TDA7294 won't work

[Flashgun]

Hi everyone,
I'm new to the world of creating circuits, and this is my first project. It is an amplifier based on the TDA7294 IC that I built following the instructions and diagrams that I found on this site (click on the mono circuit picture to download all the infos). Basically I just printed the PCB, transferred it on the board with the "ironing" method and etched it with the ferric chloride. Then I drilled the necessary holes (with a 1mm drill) and soldered on the components as showed by the diagrams and the circuit's photo. The only issue I found was that the layout diagram did not match the photo, so I switched the C1 and C2 capacitators values to match the photo. To power-up the circuit I used an old computer PSU connecting two ground wires and the +-12V DC (with a declared output of 19A and 0,8A respectively). I hooked up a working speaker and connected a 3,5mm socket to the line in and used it to connect my ipod as a source. But, after turning on the PSU and the source, the circuit does not work at all. I double-checked the layout of components and the eventuality of dry-soldering but I was not able to figure out the problem. Thanks for whatever help you may give me, and sorry for the stupidity of my questions, but, as I said, I am a total newbie in this field.

Here are some pictures of the circuit I made, there I removed to IC to verify if it was malfunctioning, but, while desoldering it, few tracks ruined, so I made a new board on which I will solder the components following any suggestions you may give me.


P.S:Sorry for my bad grammar, I'm from Italy.

[sregor]

First question - what voltages on the power supply when you tried to run it? AFAIK, computer power supplies don't work right, unless there is some kind of load on the volt rail, but they do vary. So, try loading it with something, like a light bulb or resistor.
Second - are you running it with a heatsink? Heatsinks make the chip happier, but must isolate the metal tab on the 7294, as this is connected to the negative supply voltage pin.
Third - are you using the right connection and voltages on the muting pin - I don't have the datasheet, but some people have had that problem.

[Flashgun]

Originally Posted by sregor

First question - what voltages on the power supply when you tried to run it? AFAIK, computer power supplies don't work right, unless there is some kind of load on the volt rail, but they do vary. So, try loading it with something, like a light bulb or resistor.
Second - are you running it with a heatsink? Heatsinks make the chip happier, but must isolate the metal tab on the 7294, as this is connected to the negative supply voltage pin.
Third - are you using the right connection and voltages on the muting pin - I don't have the datasheet, but some people have had that problem.

First of all, thanks for your help!
I measured the voltage on the rails with a voltmeter before connecting the PSU to the board and it was stable at around +-12V. The mute function, as declared by the schematic creator, is turned on by connecting a 12V tension to the mute pins, so, when the pins are not connected, it should not be activated. I do have an heatsink, but I have not mounted it yet, what could I use to insulate the metal tab?Again, thanks for your help.
Here I uploaded all of the project info, hoping they will be useful.

[kroto]

Originally Posted by Flashgun

The mute function, as declared by the schematic creator, is turned on by connecting a 12V tension to the mute pins, so, when the pins are not connected, it should not be activated.

is it an Italian site?? I don't know what they sayin'...
^_^

not sure how the mute function inside the IC works (Normaly Open / Normaly Close switch)
but my TDA's, when the pins are not connected to the supply pin, the amp wont play nothin'... it's muted.

[Flashgun]

Originally Posted by kroto

is it an Italian site?? I don't know what they sayin'...
^_^

not sure how the mute function inside the IC works (Normaly Open / Normaly Close switch)
but my TDA's, when the pins are not connected to the supply pin, the amp wont play nothin'... it's muted.

Yes, it is in italian :P anyway, it is also written on the schematic here that when you connect a 12V tension to the mute pins, the function will turn on, otherwise it will stay off. I can't explain it any better than this, because I don't fully understand how the mute function works, I am a newbie after all! Thanks for your help!

[kroto]

I think TDA7294 has a N.O. contact for the mute and standby function.
mean that when we turn it on (the mute function), the contact will close, so the signal will pass.
Simply connect the mute and standby pins to the +Vs will make the amp to work as common power amp.
Or, we connect it through resistor and capacitor to make a time delay function, this is useful to eliminate thump when the amp is powered on nor off.

You can see similar project (using TDA7293) at sound.westhost.com (maybe project127)
read how the muting function work.

Regards,

[Minion]

If you look in the TDA7293 Datasheet there is a PCB design that will work with the TDA7294 , I have used it a number of times with success , if you message me I can send it right to you if you want ......

Cheers

[Flashgun]

Originally Posted by kroto

I think TDA7294 has a N.O. contact for the mute and standby function.
mean that when we turn it on (the mute function), the contact will close, so the signal will pass.
Simply connect the mute and standby pins to the +Vs will make the amp to work as common power amp.
Or, we connect it through resistor and capacitor to make a time delay function, this is useful to eliminate thump when the amp is powered on nor off.

You can see similar project (using TDA7293) at sound.westhost.com (maybe project127)
read how the muting function work.

Regards,

So I should connect a +12V source to a pin and the ground to other pin of the mute function an see if that works out?

[kroto]

just connect pin #9 and #10 to pin #13, it will work as a common amp. no muting and standby.

[sesebe]

What is the voltage on output?
How much current draw?

In my tests at ±12V I have problems. Try with a bigger voltage supply.