Resistor from Pin + (7) to ground in inverted GC
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 31st August 2006, 08:57 AM #1 100db   diyAudio Member   Join Date: Dec 2005 Location: Bangkok, Thailand Resistor from Pin + (7) to ground in inverted GC Hello all, For the inverted LM-3875, I need your advice on the different between having ... 1. Resistor between Pin + (Pin7) to ground 2. Resistor in parallel with 0.1uF cap to ground and... 3. Connect pin + directly to ground ? How is it work, and which one should give the best sounding ? Thanks Ball
 31st August 2006, 09:31 AM #2 pinkmouse   diyAudio Moderator     Join Date: Apr 2002 Location: Rotherham, England I would go for a direct connection, but it's simple enough to test all three and see which you prefer. __________________ Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
 31st August 2006, 11:12 AM #3 jan.didden   diyAudio Member     Join Date: May 2002 Location: The great city of Turnhout, BE Its a nice story, really: Part of the amp DC output offset is caused by the difference in DC bias at the two inputs. Those two inputs need a small DC bias current to work (base current of input transistors). So if the DC impedance seen by those bias currents at the two inputs is different, the DC voltage resulting from current times impedance is also different and will cause output offset DC (the input DC difference will be amplified by the amp closed loop gain of course). So, very often you see the pin 7 resistor as being equal to the DC resistance of the - input to balance out the offset. The DC resistance seen at the - input is the parallel value of the two resistors in the feedback network (if it is DC coupled, else it is just the value of the main feedback resistor). Jan Didden __________________ Cable: a potential source of trouble interconnecting two other potential sources of trouble - Erik Margan Linear Audio pubs and articles . The SilentSwitcher now at diyaudio store SilentSwitcher. Keeping in touch with SY.
 1st September 2006, 12:28 PM #4 100db   diyAudio Member   Join Date: Dec 2005 Location: Bangkok, Thailand Thanks Al, Thanks Jan So, if I don't have any problem with DC offset... then it's O.K. (better) to connect pin + directly to ground. Am I understand this correctly ? Will try it out this weekend. Ball

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