Re: uBITX - U1 Getting Fried - possible cause #ubitx

Jerry Gaffke
 

I think you're right.

The output pin has a quiescent DC voltage of around half the supply voltage, or about 6v,
so the 470uF cap will have a 6v charge on it when operating.  A significant bit of energy
for the TDA2822 to provide, and it tries to do so almost instantaneously in the case of a short.
A series resistor seems prudent. 

Perhaps the 470uF cap could be reduced to 100uF.
At 500hz the 100uF would have an impedance of 1/(2*pi*500*100e-6) = 3.18 ohms,
which seems borderline for good sound quality when using an 8 ohm speaker.

I vote for the resistor.  Something like 4 or 8 ohms, 1/2 Watt.
But worth experimenting if somebody has a stash of cheap TDA2822's on hand.

Configuring the TDA2822 for Dex's  bridge configuration does away with the cap charging problem,
but now the headphone jack has to be floating.  The bridge would be ideal for an internal speaker.

Jerry


On Thu, Mar 1, 2018 at 11:47 am, Jim Sheldon wrote:
My take is that huge 470 uF electrolytic in the output of the TDA2822M and the speaker gets a huge surge at turn on and during any loud noise or POP in the audio chain. 

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