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i built this circuit and its not working, help?

recently, i found a audio amplifier chip, the TDA7496 to be exact.
when i found its datasheet, it included a circuit for a audio amplifier.
i built that circuit, and it made my music quieter, not louder.
the sound level didnt change even when my input device was at max volume. (my laptop)
i tried the volume adjuster and it did work, but only to lower the volume, not raise it.

i followed the circuit, the 'mute' and 'standby' switches were hardwired to the 5v points, like the circuit shows the switches being at default (off)
the SGND seemed to be connected to PW_GND (tested via multimeter) internally, so i added a wire to ground externally to be careful.
im using a 15v power supply, and a 5v regulator.

i assumed all the down pointing white arrows were all to be connected.
capacitors 2, 3, 5, 6 and 8 were not put in.
i used polarized capacitors for 9 and 7.
all of the capacitors are rated for 16v.

i tried disconnecting the mute and standby lines, but that didnt change anything..
so ive attached the circuit in question, can someone tell me what might be wrong?
i have also attached the datasheet.

Picture of i built this circuit and its not working, help?
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C2,3,5,6 and 8 are VITAL for successful operation. You might even have damaged the amp using it without them.

You haven't followed the circuit, if you've omitted the parts that the circuit needs to work !!!

Steve
zack247 (author)  steveastrouk5 years ago
capacitors 2, 3, 6 and 8 are filtering capacitors, the circuit should be able to operate without them right? just maybe not clear sound?

i will find a capacitor for c5 and try again, hopefully i havent damaged the chip.
gmoon zack2475 years ago
2, 3, 6 and 8 are not "filtering caps."

They are "coupling caps."   Their primary function is to connect different stages within the amp by passing AC signals, while blocking DC. They do form various filters (high pass) with the other components, but they are not "filter caps."

A circuit might work work without 2 and 3 (if you are lucky). It almost certainly won't work without C6 and C8. That's the "power" end of the amp, and is capable of passing considerable current--consequently (as Steve says) passing the DC bias voltage here could seriously f-up your amp...
+1000. If there is a circuit, follow it, unless you really, really, really know what you are doing.
zack247 (author)  steveastrouk5 years ago
i added the caps and i guess i blew out the chip, i had sound for a little bit (mind you it was really fuzzy) and then it just stopped. giving me just fuzz.

it was a good thing i attached a heatsink, that chip got quite warm, the 7805 didnt, but the driver chip did.

im still happy that i got it to work at all, i guess this was a learning experience :P
i just used headphones to test it, and yeah, theyre no good anymore. luckily i have more.

if i come across another TDA7496 ill try this again, with all the capacitors.
it seems like it packs a fair punch, its too bad i messed it up :/
+++++ (the way to know what you are doing, i.e., to learn, is to follow the circuit ;-)

Best answer ---> Steve
The capacitors that you have not included do have to be there. They are actually coupling capacitors. They block DC (that will be present on the chip's pins) but allow a varying signal (audio) to pass. If DC is applied to a speaker it will drive its voice coil either in or out (depending on the polarity) and stay there (polarize). You will not hear much sound from a speaker in this state. Pins 12 & 14 will normally have about half the supply voltage on them which will happily polarize the speaker and start to burn out the voice coil. The chip itself could also be damaged.

Steveastrouk and Gmoon are quite correct, these capacitors must be there and you may have damaged the chip and the speakers.

Other potential issues; These high gain amplifier chips can be very cranky when it comes to their ground connections and physical placement of filter capacitors. Read the datasheet, it should give some helpful advice.
As Gmoon says the caps ARE NOT filter caps !!!

There is sadly a good chance you have either damaged the chip or the speaker.
Speakers don't like DC.

Steve
mh76dk zack2475 years ago
I agree in theory that leaving out the filtering caps should not be fatal, but on the other hand, before asking what is wrong it would not hurt to give the full circuit a try - just in case it really did matter :-)