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 Forum index » DIY Hardware and Software » Circuit Bending
Monotron mods
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Sonic



Joined: Dec 02, 2010
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Location: Toronto

PostPosted: Fri Dec 30, 2011 6:46 pm    Post subject: Monotron mods Reply with quote  Mark this post and the followings unread

Santa brought me a Monotron for Xmas. It's friggin' brilliant! santa

I want to mod for gate/cv, cutoff etc but I really want to keep it as cosmetically unaltered as possible. The best method I've seen so far is a mini-usb jack in the back. Super discrete and provides 5 pins. I've also seen a (slightly jutting out) 4-pin mini-DIN installed on the right side of the case. Any additional circuitry I'll put in a little breakout box.

I'd be really interested in any suggestions for attaching a small multi-pin connector on a small enclosure, and how to install cleanly and securely. I love my little Monotron and the idea of cutting/drilling into the case gives me the heebie-jeebies! Perhaps I should get some different types of connectors and experiment on scrap plastic? I have no previous circuit-bending / modding experience.
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umschmitt



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PostPosted: Tue Jan 03, 2012 5:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Lucky you. On the other hand, you may find handy to take away the (cosmetically unaltered !) enclosure and put the synth + mods & things in one bigger box ! I"ve also seen a wallwart mod and a one shot LFO mod, both super easy and googleable.
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MadScientist



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PostPosted: Tue Jan 03, 2012 6:53 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm planning on 'modularizing' my Monotron, which should allow me to use it as separate modules (VCO, LFO, VCF, headphone amp). This will require external components for buffering etc., and a few reversible modifications to the PCB. I only intend to use the PCB itself, while the rest of the gizmo will be put into storage. Maybe not quite what you had in mind?

- Frank.
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Sonic



Joined: Dec 02, 2010
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PostPosted: Tue Jan 03, 2012 9:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks chaps. Yes that's actually very useful. In my over-enthusiasm I overlooked that rehousing the pcb would actually be the more reversible approach. Perhaps it could even be done in a way that made the pcb quickly swappable back to the original enclosure. I have an enclosure on the shelf which looks to be an ideal size. Hmmmm...
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Cynosure
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PostPosted: Tue Jan 03, 2012 7:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sonic - I am moving up to a bigger case. That tiny case won't allow me to add much.

I already have it running on a wallwart, and I added these mods:

- Square wave with PWM and phase shifting (so the peak of the square can be anywhere from the top of the monotron's saw to just before the next saw's peak).

- Comparator clocking a 4040 to give 3 sub octaves that can be mixed in.

- Feedback loop through a diode that provide a unique sounding overdrive/feedback.

Soon I will test adding an envelope.


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blackdiscoball



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PostPosted: Wed Jan 04, 2012 7:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

I added a small mini dsub connector on the side of mine. There is just enough room and it gives you 9 pins to work with. I then had a box that connected that gave me cv and gate in. Cut off in, audio in and out, and a switch to turn tracking on and off. I could plug this box in and use all that or I could unplug it and most people didn't even know it was modified. I just recently added an LFO in which I can now control the LFO speed with an external lfo. The wire I used was a little big but it all fit. Its tight though. I plan on buying another monotron and just rack mounting that one with all the mods I did on my first plus some new ones. I mounted the Dsub on the far right (next to the pitch ribbon) by drilling a couple small holes and then filing the shape out with some needle files.
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Lorenzo



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PostPosted: Wed Jan 11, 2012 2:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Cynosure wrote:
Highpass filter - Accidental find while trying to amplify with an LM324. Has a control for cutoff and another for phase shifting the highpassed sound.


Have you the schematics for this "accidental" HighPass Filter?

Thank you very much!

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Sonic



Joined: Dec 02, 2010
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PostPosted: Wed Jan 11, 2012 6:01 am    Post subject: Reply with quote  Mark this post and the followings unread

I just noticed your post @blackdiscoball. Many thanks. That's just the kind of thing I'm interested in. I don't suppose you could post a couple of photos?
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blackdiscoball



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PostPosted: Wed Jan 11, 2012 6:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, I could try to do that.
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Sonic



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PostPosted: Wed Jan 11, 2012 8:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Merci! salut
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v-un-v
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PostPosted: Wed Jan 11, 2012 9:40 am    Post subject: Reply with quote  Mark this post and the followings unread

I must say that Korg's marketing team are a bit out of touch with the modern world. They would make a killing if they sold Monotrons through Toys r us, but all you can get there is the Stylophone- which is shit (compared to.....)

Monotron POWER! Very Happy

Which Mono did you get, Sonic?

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blackdiscoball



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PostPosted: Wed Jan 11, 2012 9:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Posted Image, might have been reduced in size. Click Image to view fullscreen.
Posted Image, might have been reduced in size. Click Image to view fullscreen. I wish I could have taken a picture of the inside but its an absolute mess and Its a pain to get closed up. I made the mistake of using wire that was a little to thick. There is definitely room to work in there (if you are tidy) but I highly recommend the SMALLEST wire you can find. The stuff I had on hand was a little to big so I kind of handy capped myself. My initial mods made it so that if you didn't have the box attached it worked 100% normal, most people didn't even realize I had added the extra dsub on the side. I recently added control over the lfo and now if you don't want the box attached, you need to plug in a small dsub that I have two pins wired together, if not the lfo doesn't work. This has kind of been my test monotron. If I did it again I would just do cv and gate in and no other extras. I might do that at some point but the next thing I would like to do is rack one up with all these mods for the modular synth Im working on.
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v-un-v
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PostPosted: Wed Jan 11, 2012 10:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Nice! Very Happy

It's just a shame the breakout box isn't as pretty. Wink Smile

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Sonic



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PostPosted: Wed Jan 11, 2012 10:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Wow, you must have done quite a job to fit it all in @blackdiscoball. Would you use the same type of connector again if you made another modified case?

@v-un-v I got the original Monotron. The mrs claims she got it for $25 + shipping, although this offer seems no longer to be available. I would probably have bought a couple more at that price. I hear crazy deals on these appear every so often. I'll probably pick up the whole set eventually. I'm envisioning a mini battery-operated analog performance setup made up of a collection of little boxes. Something instant and fun. A percussion box, synth(s), mini sequencer, mixer etc.

This video really got me thinking. I love the mini trimpot baby-8.

http://www.youtube.com/watch?v=5SbXBVfZMSc
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blackdiscoball



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PostPosted: Wed Jan 11, 2012 10:24 am    Post subject: Reply with quote  Mark this post and the followings unread

I would definitly use the same connectors. Its a tight fit but it gives you a lot of options and I like the option of having it work as normal with little extra attached.
Quote:
Nice!

It's just a shame the breakout box isn't as pretty.
At least its labeled! Sometimes i spend a lot of time on casing and graphics, other times I just starting soldering and drilling holes, this was the a case of soldering and drilling holes, (and filing as was needed to fit the dsub in).
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v-un-v
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PostPosted: Wed Jan 11, 2012 11:26 am    Post subject: Reply with quote  Mark this post and the followings unread

I'd be well impressed if the breakout box was as beautiful. But what has already been done is excellent. Very Happy
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Lorenzo



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PostPosted: Wed Jan 11, 2012 2:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

v-un-v wrote:
I must say that Korg's marketing team are a bit out of touch with the modern world. They would make a killing if they sold Monotrons through Toys r us


ahaha Laughing !!!

Korg kicks out a plethora of plastic beasts: elecribe (es-1 !!!), Kaoss Pad, MicroKorg...
that are plastic case toys playable like real instruments!!! Wink

What about Roland engineers??? Twisted Evil

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Cynosure
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PostPosted: Wed Jan 11, 2012 5:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Lorenzo wrote:
Have you the schematics for this "accidental" HighPass Filter?

It is here. This is just an updated version of my previous schematic. I forgot the protection diodes for the 4040.

After looking into it a bit more, I think that it is actually a modified comparator. There is a passive highpass filter added to the end that acts kind of like a pulse width modulator more than a high pass filter. There is also a pot that adjusts where the newly formed squarewave is in relation to the original sawtooth. So the square can be anywhere from on top of the peak of the saw, to just before the peak of the follow saw.

It is U1a in the schematic. Maybe one of the experts here can explain it better. I honestly have no idea how it does what it does, but it is very useful and sounds good.


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Lorenzo



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PostPosted: Thu Jan 12, 2012 1:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Cynosure wrote:

It is here.


thank you very much! I will try it!

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Cynosure
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PostPosted: Fri Jan 13, 2012 6:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Here is a video clip showing the waveforms. I have no idea how it does it, but it sounds cool Smile

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Paradigm X



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PostPosted: Tue Feb 28, 2012 2:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

there was an amazingly compact modded monotron posted at muffs recently, http://muffwiggler.com/forum/topic-53496.html

i think you need to be logged in to see the pics. amazing tho. Im such a klutz.

the tiny midicv thing looks a good idea too

http://www.midi-hardware.com/forums.html?section=prod_info&product=MINICV

been meaning to mod mine for a while but not got round to it.
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Cynosure
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PostPosted: Tue Feb 28, 2012 3:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

That one is very cool considering how much he managed to cram into the original case.

I have finished up most the soldering on mine and I am working on the case now.

I added a simple active lowpass filter to the squarewave and sub oscillators, as well as an envelope that controls the filter cutoff.
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Sonic



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PostPosted: Tue Feb 28, 2012 7:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Wow. Thanks for posting this Paradigm X. Really useful to see this. Current plan is still a DB9 connector with a breakout box, but I think I'm avoiding the job as I'm afraid to hurt my poor little Monotron! I picked up a Dremel type thing last week for this kind of job, as my power drill is perhaps a bit brutal. Especially if I forget to switch off the hammer drill setting!

#edit:

p.s. I should say thanks blackdiscoball for the DB9 connector idea!
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v-un-v
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PostPosted: Wed Feb 29, 2012 5:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Does anyone know what to do to modify the volume pot so the travel is far less? So say, rotate by half, then you get full volume from nothing.
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richardc64



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PostPosted: Wed Feb 29, 2012 4:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

v-un-v wrote:
Does anyone know what to do to modify the volume pot so the travel is far less? So say, rotate by half, then you get full volume from nothing.


Perhaps the pot's taper needs to be modified?

http://www.geofex.com/article_folders/potsecrets/potscret.htm

Skip past all the stuff about how they're made down half the page to "Tapering."

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