TDA7294/7293 with reg input stage supply - diyAudio
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Old 13th January 2008, 02:54 PM   #1
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Location: 3RS
Default TDA7294/7293 with reg input stage supply

Has anyone measured the PSRR of the TDA7294 or 7293 with a regulated supply to the input stage. The PSRR in normal mode with common supply to input and output stage seems to be pretty poor.
I would expect such a regulated supply to be 'blue smoke' protected or BSP'ed , keeping in mind the reputation that these TDA's have for their affinity to emit BS or fireworks rather easily!

Is there any commercial application that reputedly keeps blowing , very easily ? Just curious.
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Old 15th March 2008, 07:37 AM   #2
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Hey ashok
The TD7293 is a nightmare. Your post caught my eye because I again could not take my own advice and have another Marshall MG100HDFX siting on my bench. Just as you described "smoke machine" I have seen so many of these that it is the typical problem with Marshall SS amps.
Just walk away.
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Old 15th March 2008, 07:55 AM   #3
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Hi rocinstruments ,
My TDA7294 is still working after many switch on/off cycles . In fact it sounds quite nice. I'm playing around with it to see how much it can be improved . I'm expecting blue smoke at some point but I have not yet reached that. I'll probably continue experimenting as I have some more spare 7294's. Then when they are all gone I'll call it quits !

Note that a breakdown will have a very scientific reason and if the work around is applied it will not breakdown anymore. You did read about the 'substrate' issue mentioned in an earlier thread. That seemed to be the cause of most deaths. Taking precautions about 'relative' voltages of the power supply pins should keep the chip alive.
The other possible reason , sometimes harder to solve, is if becomes unconditionally stable in an implementation and oscillates at RF and self destructs. There maybe it could be just a pcb design issue , apart from circuit issues.
There is scope for lots of experimentation.

PS. any chance of seeing the Marshall circuit and a picture of the pcb ?
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