Korg Monotron CV Input Mod (Eurorack Control Voltage hack)

[@davidg7136]

Dude, who are you? The real master of all trades? Ive seen 3 of your vids. And you do carpentry, electronics, piano, guitar, you build synths and sequencers like whoa what else. I'm impressed. Your parents obviously invested a lot in you

[@finonomastropiero4261]

He was worth the investment. Now he is returning some of that love to the synth brokeass community. Mil gracias, wey

[@stayonpoint]

Hes secretly thom yorke

[@marcospalacios1241]

@@stayonpoint😂 we all wish this

[@marcospalacios1241]

your badass dude...i dont even know what the fucks going on...

[@MattGreerMusic]

Little Tron sounds nice when controlled like that. Good Oscillator with nice character.

[@_triff]

Awesome stuff! I don’t have a Monotron but I have a similar goal with a Stylophone x-1 I got for Christmas, I noticed on day two it’d fart out notes if I touched the stylus tip to the cv/gate out from my Deluge, ten minutes later it was in bits :) I’m just connecting both input tips to the stylus until I work out what I need to do next, surprisingly the intonation is correct if I output from the deluge at 0.7v/oct. Mathematically it seems like I need to multiply the gate and cv whereas I think my current bodge will be adding them together - which maybe looks a bit like your circuit diagram. I think I need to study both circuits a bit and have a re-watch, nice one for the info!

[@jimmy_jamesjams_a_lot4171]

I LOVE the aesthetic of those embossed decal labellers! I really preemptively jumped the gun and settled on making a much more involved project of my Monotron Delay than I should have. I chucked the enclosure as soon as I ripped the membrane keyboard off, and proceeded to very brutally desolder the goofy stereo volume wheel pot, trimmer, and a bad feedback potentiometer, actually lifting a few vias / traces in the process! I hope to just add a voltage regulator and then mount it as a eurorack module, once I fix what damages I've done and finally call it 'mine'. Now after seeing what beautiful work you've made of yours, I've decided that never again will I just throw away an enclosure belonging to something that can serve any use at all, no matter what my final plans are for it! I could have should have would have used those great DuPont connectors, and had them protrude from a little custom recessed seat in a panel for it to sit in the eurorack temporarily, OR detach it so it can go along with me on my way (maybe keep a lanyard on it for those dreaded house keys I'm always missing!)! THANKS FOR SHARING! The bus of wires to the external project box is a great method to employ when adding mods to this gear, especially when it's a sort of collectible and therefore something that you'd not want to impose upon much!

[@bobtronic73]

Thanks for sharing. I arrived at the same solution to just control via single cable connection to gate. I control it directly via software with DC decoupled audio interface outs.

[@TravisOlbrich]

Awesome video! I was able to make my own with the schematic you shared. Thanks a ton!

[@TeslaDanser]

Think I'm finally gonna give this a try. Thanks dude

[@jerrybriardy]

I wish I knew how to do all that. I have a Monotron Delay and a Monotron Duo. Both have great sounds but they could be so much more. I miss having a sequencer and ability to use a keyboard. Even the sequencer alone would be very nice. My Korg SQ1 has CV out. I think it would be fairly simple to mod the Delay and possibly the Duo to use that.

[@switchon1325]

Merci , merci , 1000 merci, i use a BC559B Philips and she a live for play

[@MangoMang]

Bro this was such a good video! Wish I knew enough about circuit boards so I could mod my Monotron Delay! You've earned yourself another subscriber 👌

[@DRPEURA]

Amazing!! Have to try this 👌🏼

[@christopher_ecclestone]

This is so good. Nice work. I killed my old Monotron trying to mod it, but this makes me want to try again and attach it to my Baby8 sequencer. Thank you for re-inspiring me.

[@finonomastropiero4261]

Can relate trying to mod this, i accidentlsy removed smd capacitor near the ground of the battery compartment. After watching the schematics i realized it was a 10nf ceramic caps. Soldered a normal Through hole ceramic 10nf cap. That shye wss intense

[@JIDEHHIGHELEMENTS]

Thanks a lot for this video ! the TRIM on monotron delay purpose is to change the shape of the LFO from "saw down" to "saw up " ... and on the original monotron it tunes the keyboard range

[@finonomastropiero4261]

Awesome ,thx

[@jeremilicata]

the intro sound.. what exactly is that? so lovely

[@extralifedisco]

Thanks! It's a channel ident I made just for these videos. I think it's a combination of a 7th chord played on a diva patch I programmed with some foley sound FX from a library called "just whoosh".

[@mirkoferremi]

Wonderful! I'm going to try this summer during vacations!

[@Doolang]

I built it! It works! Still need to calibrate a little better, but it works. Using a Beatstep Pro.

[@Doolang]

Having a bit of a time to get it to calibrate. Close, but not quite close enough. Anything I may be missing?

[@extralifedisco]

I find it's easiest to calibrate if you set up a CV sequence that jumps octaves in succession, like 1v, 2v, 3v. Then you can adjust the tuning pot by ear until they sound like octaves on the monotron. It's probably also important to use a linear potentiometer and not an audio taper one.

[@Doolang]

​@@extralifedisco Ah! I swapped the trim pot I had in there for a linear pot. Better for sure!

[@vadimzotha8628]

This is sick! I would love to build a CV adapter to Volca Modular pinpoints voltage since it’s only has a single one, which is not enough for me. Your example is very inspiring

[@finonomastropiero4261]

Man, damn volca modular. I think I broke the 1st oscillator pitch patch point, all kind of modjlation or cv sending soundd like excesive pitch amplitude from an lfo with a super rapid frecuency... I think the patch socket got bent from inside or something. Sometimes i insert by mistake theVolca modulsrs cables between the slot and its enclosure :(

[@DJ_Joe_DC]

I've hooked my monotron original up to a rakit baby 8!!! It's good fun! 👍

[@christopher_ecclestone]

I'm trying this. How did you connect it?

[@crolodon8024]

Nice delivery dude, and great video. You seem like a cool guy.

[@christopherross8358]

❤You had me at, "Lets take it apart".

[@Benadski]

You are using the pnp transistor as a diode I think. Vbe never gets close to -0.6V if you drive the gate with a 0-5V signal. Try swapping pin 1 and 3!

[@ghost_in_the_robot]

Hey brother, you are quite the Renaissance man! Master of many elements. I am hoping you can help me out, so I bought a bunch of used gear with my stimulus check a year ago and I'm stick with what I've got, so I'm trying to make it work lol... my question is about using the CV features on a lot of my gear, so I've got an iPad with AUM/Koala and other apps, as well as my desktop PC running Ableton Lite 11. My actual gear is an Arturia Keystep and Korg SQ-1 Step Sequencer with CV A and Gate 1 inputs as well as a Gate B and Gate 2 input, there is also a MIDI out and sync in/out for connecting other gear. My question to you is what piece of gear would be best for circuit bending or interfacing between the two? I assumed I'd be able to use the Keystep's CV inputs Gate/Pitch/Mod on the back to convert MIDI from the SQ-1 and send it back through my Presonus Audiobox96 USB interface for playing with arp sequences or aftertouch/mod strip on the Keyboard during live performances. Would the Korg Monotron be the best gear for this? I saw where the Deluge has CV outputs (4 total) but it's rather expensive and I cannot afford it yet lol... my only gear is a Kaossilator (Phrase one - yellow), Launchpad Mini, and some Pocket Operators.

[@extralifedisco]

Hey man! I haven't used most of that gear specifically so I'm maybe not the best to ask, but sync/clock can be the bane of many live electronic rigs. In general it's best to stick to either analog Clock/CV -or- MIDI and not try to blend the two if it can be avoided. MIDI is sometimes a pain to configure and the cables are ungainly, but it does have start/stop/reset control which is a plus. I expect the keystep will have the most robust clock options so I'd use that as the master clock and then send its clock out to the sq-1's "sync in". I believe eurorack clock and korg 'sync' are both 5v pulse, but some modules have different "PPQ" or pulses-per-quarter note. I imagine the keystep can be configured for different PPQ values, typically 1,4,8,12 are used. They should all use mono 3.5mm cables. Integrating a PC setup is harder, you can either use MIDI to control of your sequencers and then chain its analog clock to the other one, or just send an analog clock signal out the audio output from ableton and use that as your clock. I typically do this when I'm recording a song so the tempo and beats are synced with ableton's bars. I won't go into a tutorial but you just need to drop a "modular clock pulse" wav file into a Sampler and trigger it with midi at whatever clock frequency you like (this works best on DC-coupled interfaces with extra outputs you can spare for clock, but YMMV). Good luck!

[@ghost_in_the_robot]

@@extralifedisco Man, thank you so much for the well thought out and quick response. We are on the same page about the Keystep being the brains of the operation. It's literally got the MIDI control center which allows you to change the PPQ which I had to do to get my Pocket Operators synced up. So it's as simple as that, just connect to the Sync In on the Korg SQ-1. I was already thinking of using Ableton with a click track like a 16 step pattern as you suggested so that's perfect! I want to send MIDI data from Ableton to the Keystep to the SQ-1 to arrange scales using CV conversion if that makes sense. I actually have a USB to MIDI in and out cable which I could run from the Keystep to my PC to act as a bridge for the data. Do you think this would work? Thanks again for all your help. Unfortunately, the Keystep is the only real device I have which I can setup with MIDI channels to start/stop/record and have multiple tracks setup in Ableton armed to record.

[@DoctorBlankenstein]

Dr B approved

[@Ziqohth]

wow... with that pcb stuff. i inmediately subscribe.

[@awkwood7743]

Hi! Can I use a 2N3906 instead of the bc557? :)

[@extralifedisco]

Yeah I think so! may have a slightly different minimum voltage but it's only latching so shouldn't make much difference

[@awkwood7743]

Extralife nice! thanks 😄

[@MDJ5]

Who made the dope ass 80's funk tune during that reworked preamp build montage? That was juicy - woof

[@machmar]

yea true

[@extralifedisco]

Diamond Ortiz - "Cubic Z"! Good catch, meant to put the subtitle in for it, will add a card.

[@MDJ5]

@@extralifedisco thanks! also i went and snagged up a monotron on ebay after watching this. I didnt even know the existed - so thanks for that!

[@machmar]

@@extralifedisco thanks. but damn it ain't on spotify

[@MDJ5]

@@machmar it seems to be a royalty free artist, and spotify has to get their cheddar cheese!

[@stevewoywitka3258]

Thank you for this great video. I want to do the same

[@FunkHunkMusic]

Genius my dude, I’m doing this asap

[@alexanderbutler8843]

Awesome video. You're a wizard. Any advice on feeding a monotribe into a monotron? The monotribe is connected to the computer via a midi mod I purchased from USBtribe. I'm very new to all of this but willing to try wrap my head around it all but have no idea where to start.

[@extralifedisco]

Thanks! What are you trying to do by connecting them? I haven't had a monotribe apart so I can't say too much about what's possible. Looking at a quick search it looks like you can mod it for individual drum outputs, but I can't tell if it has synth patch points. The easiest thing to do would be to open up the case, look for any patch points on the PCB, stuff labelled "pitch" "gate" "VCO" "cutoff" etc, then solder some wires to those points and let them hang out the back of the case. Do the same on the monotron. Then you can use a breadboard to try connecting various combinations of wires together to see if any of them give you a desirable result. Looking at the korg schematics page, they unfortunately seem to have only included the rhythm control section in their schematics for the monotribe so it's hard to compare the synth architecture: www.korg.com/us/products/dj/monotribe/page_5.php

[@alexanderbutler8843]

@@extralifedisco Hey mate. Once I wrote that comment, I was like damn! I should have probably been more specific. I'd like to play the monotron via an external keyboard because the monotron keyboard is quite difficult for me to use. My idea was to be able to play it using computer generated MIDI notes. computer>>>usbtribe mod>>>monotribe>?>monotron. I do have a Grandmother synth so am thinking that I could create circuitry that would allow me to use the Grandmothers keyboard instead, the same as the link below. kzbin.info/www/bejne/d6epiWmGppiBjNk So inspiring to see your DIY tools, all of the drills and saws and what not. How much did you pick everything up for? Legend!

[@tubeDude48]

At 11:46, was that board a former project?

[@extralifedisco]

Yep, that's an early version of the super sixteen

[@djleozr]

Thank you so much!

[@UnterDerSonneOhUnterDerSonne]

Great work and thank you so much for sharing your process!! How did you keep its output noise so low? Where did you plug it into (meaning the device's audio output)? Any tips for reducing its noise?

[@extralifedisco]

The delay chip (PT2399) is inherently noisy, more so at longer delay settings. You can turn down the delay send but there's still a high noise floor on it. I recorded it through a Sansamp Para Driver DI, which is a guitar amp simulator and EQ pedal, into my mixer and audio interface.

[@MrFinn]

great work!

[@TeslaDanser]

Is it possible to use the existing tuning resistor instead of the new one?

[@eliofistarol8479]

How does the one 1V/octave match the internal pitch to voltage ratio of the monotron?

[@extralifedisco]

Roughly speaking, the monotron uses a 1-3v range to adjust its pitch. Theoretically that could mean it's 0.33v/oct, but I'm not sure exactly. It does sound like it's a v/oct linear scale. In practice, what I do with this mod is set up a sequence of one note across several octaves in eurorack (e.g. 4v, 5v, 6v), and then adjust the voltage scale with the potentiometer by ear until the monotron is producing octaves at those intervals. This results in a useful 2-3 octave range.

[@SouthShoreSonics]

@@extralifedisco Good to know! I can get 5 octaves of playability out of my modded Monotribes. I have modded a CV to the filter cutoff which allows me to use the ADSR of a Microbrute to control this.

[@channelite]

Really cool video. Where did you get that Kynar wire?

[@extralifedisco]

The kynar was on ebay I think - I try to use Jameco for electronics supplies since they're pretty local but I think they only sold it by 100ft lengths.

[@allourep]

This video reminds me of the money printing scene from "To Live and Die in LA"

[@notjux]

I went from not wanting or needing a Korg Monotron to both wanting and needing a Korg Monotron, but also wanting and needing to convert my entire synth collection to CV

[@jakubberan2720]

hi, would this work with original monotron?

[@shufflephunk]

hi i am looking for a replacement of the aux input on the monotron since mines broke down, anyone knows where to get a replacement component? best Larry!

[@glnnk_art]

I have a bunch of BC337s laying around, would those work the same?

[@extralifedisco]

BC557 is a PNP transistor, I think 337 is NPN so you'll need something else. 2n3906 would probably be fine, any generic silicon PNP can work as an on/off switch, specs aren't critical here. EDIT: now than I think about it, this is more like sinking current (switching a connection to ground rather than +V) so NPN should actually work fine. Though if it doesn't, you'll just find out that the gate signal doesn't do anything, and the monotron stays on all the time rather than being triggered by the gate.

[@glnnk_art]

@@extralifedisco thank you! Actually, I already finished the mod ;D I simply removed r11 on the board, which solves the pitch-gate influence altogether. It's not fully working, I must've screwed up somewhere, but it's not dead (yet) xD

[@finonomastropiero4261]

with all the knob twisted towards the gate of the monotron delay and the pin1 of the transistor , I am only getting notes ranging from G4 to F6. Compared to ableton operator plugin with same wave, G4 from my midikeyboard delivers almost an bassy A1 note, and F6 from midikeyboard is barely reaching a G4 note from opeartor :c Is there any further tip to further calibrate the monotron pitch? Changing some values? a bigger value from pot? Ableton CV instrument doesnt work because calibration process requires triggering notes from the external synth and since it is a ribbon which gets bypassed when you plug gate signal... just doesnt work. Leaving the pitch still before calibrating within the plugin mutes the oscilation when trying to calibrate itself... Its been two months with this xp. h3lp

[@finonomastropiero4261]

What was the output voltage range from your sequencer? maybe i could tune it if I boost the cv from my audio interface

[@extralifedisco]

Hey, the output range of my sequencer is 0-8V or so. Officially eurorack is 0-10v. You should be able to tune it reasonably well using the potentiometer but you may not get a "concert" pitch as the korg oscillator is not 1v calibrated. I would expect to get probably 2-3 usably tuned octaves, and then some major nonlinearity in the upper range. My suggestion would be to set up a MIDI sequence that plays a couple of octaves, like C1 C2 C3 C4 and then adjust the potentiometer by ear until you get approximate octaves. Then use a tuner to get the middle 2 in as close to perfect tune as possible going back and forth between two in a sequence in ableton. If you are not able to get octaves at all because the interval is too small, then there may be an error in your hardware - at the maximum rightward turn, the pot would let the full 0-10v CV through to the monotron, (potentially damaging it) so you should find a natural tuning range somewhere in the middle of the knob. Once you have the potentiometer set, you can use a tuner or your ear to figure out which note it actually outputs when you play a C, and then use a Pitch midi device in ableton to transpose the notes up or down so that when you play a C on your keyboard you actually hear a C on the monotron. Again, this is not really possible to calibrate in hardware because the oscillator on the monotron is not tuned to concert pitch, but you can absolutely correct for it in software. Hope that helps!

[@finonomastropiero4261]

@@extralifedisco Surely it helps

[@user-JM1967]

Are there ICs in it?

[@extralifedisco]

In this monotron? Yes op amps and other ICs for sure. In the converter? No, just discrete transistors

[@Mad4400]

What happens if your CV levels are over the 5 volt VCC max of the monotron?

[@extralifedisco]

I think you could certainly fry the monotron! It's important to wire the potentiometer correctly and always start with it in the low position and scale up until the the pitch scale sounds correct. In general, the highest voltage from eurorack is 10v and the highest voltage the monotron wants is 3v. Some of the capacitors are rated for 6.3v. So you should never send high-voltage eurorack signals through to the monotron with the voltage scale control above 40%.

[@re8et355]

Witchcraft here! I will report this to the guardians of the eight sigils!

[@planetaurdi]

hola buenas muchas gracias por mostrar tu trabajo, estuve intentando abrir el link para ver los esquemas y me da error, me los podrias pasar de alguna otra forma, saludos

[@extralifedisco]

Hmm, no estoy seguro cuál error usted ha encontrado. La esquema está disponible en PDF por GitHub aquí: github.com/matthewcieplak/monotron-cv-adapter/blob/master/MonotronCVAdapter%20-%20Schematic.pdf

[@planetaurdi]

@@extralifedisco gracias ahi va

[@RobertKgma]

Whats the pcb design software used in the vid?

[@extralifedisco]

That's KiCad! Open-source and getting better every day. I went to the first ever users' convention (KiCon) earlier this year and people are doing crazy stuff with it. kicad-pcb.org/

[@JC-xi6vn]

is it possible to use a 3.5 mm input instead?

[@extralifedisco]

Sure, you only need 2 connections so a TS 3.5mm jack would be fine, it would just be tough to fit a normal panel-mount one into the case without it hitting the circuit board. One of the low-profile SMD 3.5mm jacks hot-glued to the board might be better.

[@TravellingSynths]

Very cool! Is this something that could be used to add CV inputs to a guitar pedal? 🤔 I've got a bunch of guitar pedals I'd love to hook to eurorack..

[@extralifedisco]

I run my synth through my pedal board most of the time. Audio is easy, but adding CV input to A device is more complicated. The simplest way is probably to replace the potentiometer controls with vactrols (leds and light dependent resistors) but it's not something I've experimented with

[@TravellingSynths]

@@extralifedisco thanks for the quick reply! Perhaps something for a later video? 🙏😁 really enjoying your channel btw

[@TravellingSynths]

@@extralifedisco I've found this vactrol based passive VCA. Worth a try? kzbin.info/www/bejne/bnOyn6mJhtWifbs

[@extralifedisco]

Ah nice! Yeah have been meaning to get another VCA/LPG in my modular. Would be a nice pair with look mum no computer's super-simple AR envelope.

[@jakubjanik5146]

Hi! Do you think this mod will work with Arturia Beatstep Pro which Pitch CV Out range is 0 to 10V and Gate Ou is 12V?

[@extralifedisco]

Yes, that should be fine as the gate input is only going to the transistor's base, not through to the monotron. However be careful not to turn the pitch scaling knob past halfway or you may send a 10v pitch signal to the monotron and overvolt its input.

[@DarthGylcolious]

​@@extralifedisco​is there an easy way to limit the max voltage without otherwise affecting the signal that is under 5V? I was looking at picsynth's site with the resisters in series for pitch tuning but I had trouble understanding how to implement his solution and I'm not sure how his implementation of gate/cv differs from yours.

[@extralifedisco]

​@@DarthGylcolious ​ Picsynth's series resistor design is used for creating a keyboard with distinct buttons for each note. For this CV input you just need to scale your CV voltage down to match the monotron range. You can do that using a potentiometer as in my design or a discrete resistor divider. For example, put one 10k resistor from your CV source to the gate input and another 10k resistor from the gate input to ground. This will divide the voltage in half (because both values are equal). You can calculate various resistor ratios to divide it for an exact reduction, or you can just use a potentiometer to duplicate that circuit and make it adjustable (electrically, a potentiometer is 2 variable resistors joined in the middle). These circuits are voltage dividers. For simple voltage limiting you could use a zener diode in reverse across the gate input and ground, which will begin to conduct when the voltage exceeds its breakdown voltage (often 5.1v, but you can get them in all flavors). Google "overvoltage" protection to find many such circuits, but beware that many of of them are designed to work purely with digital (on/off) circuits rather than scalable analog voltages.

[@DarthGylcolious]

@@extralifedisco Thanks so much for taking the time to answer my question! I was concerned about having a large pot knob for the scale, as I could totally see someone who didn't know better accidentally rotating it to the max and passing through the full 10V of my microbrute's gate out.

[@re8et355]

Add a 1N4148 from VCC to the Pitch input, it will clamp the signal from going over 5v. I did so on mine. It shouldn't go anyway higher than 5v, it can accept 1V per octave but scale will be off, that is what the 100K comes in handy!

[@jacobsteel]

Great! Thank! :D

[@adamwolters]

This is great Thanks :-)

[@alarlol]

i need that betweenbox!!!!!

[@jamesprisciandaro3144]

Can the same mod be done to a monotron duo?

[@re8et355]

Yes, but not forget that he has the slider plugged in, so actually Vbias is passed to the gate at any given time. If you remove the slider, you will need a different circuitry, and the Duo has a different octave settings, that you might want a 300K variable pot instead of 100K. If memory is still working.

[@Natemasterflex]

👍