Help with merging guitar stereo outputs please

[Hubbub]

Yes

 

[sonolink]

Excellent. Thanks A LOT for your help. I'll build right away although I don't know how I'll fit everything in the enclosure. Thanks again!!
Cheers
Sono

 

[sonolink]

One last check please

 

[RoadrunnerOZ]

Like this?

View attachment 114900


I'm not sure I follow you completely. Please excuse my language barrier

If the above pic is correct (vol pot before), should I now find a way to feed 4.5v for Bias to the TL072? And should I use more resistance on the feedback resistors? (like 2-3K)

Just out of curiosity: is it not possible to have a similar circuit with a pot but passive?
I'm asking because when I first added the Audio In to the box I kinda copied a modified guitar wiring like this one:

View attachment 114905

"Neck" and "Bridge" are the pickups (sound source) and this circuit doesn't need summing resistors or active parts when the switch sums both pickups in the middle position.
With this in mind I modded it like so:

View attachment 114906

In the guitar circuit, adjusting one pot doesn't seem to affect the other. So why does it affect the Timeline and AmbiSpace return levels in my box and not only the stereomplayback IN? I'd really like to understand it

Thanks for your time and help
Sono

The above diagram for the original wiring works because in the switch centre position (both pickups) the vol pots for both would be turned up - turn one down, they both go down. In the single positions, either neck or bridge, the other pot is out of circuit. What you extracted won’t work as you will shunt the signal of both to ground when you turn either pot down.
The problem with passive summing is the gain loss - I’d be maybe looking at summing both A and B stereo outputs with trim controls for setting fixed levels using a TL074 and then a TL072 with a volume control or trimmer for the injected stereo signal (or a TL074 using the two extra opamp channels for final stereo summing of all -
A, B and inject - and having a master gain pot or trimmer on that stage.
You could also incorporate a switch to make the output mono by switching right channel connection from the ring to the tip of the output jack - (or switching the inputs of all the right channel IC’s to the left channel IC’s so you get a summed mono output on the tip of the output jack but this involves more work).
Most synths have a left/mono output jack, both channel outputs wired to the left socket - when you plug into the right output socket the switch in that jack socket transfers the right channel signal to itself and lifts it from the left socket - dead simple to replicate with a SPDT switch on a TRS socket if that’s what you’re using for stereo signal output.

 

[Hubbub]

One last check please View attachment 114919

Looks good!

 

[Hubbub]

As for help understanding why the added volume control in #32 affects the mix you need to realize that the circuit is a summer where the result depends on the source impedances and combined resistances of the mix circuit. The modules that do signal processing have a low output (source) impedance that does not change. Add in a pot on the 3rd input and its source impedance varies with pot position, as does the effective resistance for the mix.

Theoretically you can study superposition, which is well explained here: https://www.allaboutcircuits.com/textbook/direct-current/chpt-10/superposition-theorem/

In applying superposition the resistances are (must be) constant, but when you add your pot into the circuit now you have a varying resistance, and the network solution changes with each different pot position. Different solution means different volume for the mix.

 

[RoadrunnerOZ]

As for help understanding why the added volume control in #32 affects the mix you need to realize that the circuit is a summer where the result depends on the source impedances and combined resistances of the mix circuit. The modules that do signal processing have a low output (source) impedance that does not change. Add in a pot on the 3rd input and its source impedance varies with pot position, as does the effective resistance for the mix.

Theoretically you can study superposition, which is well explained here: https://www.allaboutcircuits.com/textbook/direct-current/chpt-10/superposition-theorem/

In applying superposition the resistances are (must be) constant, but when you add your pot into the circuit now you have a varying resistance, and the network solution changes with each different pot position. Different solution means different volume for the mix.

In some passive mixing circuits the take-off is from the top of the pot, with the input from signal source going to the wiper via feed resistors and the output via summing resistors from the pot top to mix bus. This also can occur in Aux outputs from a mixer channel to the Aux bus lines - for example a 5K1 resistor feeding the wiper of a 50K pot, top of pot is output to the Aux bus like in the Mackie SR-24, the position of aux 1 pot on any channel doesn’t affect others strapped to that aux 1 bus.
I assume this reduces somewhat the unwanted gain changes from each pot interacting with adjacent summing circuits when a wiper goes to ground if that’s your output source.

 

[Chandra]

Connecting input to +ve input of opamp will not be the best.
Connect to the -ve input though a resistor say 250 k (R11).
Additional inputs may be connected to the -ve input using another resistor.
Keep R10 1-3 times of R11
The +ve input can be directly connected to R1 R2 junction without R9
Regards.