Looking for an Active Stereo Mixer - 2 Stereo Channels to 1 Stereo output.

[pappasmurfsharem]

Hey folks.

Been awhile since I was active on the forum. The pedal building has fallen behind as I haven't really needed anything, nor had the time to commit.

Anywho...

1. I'm looking for a reasonably simple schematic to sum 2 stereo outputs to run 1 set of headphones.
2. Outputs are typical PC headphone outs.

I've seen passive ones, but I imagine that would have its own issues, so I figured it would be worthwhile to build an active mixer.

Preferably 1 volume control for each stereo channel.

My googling skills seem to be lacking because I can only find passive schematics, which might lead me to believe this is more difficult than I was hoping.

[mth5044]

You could try the blend portion of this schematic, one for left channel one for right. TL074 and some caps and resistors would be all you need unless you keep in the polarity switch. Replace blend pot with two 10k resistors, add on volume control. Good to go.

http://www.runoffgroove.com/splitter-blend.html

If you want to get rid of polarity switching, just make U2A look like U2B

[pappasmurfsharem]

If you want to get rid of polarity switching, just make U2A look like U2B

By this do you mean, literally just duplicate U2B for each channel mono channel?

Lose the fet and the feedback loop etc.

Also wouldn't that turn each stereo source to mono?


edit:

ah wait. I could Use Left Channel 1 and Left Channel two in the first summing pair, and Right channel 1 and Right Channel 2 in the next.

That however wouldn't allow me to control stereo channels 1 and 2 independantly though with a volume control.

[PRR]

You want a mixer.

You want a headphone amplifier.

Mixer passive or active does NOT matter for this application.

If it is mono, build it twice, with dual-gang pots.

Headphone amp can reasonably be one LM386 per ear.

[PRR]

[pappasmurfsharem]

You want a mixer.

You want a headphone amplifier.

Mixer passive or active does NOT matter for this application.

If it is mono, build it twice, with dual-gang pots.

Headphone amp can reasonably be one LM386 per ear.

My thought with passive would be that there would be too much volume loss.

I want two separate stereo inputs (Left and Right x2)

So as to have two separate computers/devices run 1 set of headphones simultaneously, but each device must maintain stereo and preferably have a volume for each source







***edit***
I think I see what you are saying.

Build a typical mixer, then amplify?

[PRR]

You probably need an amplifier anyway. A no-amplifier solution requires both sources to supply extra power, also fight each other. Asking for volume controls means they have to work way too hard; also leads to like 50 Ohm dual-gang power-pots, which are not a stock item.

The minimal amplifier, such as an LM386, has gain of 20 or so. This is ample to overcome the 2:1 loss incurred in mixing two sources, and leave plenty of reserve gain. In fact we probably need _more_ loss (that 10K resistor), so the volume pots don't always end up around "1" or "2".

Minor tricks shown. The '386 really needs the Bypass pin, uh, bypassed, and it really needs the 10r+0.1u network on the output or it gets squirrely with signal. We also typically want a little series resistance into lo-Z 'phones to cut amplifier hiss and limit burnout. It works just as well to combine the two functions, hence the unconventional placement of the 10r resistor.

[pappasmurfsharem]

You probably need an amplifier anyway. A no-amplifier solution requires both sources to supply extra power, also fight each other. Asking for volume controls means they have to work way too hard; also leads to like 50 Ohm dual-gang power-pots, which are not a stock item.

The minimal amplifier, such as an LM386, has gain of 20 or so. This is ample to overcome the 2:1 loss incurred in mixing two sources, and leave plenty of reserve gain. In fact we probably need _more_ loss (that 10K resistor), so the volume pots don't always end up around "1" or "2".

Minor tricks shown. The '386 really needs the Bypass pin, uh, bypassed, and it really needs the 10r+0.1u network on the output or it gets squirrely with signal. We also typically want a little series resistance into lo-Z 'phones to cut amplifier hiss and limit burnout. It works just as well to combine the two functions, hence the unconventional placement of the 10r resistor.

After sitting for a few days I just realized what you meant.

Dual gang pots should reasonably fix my issue.

What is necessary from a power perspective to run TWO 386's?

Looks like the Little GEM handles 9v so I will give that a shot, worst case I'll try 12v assuming MY 386's can handle 12v

[pappasmurfsharem]

I think this is more or less what you are getting at yeah?

[stryker]

Thanks guys. This discussion was for exactly what I was looking for.




And the result is actually better than I'd expected for the lack of cost and complexity.  I added a power switch and LED and power it with a 12V scavenged wall wart.  I cut an old double RCA connector in half and added stereo headphone jacks to the ends for the inputs.  At 1/3 volume it sounds quite natural.  There's a hiss if you leave one input disconnected, but it's not intrusive if you dial that side back.  Currently listening to youtube on the other PC while I type this and getting alert tones from this one.  Just as advertised.

Thanks so much!

Cheers! Geoff

[mth5044]

Looks professional! Well done!