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This is the circuit I will be referring in this question:

enter image description here

TDA7294 is described in this data sheet. Upper IC with added external components is a well-known circuit and can be found on many websites and shops, so I presume someone will be reading this with experiences of building an audio amplifier with this IC.

I have build the upper circuit on PCB and tested it. First thing it happens, when I connect power supply leads to +Vs/0/-Vs is that huge amount of current (just like a short-circuit) starts to flow through -Vs (negative rail). +Vs (positive rail) was supplying about 0.5A, while -Vs was supplying more than few amps, while both output connections and input connections were disconnected to speaker/input source. I replaced several TDAs, where all of them show same results. I verified every connection of the circuit between external components and TDA three times, where all connections on PCB were right were they should be. I even breadboarded this circuit two times, where the results are the same as for the circuit built on PCB.

I connected VM (Mute) and VSTBY (Stand-By) to positive rail, as it should be for normal operation of amplifier, where the result were the same as explained before. I also disconnected MUTE (pin 9) and STBY (pin 10) out of circuit, where the results were the same.

But I noticed that if I disconnect IN+MUTE (pin 4), that all the sudden, current consumption of circuit is almost zero. But the circuit still doesn't work with IN+MUTE pin disconnected. Even if it is connected to ground, the circuit doesn't work. It doesn't work in means of applying source signal to input of TDA and scoping output signal without load. In both cases, scope shows nothing at all - straight line.

Would it help in this case, if I would connect "Boucherot cell" to output of the TDA amplifier? Or can I do anything about it at all? Sincerely, I have no idea what else to do about this circuit...

NOTE: I would have made a LTSpice schematic and tried it there too, but Spice's library doesn't include TDA7294, or any TDA at all.

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  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$
    – Dave Tweed
    Jul 17, 2018 at 20:02

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I would suggest ordering a TDA7294 from a reputable supplier like RS Components or Farnellinone and replacing the device in your board. There are a very large number of counterfeit parts coming out of the Far East so although the board and passive components may be OK I would suspect the TDA if it were me. If you remove the device from the board and measure with a multimeter set to read resistance particularly the ground pin to 7,8,13,14,15 any sign of low resistance will suggest an internal short circuit. Also measure most combinations of these pins in the same way.

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  • \$\begingroup\$ This project of mine is rather old and I abandoned it already, but thank you for telling me what you think. Judging by my experiences upon using different TDAs I would say that TDAs can be generally seen obsolete and many problems can occur when building a project like this due to its age. If I would go for another such amplifier project, I would choose power integrated circuit, whose year of production is a bit less older that in case of TDAs. \$\endgroup\$
    – lucenzo97
    Jan 13, 2020 at 16:04
  • \$\begingroup\$ Hi Keno I have built a very successful amplifier with the TDA7294 consisting of 4 devices 2 of each in bridge mode for 2 channels(stereo). I found that every device needs the full compliment of de-coupling capacitors on all supply pins as in manufacturers data to guarantee stability. Initially all TDA's ran hot due to oscillation the decoupling cured it completely and produced a very acceptable amplifier, the board I used from China had to be adapted by soldering the capacitors on the back but it was worth it The TDA 729X are fully current in production and available from RS and Farnell \$\endgroup\$
    – Chris
    Oct 1, 2020 at 7:13

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