The simplest modules you can build but they will be the ones you use most often because each modular synth needs at least a few of these.
This will probably be the shortes article on this website and the simplest of projects but I just thought I'd mention these multiples here because recently I built a few for my Eurorack case and some newcomers to this hobby might not be aware of them. They are so useful to have in your setup.
Multiples are passive devices because they do not require any power source. They just split up signals so you can have 'multiple' sources of the same signal (hence the name). You put the output of an audio or CV source into one of the sockets and then you can tap that signal from the other sockets to turn one output into multiple outputs.
There are two versions of these that you can build.
The straight forward passive multiple that consists of just a number of 3,5mm female sockets connected together. Usually it's between 8 to 10 of these underneath eachother. You can add a switch in the middle so you can split it into two rows of half the number of sockets. That way you can use if for more than one signal source.
Then there's the switched multiple. That's the same idea only now each socket has a 2-way switch next to it, with a middle off position. Each switch has their left pins connected together underneath eachother and the same for the right pins and the middle pin of each switch goes to a female jack socket. (see schematic image below)
This will allow you to put one of two signals on each of the outputs or switch that output off. This can be very handy in live settings where you want to switch between two sequencers for instance. So you need toggle switches with a middle off setting for these. At least, that's the best way of doing it. ON-OFF-ON switches. You can use ON-ON switches but then you can't switch anything off.
There are also buffered multiples like the one in project number 25 on this website but they require opamps so they are not passive in any way.
Here's a schematic overview of the multiples. The length of these is dependent on the space you have available on your panel. For Eurorack it's usually 10 in a vertical line for a passive mult or 8 if there's a switch in the middle. And for a switched mult it's usually also 10. For Eurorack that is. For a Kosmo sized panel there's room for much more sockets.
Here is a picture of the mults I made and built into my Eurorack case. This was rather hastily done on a sunday afternoon so it looks a bit rubbish (so what else is new) but that doesn't matter to me as long as it works. My switched mult (on top) uses dual pole switches because that's all I had so there's some redundancy built in because single pole switches are really all you need.
The bottom one has a switch in the middle so I can use it as one 8 socket multiple or two 4 socket multiples.
If you want to build Buffered Multiples with opamp buffers then you can go to this article here.
Buffered Multiples are often used to connect more then one VCO to a 1V/Octave signal, because with those signals it is important that the voltage on the input is reproduced accurately on the outputs, in other words it's not dragged down however many VCO's you connect to the multiple. Passive Mults with many things connected to them can draw the voltage down a bit wich would de-tune a VCO.
Okay that's all. Just a simple little item but one you will have to build at least once. The good thing about them is they need no circuitboards and you can use off-cuts of panel material to build a few of them.
Okay, until the next one!