lm4780 Zobal resistor burns immediately on Power ON

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megajocke

megajocke

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Joined 2003
This could have something to do with the grounding scheme in the amp - currents drawn by the amps or the zobel network may be causing positive feedback in some way.

The jumper on your layout (in purple) connecting power and signal ground should probably be removed or replaced with a 10 ohm or so resistor. Then the input circuitry connects via screened cable to the input jacks. Input jack grounds are wired together at the input jacks and then these are connected with a wire to ground at the power supply.
 
A

AndrewT

R.I.P.
Joined 2004
ashok said:
If a small length of cable at the input stops the oscillations it means you need to connect a capacitor at the input.
An average shielded cable has about 100pF per meter capacitance , so you can connect a 33pF or 47pF cap from input to ground. You could also add a series resistor of 1 k ohm from input to source. That would roll off the HF beyond 20 Khz.
Would you have any problems now ?
Click to expand...


kuldeepsingh said:



Thanx - This is the exact solution.... these were missing in my circuit..
Click to expand...
But, Fig5 has Cc=200pF.
Did you miss that out as well?
 
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