Problem with Audio Amp...

[ormo]

Hi,

I have constructed the stereo circuit that is on the right of page three of this datasheet: http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1523.pdf

My circuit is identical except I have been forced to use polarised caps for all of the 100µF caps (with the positive side always toward the IC).

When I finished it and hooked it up to the audio output of my phone and a set of 8Ω 3W speakers the sound it incredible distorted and it is hard to hear the original song.

Does anyone have any advice?

PS I have not yet added the variable resistors at the inputs.

 

[ormo]

I forgot to mention:

it is all powered from a 9V battery at the moment and all the ground connections are going to it's negative terminal.

 

[ormo]

Ok following advice from a different site I now have it powered from a ≈10V mains converter. I can hear the original tune but there is a very loud buzzing that goes on and off very quickly that is still present when the audio signal is removed (I'm not sure I've put it into words very well there but it sounds somewhat like a machine gun).

 

[Rolf Zetterberg]

The first obvious checks to do,is to check that the output pins are at around half voltage,regardless of what you're driving the IC with.
The machine gun sound might be motorboating, caused by to little capacitance at the +voltage pin,or too long distance between the IC and the cap.

 

[audioguru]

The IC has a voltage gain of 200 to 400. It needs to have a volume control to reduce the input level so that it does not distort.
It needs a good filter capacitor for its supply voltage.

The 100uF capacitors are polarized electrolytic type. You connected yours correctly except pin 14 and pin 3 must be the positive terminal of the capacitors there.

 

[ormo]

The 100uF capacitors are polarized electrolytic type. You connected yours correctly except pin 14 and pin 3 must be the positive terminal of the capacitors there.

I already have all caps with their positive side towards the IC including pins 14 and 3. What size of filter cap and input resistor would you recommend?

 

[audioguru]

The filter capacitor in the mains adapter must be too small. Use 3300uF or 4700uF from pin 16 to ground at the TEA2025B. The adapter must be rated for a current of 1A.

 

[ormo]

I'm going to try it with a 4700uF 16V cap when I can go and buy one in a few days, I'll post and let you know how it goes

 

[ormo]

I've tried re-wiring it with the variable resistors in there and it all seems very loud but with almost no distortion!!

There's still a bit of clipping so I'm still going use a bigger cap off pin 16. I'm looking to add an LED VU meter if anyone has any tips?

 

[audioguru]

Clipping is when the input level to the audio amplifier is too high so the amplifier's output tries to exceed the positive supply and go lower than 0V. The peaks of the waveform are "clipped" or flattened.

Use an LM3915 for an LED VU meter.