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Op amp dirty signal.

P

peterken

Jan 1, 1970
0
Chris said:


It often helps to "decouple" outputs from their loads using small resistors,
especially if the loads have a capacitive component.
Often opamps begin oscillating caused by this component.
The small resistors used will cause a small voltage drop which will be
compensated by the opamp itself, so operation remains identical.

for IC1(A) (less needed here, but might help)
- small resistor (say 100e) from pin 1 to feedback junction
- small resistor (say 100e) from feedback junction to pin 2
(cut direct connection of course)
- small cap directly from pin1 to pin2
for IC1(D) (needed if load (out1) has a capacitive characteristic)
- small resistor (say 100e) from pin 14 to feedback junction
- small cap directly from pin14 to pin 13
for IC1(B) (needed if load (out2) has a capacitive characteristic)
- small resistor (say 100e) from pin 7 to feedback junction
- small resistor (say 100e) from feedback junction to pin 6
(cut direct connection of course)
- small cap directly from pin7 to pin6
for IC1(C) (needed if load (out3) has a capacitive characteristic)
- small resistor (say 100e) from pin 8 to feedback junction
- small resistor from feedback junction to pin 9 (cut direct connection of
course)
- small cap directly from pin 8 to pin 9

principle:
(see drawing in notepad using fixed font)

|\
-----|+\
| \-+-/\/\-+--
| / | |
+-|-/ === |
| |/ === |
| | |
|______+_/\/\-+
 
C

Chris

Jan 1, 1970
0
Input looked the same ,. well turns out it's an bad wall socket,
realised this when i checked my probe on the scope and got a little jolt
moved it all off to another socket and a nice signlan added a small cap
filttered it right down :)
 
peterken said:
It often helps to "decouple" outputs from their loads using small resistors,
especially if the loads have a capacitive component.
Often opamps begin oscillating caused by this component.
The small resistors used will cause a small voltage drop which will be
compensated by the opamp itself, so operation remains identical.

for IC1(A) (less needed here, but might help)
- small resistor (say 100e) from pin 1 to feedback junction
- small resistor (say 100e) from feedback junction to pin 2
(cut direct connection of course)
- small cap directly from pin1 to pin2
for IC1(D) (needed if load (out1) has a capacitive characteristic)
- small resistor (say 100e) from pin 14 to feedback junction
- small cap directly from pin14 to pin 13
for IC1(B) (needed if load (out2) has a capacitive characteristic)
- small resistor (say 100e) from pin 7 to feedback junction
- small resistor (say 100e) from feedback junction to pin 6
(cut direct connection of course)
- small cap directly from pin7 to pin6
for IC1(C) (needed if load (out3) has a capacitive characteristic)
- small resistor (say 100e) from pin 8 to feedback junction
- small resistor from feedback junction to pin 9 (cut direct connection of
course)
- small cap directly from pin 8 to pin 9

principle:
(see drawing in notepad using fixed font)

|\
-----|+\
| \-+-/\/\-+--
| / | |
+-|-/ === |
| |/ === |
| | |
|______+_/\/\-+

Gee, your schematic looks just fine with the fixed font in this entry
window. Don't ya just love how people 'fix' things?
GG
 
C

Chris

Jan 1, 1970
0
small cap, ceramic? about how small?


Thanks
 
P

peterken

Jan 1, 1970
0
Chris said:
small cap, ceramic? about how small?


Thanks

depends on the highest frequency you want passing through the circuit of
course since it's a filtering circuit
I'd begin with say 1nF and go up by decade while looking at the signal on
your scope until the output satisfies your needs
 
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