4 x 1 Mono Mixer--A Confidence Builder

Readers: If you'd like to build the project featured in today's post, please go to PCBWAY's Community pages--gerber file (main board); gerber for jacks board, front panel gerber, a 3D model of the dual pot (WRL and Freecad formats), KiCAD project/pcb/schematic/library files and a B.O.M. are here.  

You can also help out this site immensely by checking out PCBWAY using the link here. Thanks!

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I've DIWHY'd many projects lately that don't work due to dumb mistakes and I thought, enough! I'm going to lay out and build something easy, useful and practical. 

Everyone needs more mixers right?

The "EZ MIX" was really easy; it took me an evening to lay out and about a half hour to build: a simple 4 input AC/DC unity gain active mixer in 6HP Eurorack format.

The star of the show: dual concentric pots; you get Eurorack's "fit every damn thing on the head of a pin" paradigm without needing extremely tiny hands to turn the knobs.

           

                              

I laid out a footprint for the concentric potentiometer in Kicad and 3D model in Freecad:  

                                                 

Piece of cake.

The project used 3 boards: front panel, jacks panel, and main PCB, centered around a single dual op amp IC.

Everything on the main board was through-hole; other than triple checking sizes, legends, and drills there wasn't a lot to go wrong. 

To remain old school: JST connectors were used between the main board and jacks board.

Main board

jacks board

Front panel....

Off it all went to this blog's honorable sponsor, PCBWAY....

Happiness: new boards from PCBWAY

Zoom, printed circuit boards were back, I gathered up parts from the junk box and got building.

I was fearful things wouldn't line up, thankfully they did....

Everything worked first time ("WFT")--pots went from no volume to full volume when turning them clockwise, audio signals got mixed, legends on the front panel were correct, and most all silkscreens on the boards were accurate.

One (big) mistake--the "Redstripe" (negative voltage) silkscreen callout was on the wrong end of the Euro power header. This silkscreen error was fixed on the 9-12-24 revision I uploaded to the PCBWAY community.

The only SMD part for the project: I added a 0 ohm 1206 resistor between Out1 and Out2. That way if I reused the 3.5mm jacks board in another project the 2 outputs could be independent of one another.  

But in the spirit of this build I soldered the 2 output wirepads together--who needs SMD?

 Finished!

So much fun I made two of them...

Overall, it was great to kick back and design then build something really easy. 

Getting stoopid from time to time is fun....but now it's back to debugging, dealing with cryptic IDE error messages, C++ that won't compile--all the usual things. I can't wait.