Thursday, January 17, 2013

MONOTRIBE - Synth Voice Mute Mod

I picked up this idea somewhere, but, the tracks on the "wave outputs" inside the Monotribe are too tiny and delicate to cut and interrupt with a switch.  So instead there's the "hack" idea of just sending them to ground, to mute them, using a 3PDT switch.  So that's a three pole switch, one for each waveform, and when you switch it "on" it sends each of the three VCAs separately to ground.  There are many ground pads on the PCB you can find them by using a multimeter from any known ground point that's obvious, like a screw, to your suspected point, and testing for continuity.  Link that to the other poles of your switch.

I first did this mod so I could use the Monotribe as a filter.  The stock Monotribe mixes in its own synth voice with the audio input, and there's no normal way to defeat it.  When you turn off the synth voice on the sequencer, it mutes the Audio In as well, kind of killing the fun of the idea of using the 'tribe as a filter.  In comes the soldering iron... When you mute the oscillators, the synth voice is muted, so you can run whatever audio you like into the Audio In jack and still go through the filter, and the LFO still works too.  Nice.  The catch is I think you have to have the synth voice running a pattern, even though you can't hear it, or else the whole thing gets muted.  Not a problem really just turn the unit on and it's got that stupid pattern in it.  Which brings me to the only issue I've found with my mod: You have to turn the Monotribe ON with the VCA not muted.  If you have the VCA switch set to mute (ground), the Monotribe will hang on a blinking light and will not boot up.  Just turn it off when you're turning it on ;-D.

But I found that even when not using the Audio In, when you mute the VCA, you can set the filter resonance really high and just "play the filter!" which cool.  It opens up even more room for high pitched, weirdo, alien, video game, serial killer soul stealing type noise making.

So yes, between the MIDI mod and this one, I'd recommend doing both for more fun and features.

My switch location was not optimal...I had to hack at the case a bit, the bottom half, to get it back together again.  So as always, drill carefully and with a plan, if you can.

I've been told this mod can be done effectively with an SPST switch also, if you don't have a 3PDT or don't want to use one.  That would save some space inside.

UPDATE (6/5/2013) --  It turns out the filter does key tracking, so, if you program in some kind of melody on the ribbon, you get a tempo synced step filter!  Pretty cool, I just wrote a song with this, using my DX7 into the Monotribe filter section.  It also turns out that the envelope generator is still active, so, your "invisible" melody will fade up, or saw down, or do nothing (square) depending on which envelope you select, and how many separate notes you play in.  You can also sort of "play" the cutoff in a small range on the ribbon instead of the usual cutoff knob.  If you want a static filter with no stepping or sweeping, you can just hold down a single note for the duration of the monotribe's sequence length, and set the EG to square.

I'm not disappointed in the filter, but, it doesn't sound like the MS10 filter demonstrated here  At lower ranges it seems to get "quiet" instead of "fat."  It's also kind of a noisy situation, even compared to the DX7 hiss.  So yeah that's a little disappointing overall, but, the syncable step filter and LFO filter, envelope sequencing makes up for this, for sure.  This is a lot of fun, you've just got to try it!!

This $5 computer software for your MIDI enabled Monotribe, looks to allow adjustment of key sync, and many other things "under the hood."  I'll be trying it out.

A Word About Stripboard

All of my posts so far have been stripboard, sometimes known as Veroboard (a company's name for it,) layouts.  Stripboard layouts blew the doors open for my DIY habit, when I realized a small pile of the stuff could make me literally thousands of different simple circuits, e.g. guitar pedals, for a very low cost, on a whim--assuming a stock of common parts.  Now I'm branching out into using it for stereo equipment, and soon, professional audio equipment.  Turret board, point to point, and perfboard are other similar construction methods not using pre-fabricated Printed Circuit Boards (PCBs).  I still find it very helpful that companies like,, and many others offer PCBs for more complex projects or those requiring space efficiency, or for those requiring absolute lowest noise by using a large ground plane, for all of which stripboard is not always the best option.

If you are a beginner or are unfamiliar with working with stripboard, and wish to try, please take a look at my link in the right hand column of this blog.

Wednesday, January 16, 2013

The Mighty Mini Monotribe by Korg, now with MIDI Input and Output, by me.

I've seen lots of people doing this and all sorts of mods on the wonderful Korg Monotribe.  I currently own one only, but, as soon as it comes up again on Hello Music for sale I'll probably add a second.  And then complete the dream by adding a decent drum machine and sequencer of some sort, and a x0xb0x which will be sort of the crown jewel.  I just love what people do when they run different verses, choruses, leads what have you from a variety of sequenced boxes like these, and I want to try it.  Add some effects and have even more fun.

So you can buy the horribly overpriced MIDITRIBE kit from Amazing Machines, or you can buy the nicely priced one from Altitude909 on the Gearslutz page he posts on, or, well, you can hack one out yourself, which is the option I chose (using generous help from Altitude909).

I had trouble finding the right connectors, I wanted 180 degree 5 pin panel mount DIN connectors, and the only ones I could find were from Preh and I had to pay a lot to have them shipped overseas.  You can be a lot less picky about this than I was, I was just set on having this type of jack on the side of my Monotribe, solidly mounted, ready to use with any standard MIDI cable.

Regarding construction, the header pins, the little protruding wires inside the white connector on the main circuit board, are a bit tight for soldering, I fanned them out a bit, but the joints were solid and I'm not worried about them bumping together either... it's not beautiful but it works.  Some electrical tape crammed in would have been insurance.  You could always do me a one-up and buy a jumper that fits the header and come up with a better layout.  Or perhaps solder from the back of the board instead for a little extra room.

Other than that it was all pretty straightforward, once I sussed out the errors in my layout, which is now VERIFIED.  I went with the adequate but not rock hard method of mounting the tiny circuit to the big PCB using double stick tape.  The strength of the wires gives a bit of mechanical hold as well.  I'm sure a fancier mounting scheme could be devised.  Or I could break out the heavier duty double stick.  It's fine for now.

I haven't truly delved into using this new feature, but I will say, it's exciting to hear those goofy ribbon pad sequences getting played out of my Alpha Juno, a synth with body and fatness, along with the pitch LFO.  And of course it's exciting to play Actual Notes! on a Real Keyboard! into the Monotribe and laugh jeeringly at the little ribbon controller.

Here's my stripboard layout and photos of my installation.  Total cost to me or you: $Not much.