Seeking two player silent band rehearsal device advice

[Krystal]

The title is probably unclear, sorry, language is hard sometimes.
The question is this :
Two of us (bass & guitar) playing in a flat, we have two amps with headphone outs, no line outs, how do i mix both headphone outs to two pairs of headphones ?
I first thought :

input 1---buffer---\                      /ouput1
                    summing amp---splitter
input 2---buffer---/                      \ouput2

But the amp's headphone outs won't be too pleased to see a buffer instead of headphones right ? Is this were DI boxes come in ?

Is this just not the way ?

I've looked some of this stuff up of course but just came away more confused.

Also if there's a simple and cheap solution to this that i can buy that's fine too.

Thanks !

[antonis]

But the amp's headphone outs won't be too pleased to see a buffer instead of headphones right ?

Why..??

[Krystal]

Well as i said, i'm pretty confused at this point, but doesn't the headphone out require to be connected to a low input impedance ? Won't it be super quiet ?
I don't know, that's why i'm asking.

[FiveseveN]

No, not at all. The headphone amp has low source impedance, which allows it to drive lower impedance loads. It will be more than happy with higher-Z loads.
It also means there's no need for buffers before the summing amp.
Do you want the mix in both headphones to be the same?

[Krystal]

OK, cool !
I would probably have a volume pot for each input and each output, but same mix for both outs, we want to hear the same thing (or close enough).
Thanks!

[FiveseveN]

I'm betting the amps have volume controls so that can take care of setting the absolute amplitude and relative balance of the two (or four if they're stereo) signals.
You can use a simple resistor mixer or any of these options: https://sound-au.com/articles/audio-mixing.htm depending on what kind of headphone amp you go for (and its input Z).

[jorg777]

If both amps have plenty of extra loudness on the headphone outputs, you might get away with as little as two fixed resistors to do the whole job.  Something like 16 to 32 Ohms.

[Krystal]

I was thinking of doing the basic inverting summing amp (fig4 in your link). I'd use the second half of the dual op amp to split the signal and then buffer the outs if necessary.

depending on what kind of headphone amp you go for (and its input Z).

Do you reckon I'll need a headphone amp after the mixer? Isn't the previous amp already doing the amplifying? I mean the actual guitar amps, not the summing.

I'm betting the amps have volume controls so that can take care of setting the absolute amplitude and relative balance of the two (or four if they're stereo) signals.

Yeah, the extra volume pots would just make life easier, no bending down under the desk tweaking the amps' touchy knobs. Also, no stereo, keeping things simple for the moment. The idea is just to be able to bang away at guitars together without being a nuisance to neighbours.

EDIT:

If both amps have plenty of extra loudness on the headphone outputs, you might get away with as little as two fixed resistors to do the whole job.  Something like 16 to 32 Ohms.

Plenty loud. The guitar amp I wouldn't push past 9 o clock with headphones on. A Peavey Rage 158, no laughing matter.

[FiveseveN]

Do you reckon I'll need a headphone amp after the mixer? Isn't the previous amp already doing the amplifying?

But you're not connecting the headphones to the previous amp, you're connecting them to the mixer. And most op amps struggle to drive heavy loads, with exceptions like NJM4556.

[quad4]

Also if there's a simple and cheap solution to this that i can buy that's fine too.

I've used the Rolls MX28 Stereo MINI-MIX VI. It's cheap, solid, and decent. Not going to win any cork sniffing competitions, but it works.

It also converts mono inputs to stereo (dual mono?). You can pan any input.

There are two headphone outs tied to the same volume control.  You can also drive headphones on the master output (add a dual mono to stereo adaptor) and have independent volume control and dedicated opamp.

I've used this with line level,  pedal level, and headphone level inputs.

[PRR]

> we have two amps with headphone outs

You may have two, but I doubt you need two.

ROLLS MiniMix is an unsexy problem solver. I'd start there.

[Krystal]

I breadboarded a "virtual earth" mixer followed by a 5532 headphone amp i nicked from the deadastronaut astrosim cab simulator. It all works just fine, it's plenty loud enough. The only hiccup is i'm gonna have to buy stereo jacks, i'm only getting audio on the left for the second.
So i could get away with a dual op amp and a couple of pots, but i'm going to go ahead and breadboard the full astrosim, and i might end up building that with a mixer in front, we'll see.
The Rolls mixers seem convenient but this is more fun !
Anyway, thanks to all of you for helping me out!

[Krystal]

EDIT:
I did try with just a couple of resistors, and it did work but was pretty quiet and had to turn the amps up quite a bit and they get hissy when you turn the up too much.

EDIT 2: messed up, sorry for double posting !

[jorg777]

EDIT:
I did try with just a couple of resistors, and it did work but was pretty quiet and had to turn the amps up quite a bit and they get hissy when you turn the up too much.

Thanks for trying it!  Worth a shot.