Brian Tuley

I have modified Ken Stone's schematic to suit my own needs. I have omitted those features that I will not have room for on my panel. My build will be for a 4 input mixer with pan and volume pots for each of 4 inputs. There will be 2 stereo outputs and 2 inverted stereo outputs as well. I will also need to revise this schematic so that the mixer is AC coupled. I will not be using this for DC signals, so it is best to AC couple the circuit so as not to introduce any DC offset during usage.

Bill of Materials. I plan to build this on a perf board. I've also included the AC coupling components.

This is the initial breadboard build. I had to place an order for 4 x 50k log and 4 x 50k linear pots. I'm also awaiting a shipment of 47pf capacitors. When these arrive in the mail, I'll place them and I should be able to debug very quickly.

Top view. on the top of the breadboard there will be a row of eight 50k pots. Four will serve as volume control, and four will serve as stereo pan control. I have AC coupled the four inputs and the two outputs as well.

Pots have arrived. All ducks are in a row. 4 x logarithmic pots are used for the volume control, as human hearing tends toward a logarithmic curve. 4 x pan pots are linear in that I want the pan control from left to right to be linear and likewise, even. I'm still waiting for a shipment of capacitors and then I'll be ready to test the unit against my modular system.

All components have arrived to complete the breadboard build. Upon initial testing the outputs were mute. Tracing through the circuit with an oscilloscope probe revealed that I neglected to ground each of the TL072 op amps at pins 3 and 5. With the non-inverting inputs to each op amp grounded, functionality meets expectation. With my solder iron heating up, its time to move this circuit onto a perfboard.

Top view of perfboard. I have tested the 1st input and non-inverting stereo outputs and all is working great.

Rear view of perfboard. I still have a lot of pots and jacks to wire up before placing the board into the face panel.

I have modified a YuSynth panel template to serve my needs with this module. There are L and R non-inverting outputs as well as L and R inverted outputs.

Here I have used masking tape to fix the template onto the blank panel. Next I will drill holes in the the locations which are accurately marked.

Using a drill press I have forged holes for the pots and jacks to fill.

Mixers have a lot of jacks and pots to deal with.

I have mounted the perboard to 2" brass standoffs. Cable ties are used to keep the all those twisted pairs nice and neat.

Side view.

Alternate side view.

All done. I have tested the module and everything is working as expected. Performance in linear and there is no noise introduced. I am very pleased with this mixer. Next I'm going to try to add text to the face plate with label maker.

My label maker arrived. I'm using white on black 3/8" tape. The tape has a slight reflective glare to it, but overall I'm happy with the results. It looks better than the paint marker and I should I ever get a mill, I can still remove the labels. I find that the bold face font works best for viewing. I plan on using the label maker on future face plates as well as on my previous paint marker panels. The paint marker wipes away with lighter fluid, so I can pretty all my DIY modules as well as this one.