Help with merging guitar stereo outputs please

[Potato Cakes]

Oh I see what you mean. So one resistor would be placed between the union of the red cables and the output jack tip, and the other between the union of the blue cables and the other output jack tip? Is that correct?

Thanks !!
Sono

Two resistors per cable color. Where they connect is goes to the amp. Do a quick search for summing network or summing bus resistors and it should make sense.

Thanks!

Paul

 

[sonolink]

Hi again guys,

I'm back at this little project again. After speaking to my friend, he needs the FX tails to be kept so I've drawn a little schem with all your suggestions:


What do you guys reckon?
Thanks a lot for your time and help

Cheers
Sono

 

[Chandra]

Boss Line select LS2 does exactly what you need, but in mono.
A or B, in many combinations, and has output control for both A and B loops.
You can look at the schematic and duplicate for stereo and may simplify it to suit.
Regards.

 

[sonolink]

Thanks for chiming in Chandra. Anything wrong with my diagram? Thanks for your suggestion but I can't seem to find a schem for the LS-2 anyway. It's a shame it doesn't have stereo outs...

Cheers
Sono

 

[Hubbub]

Your diagram in #22 should work fine provided the four output summing resistors are all the same rated value. That value needs to be maybe 5x-10x the output impedance of each device and probably no more than 20%-30% of the input impedance of the amp it will be feeding. Would be good to use 1% resistors, or 5% parts that read within 1% of each other.

 

[Chandra]

I would suggest both loops have the input signals all the time.
You switch only the outputs of these loops.
Use electronic switching for low current consumption from battery or use a relay if power from adopter.
There is another model AB2 from Boss which might be useful for you to adopt, still mono.
Regards.

 

[sonolink]

Your diagram in #22 should work fine provided the four output summing resistors are all the same rated value. That value needs to be maybe 5x-10x the output impedance of each device and probably no more than 20%-30% of the input impedance of the amp it will be feeding. Would be good to use 1% resistors, or 5% parts that read within 1% of each other.

Thanks Hubbub,
Those resistors are all the same indeed. Probably 5k/1%

I would suggest both loops have the input signals all the time.
You switch only the outputs of these loops.
Use electronic switching for low current consumption from battery or use a relay if power from adopter.
There is another model AB2 from Boss which might be useful for you to adopt, still mono.
Regards.

Chandra, my guess is switching should be done before each FX chain to avoid cutting off reverb tails.
Thanks for your input and suggestions anyway

Cheers
Sono

 

[Chandra]

Thanks Hubbub,
Those resistors are all the same indeed. Probably 5k/1%



Chandra, my guess is switching should be done before each FX chain to avoid cutting off reverb tails.
Thanks for your input and suggestions anyway

Cheers
Sono

If you want the reverb tail to continue, you will also hear the not so silent distortion and crusher or if there is any modulation going upfront. Anyway, it is up to you.
Regards.

 

[Whoops]

I can't seem to find a schem for the LS-2 anyway. It's a shame it doesn't have stereo outs...

The GGG circuit you show for the switching also doesn't have Stereo Outputs...

not different than the LS-2 in that regard

 

[sonolink]

If you want the reverb tail to continue, you will also hear the not so silent distortion and crusher or if there is any modulation going upfront. Anyway, it is up to you.
Regards.

You're right. But it's not up to me, but my friend that wants those Fx chains

The GGG circuit you show for the switching also doesn't have Stereo Outputs...

not different than the LS-2 in that regard

I'm afraid I differ. The LS-2 has 2 loops that allows you to commute an input between them but also have a return that merges into a mono out. The GGG circuit is just a switcher between 2 different mono outs. That's why I need a summing network at the end of both FX chains if I want to go that route.

Chandra's suggestion is actually cool except that my friend REALLY wants to keep the stereo outputs at the end of each FX chain. And that, as I pointed out, is up to him, really

Thanks again to everyone for their input, help and ideas. I heartedly appreciate it.
Now I have to see if I can fit everything in the dimensions he has asked me to which is a altogether different war

Cheers
Sono

 

[Whoops]

The GGG circuit is just a switcher between 2 different mono outs.

The GGG circuit is a simple AB box, the LS-2 has different modes can be many things, it can also just be a simple AB box like the GGG circuit.
That was what I was referring to.

Good luck and good work

 

[sonolink]

Hi again guys!! I built the little box according to the last pic and everything sounds and works fine! Thanks again to everybody for your time and help. My friend has asked me for a little mod: the possibility to add a minijack input to insert some playback while playing. He would also like a pot to level the playback with his guitar playing. So I added a female mini-jack and connected it to a dual 100k pot since it's a stereo signal (pin 1 to ground, pin 2 to output and pin 3 to input), and connected the output pins of the pot to the output jacks like so:


The problem is that when I move the pot the volume from the guitar is affected aswell, not only the playback. Is that because I didn't put summing resistors to the playback output like so?


If that wouldn't be the reason, any ideas?

Thanks a lot
Cheers
Sono

 

[Hubbub]

Not only do you need the summing resistors, but you need them fed from a constant impedance source. Your volume control isn't constant impedance, so it needs to be buffered by an amplifier of some sort to isolate the added volume control from the mixing circuit. A simple op-amp voltage follower (gain of +1) would be adequate to do that part of the task. An op-amp inverter (gain of -1) might prove better sounding than a voltage follower as it avoids some op-amp input stage distortion effects.

 

[sonolink]

Thanks for your quick reply

Something like this would do? Chip would be TL072. Bias would be 9v?
Thanks!

 

[Hubbub]

Nope. The volume control needs to be before the amplifier, just the cap and summing resistor after. For lower distortion the input bias voltage needs to be about .3 to .4 times the op-amp supply voltage, and bypassed with adequate capacitance to keep the channels from talking to each other. Note that this significantly limits the maximum signal that can be handled, but using .5 times the supply adds lots of distortion to low-level inputs. (i.e. get a better amp!) Fortunately for the FET input TL072 the bias resistors do not need to be the same value as the feedback resistor, and can be much higher so as to not so significantly load the volume control. Because the bias resistor will load the volume control you may want a modest amount of gain in the op-amp stage. Having the feedback resistor at 1K loads the TL072 output significantly, so bumping that up a bit for gain helps make more drive available for the summing stage.

 

[sonolink]

Like this?

For lower distortion the input bias voltage needs to be about .3 to .4 times the op-amp supply voltage, and bypassed with adequate capacitance to keep the channels from talking to each other. Note that this significantly limits the maximum signal that can be handled, but using .5 times the supply adds lots of distortion to low-level inputs. (i.e. get a better amp!) Fortunately for the FET input TL072 the bias resistors do not need to be the same value as the feedback resistor, and can be much higher so as to not so significantly load the volume control. Because the bias resistor will load the volume control you may want a modest amount of gain in the op-amp stage. Having the feedback resistor at 1K loads the TL072 output significantly, so bumping that up a bit for gain helps make more drive available for the summing stage.

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:



"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:



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

 

[Hubbub]

The above pic (#36) is correct for the circuit. For a TL07x with 9V supply consider 3-3.5V bias to avoid the input crossover distortion that happens at 1/2 supply. Yes, bump the feedback resistor R6 to 2-3K. C3 can be much smaller (18nF) since it is now working with the 1M bias resistor to set the LF corner. (Leave it the same and the turn-on time will be multiple seconds, not nice.) I would also consider using an OPA1688 instead of the TL07x, but I have not tried it.

 

[sonolink]

Would this PSU be ok? I think I'd get 3.6V




Thanks a lot!
Cheers
Sono

 

[Hubbub]

Close. Add a 10uF capacitor from bias to ground. Give that a try.

 

[sonolink]

You mean parallel to the 10k and 100k resistors?

Cheers
Sono