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.


  1. First of all: Thx a lot for this post! When i was looking for this, i always ended up at this youtube video:
    But having the LFO still available is great! And having more switches and stuff on it makes the monotribe even look better! ;)

    I have questions to the text on the first picture: Do i need the green vca out? Or do i need to put a resistor somewhere? On the other images i can't see anything else than the wire and the swith. Whould be great if you can explain this in a little more detail. Thx!

  2. Thanks for being the first commenter on my blog, I was hoping it would eventually get some action.

    I think the VCA out, I'm glad you pointed it out, I think maybe you could send it to a jack, and do the same for all the drum voices, which is a mod you can find elsewhere, and then you'd have separate jacks for the "synth" and each "drum" instead of having it all mixed to the one usual output jack. I'll have to give this a try and report back. I did not create that image I ganked it. I guess the series resistors here would reduce the volume a bit. You could take jacks directly off of the VCO (labeled here "wave outs") but, unless you're doing some kind of modular thing I don't see why you would want that, without the filter and VCA, just raw square or triangle or saw waves or whatever. Back to your question.

    For the purpose of the Synth Voice Mute Mod I called it, you only need to ground out (mute) the VCO pads as I described in the post. In the picture they are the ones labeled "Wave outs!" Hopefully it will be clear now if you re-read the post. Yes the terminology is probably a bit confusing with different names being used for the same things.

    As I get around to the drum outputs and probably now VCA separate outputs I'll be posting more about that. Thanks for the question.

  3. Thank you monkeyxx, this definitely save me weeks of trial and error. I think these vco waveout and vca out pads will spin off a few more interesting mods in addition to the Synth voice mute, which is excellent btw.

    If one VCA pad for the rhythm out and the other for the synth voice, I think routing these VCA outs might yield effective for feedback and drum to VCF mods....

    1. Wow I hadn't even considered that. If you look into my other posts on this blog, you'll see I have a fairly crude but functional separate Drum out and VCA out mod posted. I am going to have to plug the drums into the filter and see what happens! I love filtering drum machines. So obvious, that I didn't even think of it, thanks!

    2. No problem, however, I believe this mod may come at the cost of either choosing between your dedicated 1/4" drum out mod or filtering the drum out. As the rhythm out to VCF will have the drum signal moving out the synth voice VCA out...

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  5. Just wanted to say thanks for posting this mod. I used your pictures and was able to get the mod installed no problem. I can verify that a sub mini DPDT switch (1a) works for this mod. I didn't have a drillbit for anything bigger. I also positioned the switch in the middle of the case (between the ribbon and the gate time button) which seemed like a good spot. Other than that I followed everything you did and it worked! So thanks again. I would add that I did this mod primarily so I could filter external audio-- but the ability to play the filter is such a great thing, as you mentioned.