My first Lm3875 experience

[AndrewT]

connect the extra winding out of phase with one of the original windings.
Measure the voltage across the two open ends. That Vac is your "error".
Yes, it may be a few turns short. These can be added to correct the extra winding.

 

[atupi]

Very good idea to connect winding out of phase and measure.

 

[atupi]

Last evening tried to listen again to my old gainclone made by following the National app note. The problem is that i have the positive rail on the SPK output and i dont understand why.

The voltages are the following on LM pins:
7: 1V
8: 28V
1: 29V
4: -29V
3: 28V (output)

Any clue ?

 

[AndrewT]

No DC block on Input.
No RF attenuation on Input.
No Output Zobel, nor Output Thiele Network

Does your Cs incorporate both HF decoupling and MF decoupling?

 

[atupi]

But how input cap or RF attenuation or Zobel would help me not not have that DC on output ?

 

[AndrewT]

Oscillation may have killed your chipamp !!!!!!

 

[godfrey]

Or two wires are touching in the P-P wiring.