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.

 

[WHONOES]

If you are trying to make a 3 band tone control for your amp then why not use the commonly used Baxandall tone control. In its usual form it provide boost and cut for both bass and treble but is easy to modify to include boost and cut for the mid band. I use exactly that for my guitar amps.
It uses just 2 amplifiers both of which can be in the same package such as a TL072.
I can provide a schematic if required.

 

[danadak]

You might have G scaling in the 3 outputs and/or in the summer such that adding
a 3'rd input pushes the summer into clipping. Your BPF ringing ?

Schematic with values will help us to help you.


Regards, Dana.

 

[crutschow]

Seems unlikely that the TS has any further interest in this year old thread.

 

[Nikb]

Hi yes sorry. I do still have some interest in answers. Thank you for continuing to look. Unfortunately personal circumstances have forced me to do some other things in the last year. @WHONOES I'd be interested in the schema for the baxandall tone control. Thank you

 

[AnalogKid]

1. We're still waiting for your schematic so we can make some *informed* suggestions.

2. Search the word 'baxandall' and go to images for dozens of schematics.

ak

 

[crutschow]

Below is the LTspice sim of an example Baxandall bass and treble control circuit:

 

[davenn]

Thread closed, OP refuses to give required info even after multiple requests

@Nikb , you are just wasting everyone's time
IF you decide to finally give what is asked for, message me and I will reopen the thread

 

[bertus]

Hello,

You will find a lot of decent circuits on the following site:

ESP Projects Pages - DIY Audio and Electronics

ESP Project Pages - DIY audio projects. Amplifiers, preamps, crossovers, speakers, guitar amplifiers and lots more to choose from

sound-au.com

Bertus