LM3886 in a powered speaker

[Bruce@bluff]

Greetings, I am repairing a powered speaker that has an tda7294 driving the compression driver and a TDA8954 on the low freq driver. They are fed from a common supply of app +-32v. The 7294 however has an offset of app 0.45v on the output which drops to few mv when an 8 ohm dummy load is connected when the dummy load is removed it goes back up to 0.45v again. I used a scope to check for oscillation. Is the chip faulty?

 

[Bone]

No

 

[Mark Tillotson]

Don't believe this is an issue - the output filter is ringing/clipping without a load, leading to artifacts like this, its not relevant to amp under load as the filter is then properly terminated.

 

[anti]

I too don't think that a TDA7294 in your "LM3886-powered speaker" is faulty.

 

[Bruce@bluff]

Thanks for the reply's yes I know LM3386 should be TDA7294. I put a sinewave in it today and see what comes out

 

[scottjoplin]

The offset is high