op amp substractor resistance for practical

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ricoseeds

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I am using the 741 op amp circuit as a substractor..please tell me the value of the resistance I should choose.
with 1k resistance it didnt works...The circuit I used is attached...please reply asap..

**broken link removed**
 

All the resistors must be the same. They can be 1K or 10K, it does not matter as long as R1 = R2 = R3 = R4.

If the input voltages can be negative or positive, then you need a dual power supply. The circuit won't work with a single positive supply.
 

By 741 spec, 1k is already at the lower end of resistor range, at worst case it won't allow full +/-10V swing with +/-15V supply. 10k is pretty standard.

If I see a schematic diagram without supply voltages in a post like this "my OP does not work", I wonder, if supply is connected at all?
 
it was connected alright yet thanks a lot for replying ........
 

Hi rico,

when you really need help you should give us a bit more information than simply to say "with 1k resistance it didnt work".

Show us the complete circuit - including power supply and input signals - and describe your observations at the opamp output. Any signal? dc or ac?
 

What are the source resistances of your signal sources? They must be much lower than 1K (or whatever you are using as the resistor value) to avoid loading effects.
 

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