A question of op-amps!

[Guest Grenouille3]

I'm building an amplifying circuit on PCB using two 741 op-amps, both inverting, giving an overall gain of 10. My output signal though has spikes...I've tried decoupling the power supply and that doesn't make any improvement, is there anyway to get rid of the spike and get a steady output from the op-amp circuit?

[YT2095]

have you tried local de-coupling capacitors across the power to each?

 

0.1mfd (marked as 104 on ceramic caps) as close to the IC as possible should do the trick, although you don`t state the application or the frequency range used?

 

this will work for MOST applications

 

edit: and why use 2 of them if you only want a gain of 10?

[Douglas]

I'm building an amplifying circuit on PCB using two 741 op-amps, both inverting, giving an overall gain of 10. My output signal though has spikes...I've tried decoupling the power supply and that doesn't make any improvement, is there anyway to get rid of the spike and get a steady output from the op-amp circuit?

What are you using for a power supply? It's sounds like a chopper. Are you decoupling right on the 741 supply pin(s) with a .01 mf capacitor and with the capacitor leads no longer than 1/4 inch? Do you have plenty of ground plane on the PCB? Keep your leads short from supply to PCB and bypass your supply with a 10 mf cap right at the terminals.

[RICHARDBATTY]

Have you used any feed back?

[Guest Grenouille3]

At the moment, i'm decoupling at the power supplies. it's +/- 15 Volts into the 741. Do you think feedback is a feasible option? Would it make the op-amp characteristics more ideal and stabilise the output?

[RICHARDBATTY]

feed back - helps to center these sorts of circuits.

[Douglas]

At the moment, i'm decoupling at the power supplies. it's +/- 15 Volts into the 741. Do you think feedback is a feasible option? Would it make the op-amp characteristics more ideal and stabilise the output?

Are you talking about op amp feedback? If so, you can't operate an op amp ( at least the 741) without feedback. Why do you need 2 op amps for a gain of 10?

[YT2095]

you still don`t state what sort of frequency range they`re to used at?

 

have you considered using a RC twin `T` low pass filter, either on the input stage or the output?

 

you could use an RC or LC filter across your power rail too, op amps don`t use that much power so filtering the rail won`t be an issue. (it`s good practice to do this for all amp circuits anyway).

 

do you know anyone with a dual trace scope you could use, you`de find the problem in seconds that way!