Korg_Monotrons

When these first came available I think they were about $50 each and I bought each one as it came out. They are one of the coolest things I think Korg has ever produced! They only came out with these three in the Monotron line and are no longer produces as far as I know. But you can still find them on ebay and at various

used music equipment outlets. They each have audio input and output (headphone) jacks and can be connected in series to increase their overall capabilities. They also are battery powered and have an internal speaker, but obviously sound much better if outputs are routed to a nice amplifier. These just beg to be modified. If you open one up, the PC board has labeled pads you can solder wires to and route to headers to connect to the 'outside world'. I have completed this process with my Monotron (the white-framed one) and connected it to my Korg mini sequencer to play with it. The sequencer essencially replaces the keyboard although the keyboard (actually a ribbon controller with keys printed on the plastic covering it). These are monophonic (hence the title "Monotron") so you can't play chords on one, however if you connect them in series you can play 'chords' by touching the keyboards of the separate Monotrons. If you can find any of these they are really worth grabbing if you can get them for around the $50 price that they were originally. There is quite a following of these online with mods galore if you are interested in doing any.

This is the first one to come out (2010) - simply called the monotron.
It is a very basic single voice synth with just the controls you see. This is the on I've modified with a female 8-pin header connected to most of the internal PCB labeled pads. Here's a link to the project:

Just take a look at the photos and you will see how the PC board is labeled in such a way as to make it almost foolproof to execute mods on these. Another BIG plus is that Korg made the full schematics available for all three of the Monotron models! This makes it much easier to know what you are doing or what you want to do with your mods. I chose to just bring the labeled pad functions to the header and then implement mod ideas on a protoboard outside the Monotron just using jumpers and whatever components I needed.

Next to be released was the monotron Duo (2011).
It increased the VCO count by one with some configuration choices available between the two oscillators. It also has the great VCF, same as the monotron.
Now people had the capability to try these two connected to each other and see what new sounds they could produce. The batteries last quite a while when you play with these... I've never actually run a set down while experimenting with the monotrons(I use the 1.2V rechargeables).

The last of the monotron series to be released was the monotron Delay (2011).
This is easily my favorite one! I love the reverb / feedback effect it produces, and along with the other two you can really get wild with some really 'out there' sound effects. Believe me, you will not be able to put this one down for quite a while if you can get your hands on one!

These last two monotrons were produces the same year so I'm not entirely sure of the order of release of these two, but as I remember it this was the release order.

There was another synth released which was kind of a monotron hybrid... called the Monotribe, it was a hybrid of the monotron and Electribe groovebox. I only mention it here because it is kind of a monotron. I've never had the opportunity to play with one so really can't comment on it.
There is another Korg mini-synth series that followed, called Volca.