29.11.11

Korg MS-20 pix


between the two VCO's is the sync switc.
on the VCA 'panel' is the EG2 switch and the VCA pot.
would like a matching knob for that one..


where the grey stage tape is, is where the old holes are. temporary fix, no doubt.
(lots of space inside, need to come up with extra goodies to fill those holes.)
new jacks are located in a more convenient spot.
not that i'm using them in the picture, but i could.

Korg MS-20 mods/schematics

okay, so i got hold of the schematics and board layouts here.
if you want to reproduce some of these mods, you'll need them, as i already screwed the bugger back together, so no handy step-by-step pix.


EDIT: HERE'S SOME NICE WORK ON THE NEWER MS-20 MINI!

1. patching out the VCO's.
this is easy - just tap into the right points on the waveform selector switches.

as you can see, the white noise on VCO1 is the same white noise source that's on the patch bay, so to me there's no real use in having that twice.


VCO2 is a little more difficult to read, but ok.
the bottom throw i highlighted is the straight saw signal. easy.
next: IC6 turns that saw into a square or pulse wave, depending on the state of its non-inverting input.
as you can see,  the second pole of the selector switch connects that input either to ground or not. when connected, you get a square wave - if not, pulse. that's why the square and pulse waveforms are on the same point, aka the output of the opamp.
therefore it is impossible to tap into a square and a pulse wave at the same time here - the same opamp is responsible for both, and it can only do one or the other. it's basically a hardwired version of the PW pot on VCO1.

the four logic gates on the bottom here are your ring modulator (there's an error in this factory schematic!), and the output goes from R65/66/67 straight to the top throw of the selector switch.

notice that the square/pulse from VCO2 gets used to drive the ring modulator through D8 -
the second pole turns the pulse wave into a square wave when on the Ring setting.
however, the ring gets fed the pulse wave (same opamp output) when in pulse or saw mode as mentioned in my previous post. so out the jack comes.

+++

listening to the waveforms on the new jacks, i noticed the volume drops if the same waveform is selected as the VCO out to run through the internal filters. (listening to saw out patchpoint with saw selected on VCO, for example.)
i might want to buffer them, but for now, it doesn't really bother me.
might depend on the circuit they get patched into, though.

2. sync switch
hard sync is not all that hard to implement.
you need to reset one VCO (slave, preferably the one with the higher pitch, so VCO2) with every cycle of the other VCO (master, here VCO1).


the trick is around D4 and D7.
in this case, you want to pretend that D4 (VCO1) is attached to Q10 and Q11 (VCO2), overriding D7.
you cant't just make that connection, because D7 will then also override D4, and that's no good.
so we throw in a fake D4 substitute.
a wise man on a nice forum mentioned that it would be best to use shielded wires and connect the shields to ground to avoid the oscillators locking when their frequencies are close. you run the risk of them syncing through stray wire capacitance even when the switch is not engaged.
i took his advice - never even tried otherwise, but it works beautifully.


3. EG2 to VCA switch
this, to me, is a big one. i feel it expanded the possibilities of the synth a lot.

slightly edited schematic:


there's a length of wire conveniently running across the board, connecting the EG2 output to the VCA in.
i believe it's labeled 'No.4', but don't quote me on that - anyway, it connects to R125.
if you snip that wire and put in a switch, you can now defeat EG2 control of the VCA.
i also put an extra jack on the side of the EG, as an EG2 0-5v output.

of course, you need to plug some other voltage source into the 'initial gain' to open the VCA, or else it'll be dead silent. but at least now you can choose whether or not you want EG2 in the CV mix!


4. VCA floor pot
since i felt it was a bit of a waste to always plug something (mostly the mod wheel) in the initial gain jack, i decided to hardwire a mod wheel duplicate into an initial gain duplicate, freeing both the input and the mod wheel up for other uses.
it was almost as easy as copy/pasting, except that i didn't need the negative voltages of the mod wheel.



i kind of hustled the schematic around a little, to show what i copied.
i left out the new EG2 jack for clarity.
everything still connects to the same spot, the CV mix node.
i copied the initial gain input (diode + 1M pulldown), and one half of the mod wheel.

this way, the initial gain jack, EG2 and the floor pot all play together nicely.
you can modulate through the initial gain jack, on top of a floor pot drone that'll last until the wall runs out of juice.

if you ever think of offering this mod to people, some credit would be nice.


23.11.11

Korg MS-20

i was getting jealous of the great sounds Wieter gets out of his MS-10.
so i went over the hurdle and bought me an MS-20, hah!
the thing sounds fucking unbelievable..

got it relatively cheap, compared to today's prices - because it had mods done to it (aka extra holes in the top), and i also got a small refund because the Ring Mod wasn't working.
insert new 4011, and voila: full working order!

some genius had decided to bring out all OSC1 waveforms, to make the output patchable.
great idea, if you drill the holes on the Right Hand Side over by the bay, dumbass.

played around with it for a while, and started thinking about what i would like to add, featurewise (hey, it already has holes in it.)

VCO1:
- i'm keeping the tri/saw/square outs.
- do away with the noise (that's on the patchbay anyway)
- and i'll be adding PWM instead.

VCO2:
- i'll go with three jacks: saw, square/pulse and ring mod out.
square and pulse are on the same point.
the ring mod uses the PW wave of osc1 against the square wave of osc2, but if you switch to saw or pulse on osc2, it gets fed the pulse wave instead of the square. so bringing out the ring mod would offer even slightly more tonal options.
- thinking of a Sync switch, using VCO2 as slave.

VCA:
- already added a VCA floor on a pot.
this is basically a hardwired implementation of the 'initial gain' patch, just leaves both the mod wheel and the initial gain jack free for extra modulation.
- putting EG2 on a switch, so i can defeat EG2 and just use the floor pot.
VCA modulation all you want through the init. gain jack, WITHOUT EG2 interfering! 
- EG2 gets a jack out. it's the line controlling the VCA, aka the 0-5v envelope. could be useful.


when all that is done, i need me a voltage mixer..
pix soon.

10.11.11

Silver Apples support

False Friend had the honour and pleasure to support Simeon/Silver Apples on his Antwerp date.
in my eyes Simeon is an electronics pioneer, not so much for the stuff he built but for what he did with it.
Silver Apples were way ahead of their time, introducing basically the same material Stockhausen used - see below - into a pop/rock setting, to great result. i'm not too hot for the new stuff (blame the evolution of Eurodance), but the records that feature them as a duo (Simeon + drummer Danny Taylor, rip) are mindblowing. check those out if you haven't already.

i was totally happy with the set we did. we should play more often, hah.
pictures here.