Korg Monotron

[selfpreservation]

here is the schematic of the monotron i have marked the points where i think i could add a volume control or mute switch and also where i think i could put an input for to retrigger the LFO from a drum machine trig out can someone please tell me if im barking up the right tree with this ? also would i have to trigger it via a transistor or would the 5v pulse alone do the trick?  cheers ciaran

[Gordonjcp]

Depends what you expect it to do.  You could replace R35 with a 4.7k pot and use that as an oscillator level control, with the wiper going to C14.

The LFO reset will probably work with a 5V pulse injected where you have indicated.

[selfpreservation]

Depends what you expect it to do.  You could replace R35 with a 4.7k pot and use that as an oscillator level control, with the wiper going to C14.

The LFO reset will probably work with a 5V pulse injected where you have indicated.

cheers gordon  , i would just like to be able to mute or control the volume down to zero of the internal osc as it is mixed with the external input , in fact it would be cooler if it just cut the osc when i put the jack in, so i can use the ribbon controller or a drum machine trigger to reset the lfo without hearing the internal oscillator so i can do rythmic lfo stuff say on a drum loop for instance also i would like to add a proper output pre the headphone amp as its crap can i just add a socket after the VR2a volume pot to achive this? thanks for your help

[moordenaar]

Would it be possible to make a wave changing switch in there for the vco.. I see some different ones.

[jamiewoody]

OMG i am going to have fun with one of these when i get some money saved (hopefully early 2011...).

as soon as i can, i am going to invest in some "cheap" synths, like monotron, stylophone, etc and immediately take them apart! ;-)

[Gordonjcp]

Looks like there's only a sawtooth output.  Make a comparator to turn it into a squarewave.  Add some sine LFO to the comparator setpoint to get PWM.

[jamiewoody]

so, has anybody here bought one of these and bent one yet?

[jamiewoody]

i GOT ONE! ;-)

yesterday, i frantically looked for 2 aaa batteries and could find only 2. "this will not do anything but make faint sounds...these must be dying...". i was hoping anyway.

today, after getting a little sleep, i shook the box and 2 NEW batteries fall out.  YES! so, i installed them and it worked!

so, i  even though i am still exploring this product, and cannot give it a FULL review, i will insert my first impressions here.

this thing is TINY! i mean, about the size of an altoids can! smaller than a stylophone!  it is plastic, and i would be careful with the pots. they seem durable (and will take knobs, so you can customize it!) but, are small, plastic and soldered to  the pcb...

the sound quality of this thing is amazing! i am speaking about through the tiny internal speaker. i have not tried the 1.8" jacks yet.

the filter is just magical. bandpass  i presume? the PEAK control seems to be a lot like RESONANCE! 

there is a lot in this tiny package. feature rick and sound quality are amazing! but, it just seems for $60, one could get a little better quality.

mods? maybe build it in a bigger box, with actual keys, and wire 1/4" phone jacks ? adapting down is just absurd if you  dont really have to! also, building this into a bigger box, and making the filter as part of a patch bay would so so cool! ;-)

[jamiewoody]

i just hooked up a stylophone to the input...the vcf and lfo effect it nicely!  i love this thing...more stuff i need to learn to build now! ;-)

[Gordonjcp]

http://www.synthtopia.com/content/2010/11/05/korg-publishes-monotron-schematic/

You'll probably find that interesting.  Stick it alongside the Gakken SX-150 circuit and play spot-the-difference!

It's definitely not an MS20 filter clone.

[jamiewoody]

hmmm...so the korg clone is not true to their claim, printed directly on the box..."add the legendary +ms-20 filter..."

it's still killer, noisey, beautiful!

i wonder if the internal speaker was removed if the sound would change/improve?

[jamiewoody]

i take it nobody has modded one of these yet?

i connected my stylophone to it and the monotron filters that nicely!

one thing i can't stand is, the 2 jacks are so close together, if i adapt a cable down, i cannot connect both....grrr!

i wonder why they don't make a bigger and more deluxe version, all analog?! (meaning no midi, no modeling, no usb!)

[Gordonjcp]

If you look at the output stage there's an odd thing that looks like the speaker amp has a bit more bass cut than the line/headphone output.  Oh, and it uses a four-way 3.5mm jack with the second ring being used to mute the speaker!

[jamiewoody]

i havent taken mine apart yet. i have been checking out some photos on different sites, and the circuit board is like a colouring book!

on the solder side, it is even labeled, "lfo, vco..." etc! the resistors are labeled, etc. they obviously WANT people to mod these...the first commercial product MEANT for circuit benders perhaps? ;-)

[Circuitbenders]

A lot of older Korg analogues have the sections of the board separated out with dotted lines and labelled as LFO, VCF etc. The Korg Micro preset i worked on recently certainly had, and that was from about 1978!

It certainly makes working on these things a whole lot easier.

If you look at the output stage there's an odd thing that looks like the speaker amp has a bit more bass cut than the line/headphone output.

presumably so the speaker isn't trying to reproduce frequencies it can't possibly manage?