MUFF WIGGLER Forum Index
 FAQ & Terms of UseFAQ & Terms Of Use   Wiggler RadioMW Radio   Muff Wiggler TwitterTwitter   Support the site @ PatreonPatreon 
 SearchSearch   RegisterSign up   Log inLog in 
WIGGLING 'LITE' IN GUEST MODE

Help Modding a Korg MS20 Synth
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page 1, 2, 3  Next [all]
Author Help Modding a Korg MS20 Synth
WytchCrypt
Hi all, I've just bought a Korg MS20 Desktop semi-modular and the PC board has multiple labelled patch points for adding additional inputs and outputs to 1/4" jacks. My electronic skills are basic, I can solder and make cables but nothing much more complicated than that. I could use some help with a couple questions.

1) What type of wire should I use to connect the PCB points to the 1/4" jacks? I know it should be insulated but is there a recommendation for what gauge I should use? Also, is rigid copper wire better than flexible multi-strand wire for this or does it really make any difference at all?

2) Most of the PCB patch points are very simple in that they have 1 point which is positive and another labelled Gnd. However, 2 of the patch points have 3 connection points, "VCA Jack In, VCA Jack SW, VCA Jack Gnd" and the other is "Ext Sig In VR C.W., Ext Sig In VR Center, Ext Sig VR Gnd". Can anyone tell me why the patch point would have 3 connections rather than 2? Also, I would assume these would require a 3 prong stereo jack though I don't really know what kind of signal in they would be expecting to process.

I'm buying a bunch of mono 1/4" jacks to add access to these cool additional I/O points (VCO1 Mod In, VCO1 Out, Filter 1 and 2 High and Low Pass Outs, and VCA out) but wanted to get some additional info before I start the project.

Thanks to anyone who can help me out here nanners
gelato
i don't know about the ext sig in stuff but maybe the marking on the PCB are meant to suggest that you use a switched jack so that when nothing is plugged in to your new vca in jack the vca is still connected to the internal envelope or whatever.

if you don't know what a switched jack is its basically a regular jack but it has three connections. when nothing is plugged into the jack what is connected to the switch part of the jack will be connected to the tip part of the jack and when a cable is inserted the connection will be broken. this way you can have a synth patched to make noise before you put a cable in with out sacrificing the modular functionality.
qfactor
^ that as well as, if you get your mono jacks, take a close look at them as most of the time, the "mono" jacks would have 3 lugs (3rd one being the switch as gelato described above! thumbs up
WytchCrypt
Thanks for the clarification. The 2 wire access points don't worry me but I'm wondering if I could damage the unit if I wire up those 3 output wire access points to the 1/4" jack incorrectly?
raveboyy
"Ext Sig In VR C.W., Ext Sig In VR Center, Ext Sig VR Gnd" woul probably be for an external signal input potentiometer`s 3 lugs
WytchCrypt
raveboyy wrote:
"Ext Sig In VR C.W., Ext Sig In VR Center, Ext Sig VR Gnd" woul probably be for an external signal input potentiometer`s 3 lugs


Makes sense. Any idea on how I can determine what ohm value of pot I would need?
raveboyy
no idea...they don`t include some documentation?
WytchCrypt
raveboyy wrote:
no idea...they don`t include some documentation?


Nope. It's clearly an "undocumented feature" meant for those want to do their own modding. There is some discussion in Korg circles that a "modding kit" may be offered at a later date, but so far the only official word from a Korg USA rep is:

"Although we do not encourage users to modify the MS-20M Kit beyond our design specifications, we are aware that there are very technically capable users who enjoy this type of activity. To facilitate connectivity without degrading the factory appearance, we have made a provision on the front panel through the inclusion of additional holes covered in removable blanking plugs for such use. Please be aware that any modification to the product will void the warranty and that any modifications are performed at the owner's risk."
raveboyy
I think you should have a look for MS20 schematic, the would sure help a lot...

edit: here
raveboyy
the schematic says that the external signal in volume pot is 1M, if i read it right (1M0)
WytchCrypt
raveboyy wrote:
the schematic says that the external signal in volume pot is 1M, if i read it right (1M0)


Fantastic! Do you see anything about the other 3 wire access point for VCA In and what value pot it would be looking for?

Thanks we're not worthy
raveboyy
"VCA Jack In, VCA Jack SW, VCA Jack Gnd" refers to a jack ...

I don`t know what type of jacks do you have but:

Jack In is where the tip of inserted jack plug contacts the jack socket
Jacks SW is the contact which disconnects when you plug in the jack
Jack Gnd is the sleeve

Little bit hard to explain without showing it...take your jack socket and inspect it closely..you will find out

Or link a picture of jacks you have and I`ll show you, but it has to be the very exact type you really have..
WytchCrypt
raveboyy wrote:
"VCA Jack In, VCA Jack SW, VCA Jack Gnd" refers to a jack ...

I don`t know what type of jacks do you have but:

Jack In is where the tip of inserted jack plug contacts the jack socket
Jacks SW is the contact which disconnects when you plug in the jack
Jack Gnd is the sleeve

Little bit hard to explain without showing it...take your jack socket and inspect it closely..you will find out

Or link a picture of jacks you have and I`ll show you, but it has to be the very exact type you really have..


Makes sense. Here's a shot of the jacks I'm looking to purchase for this project. So is the proper VCA jack a simple stereo jack?

Thanks!

sonicwarrior
WytchCrypt wrote:
So is the proper VCA jack a simple stereo jack?

No, I suggest Mouser No. 502-112AX aka Switchcraft 112AX.
raveboyy
He is right, you need Mono and switched (i.e. with a switch)
Like mouser 502-35PM2A...but these are a little bit hard to solder, because they are made from quite a thick metal. You have to set a higher temperature on your soldering iron.

I like these. But depends whether they will fit into your build..have a look at the datasheet for the dimensions.
WytchCrypt
I'm looking at the mouser 502-112BX switchcraft for both applications. Correct me if I'm wrong, but it appears this jack can be wired for both the simple Positive-Gnd connections I need to make and the 3 wire VCA In, SW, & Gnd.

http://www.mouser.com/ProductDetail/Switchcraft/112BX/?qs=sGAEpiMZZMsU zhEcHltCuTFgK4jOO9kP
sonicwarrior
The 112B is a "Double open circuit." = stereo jack. No switch there.

You want the 112AX. Trust me. I use these myself.
(They are mono with a switch for normalisations)

Edit: You can see them here in action:

raveboyy
WytchCrypt wrote:
I'm looking at the mouser 502-112BX switchcraft for both applications. Correct me if I'm wrong, but it appears this jack can be wired for both the simple Positive-Gnd connections I need to make and the 3 wire VCA In, SW, & Gnd.

http://www.mouser.com/ProductDetail/Switchcraft/112BX/?qs=sGAEpiMZZMsU zhEcHltCuTFgK4jOO9kP


Yes, that's right...the 'switch' can be connected or not...depending on the application.

Try to google what is the 'switch' for...you will have to understand that anyways for different situations....

EDIT: correct me if I'm wrong but when i found part number 502-112BX at Mouser, it says switched..so that should be the right one...
WytchCrypt
sonicwarrior wrote:
The 112B is a "Double open circuit." = stereo jack. No switch there.

You want the 112AX. Trust me. I use these myself.
(They are mono with a switch for normalisations)


Sounds good. Mouser & allied electronics are out of them and won't be shipping for at least 3 weeks. Amazon has a retailer that has them in stock but wants $6 a jack (over 3x what mouser sells them for!!!) and I need 10. I did find an online retailer called DigiKey that will sell them for $2.28 a piece so think I'll go with them.

Thanks!
sonicwarrior
raveboyy wrote:
EDIT: correct me if I'm wrong but when i found part number 502-112BX at Mouser, it says switched..so that should be the right one...

You cannot always trust Mouser. Trust the manufacturer (Switchcraft) instead which has graphics showing that the 112BX is a type IV = stereo jack (double open circuit) while the 112AX is type III =mono, switched (single closed circuit):
http://www.switchcraft.com/Documents/Jack_Schematics.pdf
112AX: http://www.switchcraft.com/ProductSummary.aspx?Parent=67
112BX: http://www.switchcraft.com/ProductSummary.aspx?Parent=72
WytchCrypt
sonicwarrior wrote:
The 112B is a "Double open circuit." = stereo jack. No switch there.

You want the 112AX. Trust me. I use these myself.
(They are mono with a switch for normalisations)


Before I pulled the trigger and bought these I took a look into my MS20 to see what kind of jacks it was using in the patch bay. I couldn't tell if they were specifically 112AX's but there were that same style of closed box switch bodies, not the open type I was originally planning to use (which are commonly used on guitar jacks). I'm curious, are the closed box types better at blocking interference or static pickup from nearby components than the open guitar style?

Anyway, the only online supply house I could find that wasn't out of stock on the 112AX's was Digi-Key. They were a bit more expensive than Mouser ($2.28) but I don't have to wait 3 weeks thumbs up
sonicwarrior
WytchCrypt wrote:
are the closed box types better at blocking interference or static pickup from nearby components than the open guitar style?

No, it's just plastic which won't stop interferences or static pickup.

It just protects the jack from shorting with nearby components (other jacks or pots) and looks better.
WytchCrypt
sonicwarrior wrote:
WytchCrypt wrote:
are the closed box types better at blocking interference or static pickup from nearby components than the open guitar style?

No, it's just plastic which won't stop interferences or static pickup.

It just protects the jack from shorting with nearby components (other jacks or pots) and looks better.


Got it. Thanks thumbs up
Scott Willingham
WytchCrypt wrote:
Hi all, I've just bought a Korg MS20 Desktop semi-modular and the PC board has multiple labelled patch points for adding additional inputs and outputs to 1/4" jacks. My electronic skills are basic, I can solder and make cables but nothing much more complicated than that. I could use some help with a couple questions.


Congratulations!

Just a heads up -- you should be aware that some of Korg's patch points require simple PCB modifications in addition to wiring up jacks or potentiometers. For instance, the "EXT SIG IN VR" points require the removal of a zero-ohm resistor that shorts the CW and CENTER points. I imagine the same applies to the VCA JACK IN/SW points too. The VCO1 Mod In point looks like it requires one or more resistors to be added to the board to scale the input.

It sounds like you may not be comfortable with surface-mount modifications, so you may need to get someone to help out in those areas.

Hope this is helpful information.
Eloc
raveboyy wrote:
the schematic says that the external signal in volume pot is 1M, if i read it right (1M0)


Just from this labelling: "Ext Sig In VR C.W., Ext Sig In VR Center, Ext Sig VR Gnd", I don't think that 1M pot on the schematic is the same one that is part of this mod. The one on the schematic is part of the feedback loop on an op-amp (it doesn't go to ground), whereas "C.W." [clockwise], "Center" [wiper] and "Gnd" [ground] would imply that it was a voltage divider/attenuator probably wired between the signal and ground or possibly between a DC voltage and ground (but less likely) with the wiper effectively selecting from somewhere between those two. I would imagine that 1M would be too high a value for this; I would think something like 100k may be more appropriate. Also, if it is a signal attenuator, I would think an "audio/log taper" pot would be more suitable... either way, you could buy both linear and log and change it if the curve of the pot doesn't feel right (i.e. nothing much happens for like 1/2 the rotation of the pot).

Someone else may chime in and confirm or refute this claim...
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page 1, 2, 3  Next [all]
Page 1 of 3
Powered by phpBB © phpBB Group