op amp substractor resistance for practical

[ricoseeds]

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**

 

[godfreyl]

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.

 

[FvM]

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?

 

[ricoseeds]

it was connected alright yet thanks a lot for replying ........

 

[LvW]

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?

 

[Kral]

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.