"I can hardly believe no one knows about this already. It is possible to control an MS-20 from a V/Octave keyboard or MIDI/CV converter without a special interface. If you don't believe it, try it . .

When I first got my MS-20, I noticed that the filters don't track the keyboard at all. I plugged the keyboard cv to the filter cv in, but then the filter tracked the keyboard slowly in the lower octave, then went screeching off in search of tweeters to kill! I soon realised that the filter was tracking exponentially. I looked at the schematics and sure enough, both the VCO's and the VCF's have exponential converters on the modulation inputs. (You can tell this is the case, because the synth also goes radically out of tune when you plug the kbd cv to the TOTAL input, and wind up the MG / T.EXT knob in the FM section.)So, if you stick a V/OCT input into the modulation inputs and adjust the MG level for correct scaling, it all works and the filters track too.

Here's how you do it:

1. Plug the performance wheel into the keyboard cv input (middle, right) to disconnect the keyboard.
2. Plug the V/OCT cv from your MIDI/cv converter or another synth into the Total jack (top left).
3. Plug the s-trig. from your MIDI/cv or synth into the MS-20 trigger input.
4. Play a note on your MIDI keyboard or the controlling synth, and adjust the MS-20 performance wheel until you get a sensible pitch.
5. Adjust the VCO mod. levels until playing an octave on your MIDI (or other synth) keyboard gives an octave out of the MS-20. Then adjust the MS-20 performance wheel to coarse tune the MS20 and use the tuning pot to fine tune it.
6. The filter mod level pots adjust filter tracking in the same way.

You lose use of the performance wheel on the MS-20, but that's not a big problem if your MIDI/cv converter or your other synth has pitch bend. You will need a v-to-s trigger converter (i.e. the MS-02 Interface) to control the MS-20 from synths without s-trig. outputs, but they're simple to make (two resistors and an NPN transistor, plenty of circuits posted elsewhere).

I don't have the MS-20 in front of me, so apologies if the names of pots and jacks are not exact. Believe me, it does work!"

(from Steve Ridley)

Somebody else added:

"Beware of one thing... the VCF's are twice as sensitive as VCO's so that you must bring the VCF's mod pots to about 5 where as you would have the VCO's mod pot to 10. I think this can confuse some people the first time they fool around... Actually, if one wants good VCF tracking one has to be careful in trimming..."

>One of the things that still annoys me about the MS-20 is that all modulation of VCO frequency affects both
>oscillators equally. It would have been so easy for Korg to have two sockets for VCO modulation (like they did
>for EG trigger and VCO cv) instead of one. Without an extra socket, you can't control VCO detuning with an EG or
>the MG, you can't use the ring modulation for those spacey noises, you can't bend one VCO against the other etc.

"For your information, that feature comes standard on the unit!

Try patching the mod/pitch bend wheel to the VCO-2 cv IN. It is just under the Power switch/volume knob. Try that, hit that seemingly useless wheel and viola! - instant ring mod. gratification.

Also try patching any of the direct envelope outputs into the VCO-2 cv input; excellent for pitch envelope ring modulation. Note: there are two separate CV control inputs, one for VCO-2 cv 'as mentioned' and the other to control both VCO's 1 and 2."

"Every time I encounter situation with the MS-20 where I wish I could do two things with one input, I usually solve the problem by simply using a two to one 1/4 inch adapter (I use the same adapter to split outputs as well). So in the case under discussion I'd say try COMBINING the wheel and keyboard cv's- it should track but I'm not sure if it will track accurately (there's no knob for the VCO-2 input and if it's not set up for the HZ/octave of the keyboard we're in trouble).

Meanwhile, back to the subject of mods.... an earlier poster wondered about VCO outputs, I'd love to know about this myself. Also has anyone thought about replacing/upgrading the incredibly noisy VCA?"

. . and you can use the junctions (a.k.a. multiples) on the MS-50 and MS-02 to 'split' a signal into 2 or more outputs, conversely.

"The 'total' and 'freq' input jacks on the MS-20 and MS-10 which control the oscillators' frequencies are scaled in V/OCT.

The only problem using these jacks with a V/OCT MIDI/cv converter is that the EG1/EXT. frequency modulation knob is not stable enough to allow the tuning to be set and have it remain stable. The synth runs from 1 V/OCT when the knob is about three quarters turned.

However, the knob is stable when cranked up full, but this results in the synth expecting an input of 0.8 V/OCT or so."

Another MS-20 fan added:

>Do you not also lose modulation possibilities? For example, if you use the 'Total'
>jack, don't you lose the ability to use the Modulation Generator for VCO FM,

Yes. But you could still route this to the VCOs using patch cords.

>and wouldn't the signal from the MIDI to cv convertor be routed to the VCF's
>also instead of the MG?

>Using the 'Freq' jack wouldn't you lose the use of EG-1 as a modulator?

Yes. But you could still route this to the VCO's using patch cords.

I see what you're getting at (that the V/OCT cv takes up a VCO control input, whereas the Hz/V cv does not), and I admit that the machine is really intended to be run by a Hz/V converter. I wanted to clarify that running it via a V/OCT converter is possible."

Korg themselves would of course recommend the MS-02 Interface for this purpose.

"Anyway, one simple 'mod' that requires no work: insert a cable only halfway into the cv-in for LPF or HPF. This way the EG won't be disconnected when using external cv control! So an external cv signal controls the filters just like tweaking the 'cutoff frequency' knob. This'll often sound better than when the EG is disconnected."

>I really missed PWM on my MS-20, but lazy as I am I bought an MS-10 to get it. There would probably be a market
>for someone doing these mods to the MS-20. It's definitely possible.

Ok, I have done that some time ago on mine. I didn't want to drill extra holes, so I decided to replace manual PW by PWM (ccw: fixed width, cw maximum LFO PWM). Its just two resistors, a wire and the cutting of a pcb connection. Everyone who has service docs could easily figure it out.

Anyway, I wouldnt do it again (though it works like intended). I miss *manual* PW a lot now (it is fun to modulate it real-time by hand), and with PWM I have to decide for one, hard-wired, PW starting point. (I always hated this approach on Roland synths: either PWM *or* manual PW. The main reason that Jupiter strings cannot reach Oberheim and Prophet strings, IMO)

I will recondition it to the original state some time. If only these PCBs weren't fixed with thousands of pots ... modding Korg MS synths is a pain!

>I'm messin' with my MS-20 and decided to bite the bullet and try and figure out what the hell the button on the left hand side does (the little black one next to the mod wheel).
>I know it's assignable and I know it puts out something in the range of +3 or so, and it's probably a trigger of some sort but I have no idea what *use* this is.

"Well, what I've done with it was that I had some drum sounds coming through the ESP, but the trigger threshold level was kinda iffy. It'd trigger one of the envelopes, but barely. It'd play along just kinda peeping around for a while, then I'd have the (momentary switch) trigger out patched into the second envelope, to fully trigger it (usually at a certain point in the song). That's what I did with (the switch) anyway."

An interesting use for it I've found, is to trigger EG-1 to control VCA-2, and dynamically introduce pitch and/or filter modulation, governed by a noise source. Good for those underwater or space sequences in your next Discovery Channel/Apollo 8 documentary soundtrack. Here's the patching:

VCO 1 & 2: off (zero on the mixer)
VCO Frequency Modulation: both zero
VCHPF Cutoff Frequency: 0
VCHPF Peak: 0
VCHPF Cutoff Frequency Modulation: both zero
VCLPF Cutoff Frequency: 4
VCLPF Peak: 9
VCHPF Cutoff Frequency Modulation - MG/T.EXT: 8

EG-1 Delay Time: 2
EG-1 Attack Time: 7
EG-1 Release Time: 5

EG-2 Decay Time: 3
EG-2 Sustain Level: 5+
EG-2 Release Time: 4+

(Other controls are irrelevant.)

Patch Panel:

Momentary Switch to EG-1 Trig In
EG-1 Out to VCA-2 Control Input
Pink Noise to VCA-2 In
VCA-2 Out to Total In

"Being a cute little cheap synth, the Korg was bought by a lot of poor musicians. It's getting real popular again. It ain't built like no Moog. I suggest to all Korg MS owners that they pop theirs open and look at the power supply. There are two voltage regulators which supply 15v and -15v to the board. These regulators are held to a heat sink.....WITH NYLON BOLTS. Mine had sheared due to harsh impacts suffered in the past decade and also probably due to hundreds of hours of uptime heating up and corrupting the plastic bolts. When mine died, what had happened was that the bolt on the -15 unit had sheared and there was like a hundredth of an inch twixt the regulator and the heatsink. Regulator heated-heated-heated, and finally just started letting voltage thru the system. First thing to go was the gate controller on my Kenton; second thing to go was the opamp governing trigger behaviour on the HADSR and keyboard. Unit went to the shop where everything looked fine... We left the box on for a couple hours to burn in and "...hmm smells like burning chips..." by the time we tracked down the regulator problem it had fried about 6 or 8 components board side.

Nuff said? If you aren't skilled enough to do this yourself go to the shop. There's probably other things that were made to die inside this valuable little beastie. I've had my upgraded and replaced the 1/4" jacks with Switchcraft ones . ."

"I also found a little cheat to make the MS-20 gate triggerable. Feed your gate into the External Signal Processor and voila... trigger out to trigger in and you're good to go!" (note: the gate must go down after each note or else the Processor won't trigger.)

There is no Din sync on the SQ-10, but it's a simple matter (for someone with a soldering iron) to build a converter output of 1 opamp (a 741, say) to convert Din sync output to trigger the clock of the SQ-10. (This is how I used to sync mine to Din sync, and hence, to MIDI through my Din-to-Midi sync converter).

As some of you may already know, the MS-20 can work in OCT/V mode. Use the VCO input instead of CV in. Adjust the potentiometer (VCO section, EG1/EXT) to around 8.5 - 9.2.