This MIDI Merger / Splitter is the special 2 input 10 output thru box which I designed from scratch while not being happy with other options.

With ten MIDI output ports you set per port which input it comes from. It can go straight from input 1 or input 2 or it can go from merged 1+2. This ultimately allows zoning of MIDI ports and extremely flexible configurations and routing options. Such as you may have two independent MIDI thru boxes and MIDI Merger all on one board from two input ports. Watch a video for detailed explanation.

Microcontroller is responsible for merging capability and it's included with a PCB or Kit purchase.

There are two options for switches - micro slide type of the switch or a jumper. Jumpers are for more hardwired environment there you need the robust option that you can't move by a mistake. While slide switch option is for flexibility to choose MIDI input port. For more info refer to the picture.

It has optimized schematics for 5V and 3.3V MIDI sender devices, optimized circuitry for optocoupler to minimize false triggering and improve sensitivity. Finally it uses hex inverter with a Schmitt trigger for driving a stronger output signal. This makes it very reliable device. This is an active circuit, so it does require an external power. That’s the way it should be according to the MIDI specs.

There are two options for external power:

• To be used with a standard wall adapter 6-12V and 5.5mm*2.1mm connector. In this case a Kit comes with corresponding socket and 7805 power regulator

• To be powered from USB port. In this case a Kit includes USB->5.5mm*2.5mm cable, corresponding power socket (so you wont plug wall adapter) and doesn't include 7805. Instead of that you'll solder a jumper Pin 1 and Pin 3. Leave Pin 2 not connected. Please make sure, you use USB port or adapter with 5V output and verify it prior to connecting to the board. There are some QuickCharge USB chargers which can bump a voltage. Please, avoid using them.

Board size and an enclosure choice: Size: 7x27cm

Some of you wondered ideas for enclosure selection. Well, some kits produced here can be installed into cast cases, such as MidiThru-4 or MidiMerge_2in->5out into 1032L enclosure. It requires drilling and some patience. Other boards are just too big to go into typical aluminum case. I found it much easier to put them in between two acrylic panels cut to the size and connect them with plastic standoffs. I typically use M3 standoff 20mm and 5mm. 20mm goes on top, and has enough room to cover DIN5 sockets, while 5mm goes on the bottom. There is CorelDraw file on Github with precise board dimension and holes location.