Lm391 N100

sakis · 27th April 2009, 04:15 PM

everybody has been arround this ic some times

havent touch any of them for years but out of the blue one amp that used it come in to the shop for repair .

while searching first for the ic it shelf ( it was blown beyond repair he he

) then i looked at the application which was the exact copy of the original application as given by national .....

then i noticed that eventhough i bias network exists to provide adjustable bias for the drivers and output there is no vbe multiplier ,,,,,,meaning that as amplifier warm probably bias will drift ....upwise as usual

any ideas ???? am i missing something ???

lms · 27th April 2009, 04:20 PM

vbe multiplier is in the LM391, which should be thermally coupled to the drivers for best bias stability

sakis · 27th April 2009, 04:36 PM

but is something like that writen in the manual ????

if it is i missed it

mjf · 27th April 2009, 05:40 PM

hello.
i looked at the datasheet of a lm 391 (www.datasheetcatalog.com).
vbe - biasing is built in...........and some other examples for user are shown.
greetings................

wg_ski · 27th April 2009, 05:40 PM

No , the data sheet didn't mention keeping the chip thermally coupled to the drivers. It just suggested a minimum value for Re which insured thermal loop stability (which does not necessarily mean zero drift).

27th April 2009, 04:15 PM	#1
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	Lm391 N100 everybody has been arround this ic some times havent touch any of them for years but out of the blue one amp that used it come in to the shop for repair . while searching first for the ic it shelf ( it was blown beyond repair he he ) then i looked at the application which was the exact copy of the original application as given by national ..... then i noticed that eventhough i bias network exists to provide adjustable bias for the drivers and output there is no vbe multiplier ,,,,,,meaning that as amplifier warm probably bias will drift ....upwise as usual any ideas ???? am i missing something ??? __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

27th April 2009, 04:36 PM	#3
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	thanks for your suggestion but is something like that writen in the manual ???? if it is i missed it __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

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27th April 2009, 04:20 PM	#2
lms diyAudio Member Join Date: Aug 2004 Location: beach	vbe multiplier is in the LM391, which should be thermally coupled to the drivers for best bias stability

27th April 2009, 05:40 PM	#4
mjf diyAudio Member Join Date: Jan 2009 Location: upper austria/near linz	hello. i looked at the datasheet of a lm 391 (www.datasheetcatalog.com). vbe - biasing is built in...........and some other examples for user are shown. greetings................

27th April 2009, 05:40 PM	#5
wg_ski diyAudio Member Join Date: Oct 2007	No , the data sheet didn't mention keeping the chip thermally coupled to the drivers. It just suggested a minimum value for Re which insured thermal loop stability (which does not necessarily mean zero drift).

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