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DIY Stereo Mixer?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author DIY Stereo Mixer?
oozitron
Any suggestions for a good sounding DIY audio mixer module?
Need four inputs, each with Level and Pan control.

thanks,
Andrew
Randy
http://www.bartonmusicalcircuits.com/stereoouts/

I've built four of them, including a double for my main rack. The headphone out is handy. I also used the headphone volume pot as a main volume pot too.

Randy
Boris_Yeltsin
Befaco Stmix and Hexmix are pretty good options.
fitzgreyve
I still have a small stock of these:

https://www.muffwiggler.com/forum/viewtopic.php?t=169457&highlight=
J3RK
Here's a schematic for mine if that's helpful. It's pretty simple, and can be tweaked in various ways. It sounds pretty good, and can drive 600R loads/headphones. There are a lot of improvements that I've made, but I don't have that schematic here. You can sum in two more sets of inputs using the same method as the first two channels to get four channels.

I'm also planning a version that uses the SSI2164 for four VC input channels, and then has servo outputs instead of AC coupling, and active panning. No idea when I'll get to it though.

heinzpeda
I'm currently working on exactly that: a 4-channel voltage-controlled stereo mixer with exponential volume control and proper panning. Also balanced line-out and a port to bypass the stereo-sum signal (e.g. to feed it into cloudssssss)

As I could not get it to work using OTA-based VCAs (mainly because I am not an electronic engineer), I just finished my first prototype around a ATMega328p and four MCP4922 running as multiplying dual-DACs (essentially digitally controlled amplifiers). I uploaded my code and schematics here: https://github.com/jhbruhn/eurorack/tree/master/stereo_mix

If you have ever built a Mutable Instruments module, my repository uses a similar structure and the same basic libraries. I can upload a PDF of the schematic though, if you're interested (although it has to get cleaned up a bit first).

Edit: It should be noted that this mixer supports both mono and stereo input (!) signals. Hence the large amount of VCAs/DCAs required (8 DCAs/16 VCAs).
J3RK
heinzpeda wrote:
I'm currently working on exactly that: a 4-channel voltage-controlled stereo mixer with exponential volume control and proper panning. Also balanced line-out and a port to bypass the stereo-sum signal (e.g. to feed it into cloudssssss)

As I could not get it to work using OTA-based VCAs (mainly because I am not an electronic engineer), I just finished my first prototype around a ATMega328p and four MCP4922 running as multiplying dual-DACs (essentially digitally controlled amplifiers). I uploaded my code and schematics here: https://github.com/jhbruhn/eurorack/tree/master/stereo_mix

If you have ever built a Mutable Instruments module, my repository uses a similar structure and the same basic libraries. I can upload a PDF of the schematic though, if you're interested (although it has to get cleaned up a bit first).

Edit: It should be noted that this mixer supports both mono and stereo input (!) signals. Hence the large amount of VCAs/DCAs required (8 DCAs/16 VCAs).


Nice!

Yeah, OTAs would work well, but I'd probably do a dual OTA config (ala Sims) for each channel, and the IC count does get up there a bit. I did a mono quad VCA+Mixer like this, and while it fit on a 3" x 4" PCB, it was absolutely packed. That's why I'm planning to use the SSI2164 for my new one eventually.

I like the digital approach. It's nice to see some different ideas like this.
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