Combining output from phone with output from amp

[Locrian99]

Hello,

I have a small pedalboard amp that has an 8-16 ohm output.   I've made a little box with ts to trs jack and use it with 32 ohm headphones completely passive seems to work.   I want to add an aux input in my box.   Which I did by simply adding another jack and connecting the trs to the appropriate spots on the headphone out.    Still completely passive.   Works fine from my aux (iPhone with lighting to 3.5mm adapter if it matters).   Moment I plug the amp in as well significant volume loss from the aux source.   I can turn my phone up to compensate but at max volume it's not as loud as I'd like it to be able to get and I get clipping. 

I was hoping to keep this passive and just use the phone volume and amp volume (ehx howitzer if it matters).   I'm thinking that's not going to work at this point and j likely need to add a mixer circuit something like this? 

https://tagboardeffects.blogspot.com/2013/01/2-channel-mixer.html?m=1

Is a simple buffer the right answer, or? 

End goal to be able to play through headphones with backing track or drum machine track.  Not sure if there would be an impedance difference between that and a phone. 

Thanks.

[antonis]

Is a simple buffer the right answer, or?

Or a simple mixer..

In case of Ch1 - Ch2 considerable impedance mismatch, you can alter respective 100k resistor value..
(lower its value for respective Channel lower output..)

[deadastronaut]

ive been down this path too recently.

tried to make it all passive, no chance.....

ended up having to make a small mixer for the inputs as antonis suggests....


with mine i made it so that the phone can record video/audio and cut off the internal phone mic, so no external noise etc..and playback too, using a TRRS cable... (note android and apple swap the R'2 AND S over....the muthas. 

which is great for recording direct demos etc...or just fun.

[marcelomd]

This is part of the preamp of a clean power amp I've built. Input buffer + master volume and aux input from phone/computer. Simple and effective. No noise issues.




EDIT: Just noticed the volume potentiometer is wired backwards in this schematic.

[Locrian99]

Thank you, I'll toss that mixer together on strip board and see how it works out.   

[garcho]

Is the aux input made for standard stereo? Normal TRS stereo is T = left, R = right, sleeve = ground. The schematic has ring and sleeve mixed up.

[marcelomd]

Is the aux input made for standard stereo? Normal TRS stereo is T = left, R = right, sleeve = ground. The schematic has ring and sleeve mixed up.

Mine? I put ground in the middle for layout reasons only. The jack I used is panel mounted, so I just connected the wires to the correct places.

[Locrian99]

Hmm.   Interesting.   

So threw the mixer together following layout linked in the original post.   Somewhat regret not breadboarding it first as it would make playing with values easier.   Aux input sounds great.    Guitar sounds muffled with op amp clipping I'm assuming I just need to play with the value of that resistor coming from leg two of the pot before the op amp.   Should I raise or lower ?   And do I need to go big to make a difference like instead of 100k go to 1 Meg?  Or ?  Would rather not solder and resolder this strip board 30x

[antonis]

Raise..

[Locrian99]

Ok so I've been kind of messing around with this a bit, it's working alright.    But I haven't been super thrilled with it.    I have a few power amp module boards I laying around I was going to try to toss something together, so I was looking at some of the schematics over at electrosmash for ideas on that.   

They have the aux inputs on the two examples I looked at basically right before the power amp, and it's 100% passive.   There doesn't appear to be any blending etc.   makes me wonder if I could put this box in the effects loop of the amp I'm currently using and have it be a passive box. 

https://www.electrosmash.com/images/tech/1wamp/1wamp-schematic.png

https://www.electrosmash.com/images/tech/mg10/marshall-mg10-schematic-parts-big.jpg

Looks like really it's just a couple resistors and a jack to add.  Could I just add a box like that on the effects loops (obviously it would be the last thing for it to hit, and keep it passive?  Just have both the guitar signal, and aux signal meet as in the schematic?).   Should I have to worry about adding anything else to the guitar signal side or the output after they meet before they hit the fx loop return combined. 

Thx.

[marcelomd]

Note that the aux inputs are being mixed passively with the series resistors but actively with the guitar signal (via the inverting input of the next stage).

[Locrian99]

Which is what I'm wondering is would the power amp portion that the signal would hit after the fx loop essentially do the same thing?   I can easily enough just try it, when I get an around my bench again tonight.   But just curious if I'm thinking on the right track here. 

[Locrian99]

Actually it works awesome!   There was a big disparity between the resistors used between the two examples I had I ended up just using 9k1 from the tip and ring of the aux in, the efx loop send jack and those two all go to the tip of the out which I just connected to the effects loop return.   Sounds awesome, I'll just have to make a little box for a headphone out from the amp output and I think everything can be passive.