for me.

Now to really make it sound nice and learn how to make some decent stompboxes 

[Mark Hammer]

Most of those TDA power-amp chips will want more heat dissipation than you have appeared to provide.  Many of them are thermally coupled to the metal chassis or to sinks that are equipped with a lot of surface area.  Bear in mind that a heat sink of, say, 1-1/2 x 2" with a half dozen fins on it is NOT equal to a single flat piece of aluminum with the same 1-1/2 x 2 footprint.  It is the total surface area that provides an escape route for the heat, not just the perimeter.

[R.G.]

1. Check the input and feedback capacitors for the correct orientation of + and - pins.
2. Use your voltmeter to make sure that there is 0Vdc on the 10K volume pot.

[midnightblack]

Most of those TDA power-amp chips will want more heat dissipation than you have appeared to provide.  Many of them are thermally coupled to the metal chassis or to sinks that are equipped with a lot of surface area.  Bear in mind that a heat sink of, say, 1-1/2 x 2" with a half dozen fins on it is NOT equal to a single flat piece of aluminum with the same 1-1/2 x 2 footprint.  It is the total surface area that provides an escape route for the heat, not just the perimeter.

Thank you for the reply.

Actually what I used that for is not something permanent, I used something simple so that I could try this design. If this works, I am planning to put it inside a case with adequate heat dissappation etc. I am just working with barebones for now.

The question remains though, even though the heatsink may be inadequate, it still seems to make the IC work normally (i.e. within working temperatures), I even tried putting a fan to move a lot of air through the fins of the clip on. However the problem is still there of the output not working as intended.

I've read from the datasheet that this is an AB amplifier. That means there must be very little power loss at 0 input no? Then I'm guessing there's some other reason the chip gets hot even without any input. Any ideas?

EDIT: I've read a fair bit of problems related to oscillation on the chip.

General questions:

What does oscillation sound like? Can high frequency oscillation exist (without us hearing it) alongside hearing normal audio?

[midnightblack]

1. Check the input and feedback capacitors for the correct orientation of + and - pins.
2. Use your voltmeter to make sure that there is 0Vdc on the 10K volume pot.

The caps are the right orientation, I already checked the wiring part of the circuit many times now. This is puzzling 

When you mean check there is 0V DC on the volume pot, which node are you talking about? The "output node" of the pot..?

I initially thought this wouldn't be that hard and now ended up having a very crowded veroboard. I'm going to solder everything from scratch again, onto a more spaced out piece. Will update. 

[midnightblack]

I found this circuit design on www.circuitstoday.com. Can anybody explain to me the significance of C3 and R1? I am asking since the design I used didn't use those two components.

[Digital Larry]

Can anybody explain to me the significance of C3 and R1? I am asking since the design I used didn't use those two components.

C3 and R1 will reduce the gain at higher frequencies by -6dB/octave.  The corner frequency where this starts to become apparent (-3 dB point) is 1/( 2 * pi * R1 * C3).  So that would be:

1.0/(6.283 * 39 * 39 * 10^-9) or about 105 kHz.  Since this is outside of the audible range I'd say it's there to help prevent high frequency oscillation which you might not hear but could fry the chip.

I've assumed that the TDA inputs act like a regular op-amp which might not be a good asssumption.  But the overall topology looks like pin 1 is the (+) input and pin 2 is the (-) input.  Overall pass band gain is set by  (R3 + R2)/R3.