DIY Stereo Mixer?

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oozitron
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DIY Stereo Mixer?

Post by oozitron » Sat Nov 30, 2019 12:29 pm

Any suggestions for a good sounding DIY audio mixer module?
Need four inputs, each with Level and Pan control.

thanks,
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Randy
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Post by Randy » Sat Nov 30, 2019 12:40 pm

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.

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Post by Boris_Yeltsin » Mon Dec 02, 2019 12:03 pm

Befaco Stmix and Hexmix are pretty good options.

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Post by fitzgreyve » Tue Dec 03, 2019 3:52 am

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Post by J3RK » Tue Dec 03, 2019 6:56 pm

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.

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Post by heinzpeda » Wed Dec 04, 2019 10:16 am

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/tre ... 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).

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Post by J3RK » Wed Dec 04, 2019 1:29 pm

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/tre ... 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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