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Old 11th April 2012, 09:33 AM   #21
AndrewT is offline AndrewT  Scotland
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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.
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Old 11th April 2012, 10:35 AM   #22
atupi is offline atupi  Romania
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Very good idea to connect winding out of phase and measure.
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Old 7th March 2013, 07:54 PM   #23
atupi is offline atupi  Romania
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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 ?
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File Type: jpg LM3875-FIG-1-SPLIT-SUPPLIES.JPG (3.7 KB, 118 views)
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Old 8th March 2013, 08:43 AM   #24
AndrewT is offline AndrewT  Scotland
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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?
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Last edited by AndrewT; 8th March 2013 at 08:56 AM.
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Old 8th March 2013, 10:57 AM   #25
atupi is offline atupi  Romania
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But how input cap or RF attenuation or Zobel would help me not not have that DC on output ?
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Old 8th March 2013, 10:58 AM   #26
AndrewT is offline AndrewT  Scotland
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Oscillation may have killed your chipamp !!!!!!
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Old 8th March 2013, 11:29 AM   #27
godfrey is online now godfrey  South Africa
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Or two wires are touching in the P-P wiring.
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