OA trouble, 386 for 1/2v > 741's pin 3 @ 2.2Vdc

Started by petemoore, June 08, 2006, 04:20:12 PM

Previous topic - Next topic

petemoore

  ...Ramble, I'm typing in the hopes I'll see something I've missed, you can read and offer suggestions...
  The circuit is a Dist+, the supply via lm386 = 8.27v+, 4.12 as 1/2v, Gnd. is .0 V
  The other pins [not pin3 of 741] read:
  V+ is at 8.27v
  Output is at 4.10v
  -Input is at 3.90v
  +input is reading *2.2v
  The only thing really connected at all to pin 3 is a 1m which goes directly to, and reads ~1/2v supply at the 386 OA.
  So I'm getting a reasonable V/b, 4.12v from pin 5 of the lm386, and *2.2v on the +input of the lm741, with almost 1 meg resistance between them because
  DMM reads about 1 meg resistance between the +input and V/bias, pin 5 of the 386.
  I changed the opamp for an lm741.
  Pin3 ofthe 741, having only two connections at that node...it is easy to see that only the 1meg really attaches to anything, however I did check the 10k/input cap connections, it is all quite clean, I can't figure out why this circuit decided to stop functioning, it worked fine for a while or two.
Convention creates following, following creates convention.