Mixing output from 3 op amps

[Nikb]

Hello. I've used 3 op amps to make bass, mid and treble controls for a guitar audio signal. I basically split the signal out through the 3 separate controls and then remix it using another op amp with no gain. I have used an op amp as a buffer at the input. When I mix 2 of the control outputs they work great but adding a 3rd op amp seems to effect the output of the other 2 in odd ways. Can the output of several op amps be mixed using another op amp or is this a no no? Could this be the simulation software? Sorry for the basic question. I'm trying to work out if I've made a basic error in the design or an error of principle. Thank you.

 

[kellys_eye]

Schematic?

 

[Harald Kapp]

Schematic?

+1

Look up summing amplifier.

 

[Nikb]

Yes - sorry - I've so many variations of this circuit I'm trying to decide which is the best to post. Essentially I'm testing this in circuitlab. I'm splitting a single single input into 3 lines through second order high pass, low pass and band pass filters using op amps. I'm then remixing the output from the 3 op amps using a summing op amp. This works if I connect any 2 of the filters but 3 filters only works if I sum 2 with an op and then sum the output of those with the 3rd with another opamp. I was asking really is this a limitation of circuit lab or a behaviour of the op amps? i.e. using a summing op amp to sum the output of 3 opamps won't work? I think I'll have to build the circuit IRL to test this?

 

[danadak]

Post your simulation

 

[Harald Kapp]

I was asking really is this a limitation of circuit lab or a behaviour of the op amps?

Neither. It's your circuit which you still haven't shown.