Korg MS20 LP/HP Filter

[Ciaran Haslett]

Here's one to keep Tabby busy

First the schematic.  I reworked it for use with an LM13700.  There's more cuts and links than are probably necessary but I wanted to have my power rails identical to other layouts I'm working on.  But hey.....I managed to get The Hulks meat and veg into the bottom left so the extra effort is totally worth it!

Make sure to read the notes carefully.  The original MS20 has 2 identical circuits in series.  The notes explain how to do this OR use one layout and switch between HP or LP.

A word on power.  I've been getting into the Eurorack thing lately.  For those that don't know...Eurorack is basically a standardised modular synth design.  Power/connectivity/rack size etc is identical across the format.  So that's why I've chosen not to include a power supply with this layout...I'll be using a Eurorack solution.  You could however build any of the charge pumps on the main site as a separate daughterboard and see how it goes.  I may try that soon for a desktop pedal style build...but for now I'll be working on it for Eurorack.

The schematic (and original Korg design) calls for +/-15V.  Eurorack provides +/-12V.  You could try a basic divider with 9V to give +/-4.5V...but I'd assume the headroom would make it unusable...or cool!

Anyway I plan to build this soon but thought I'd share now with all the current interest in filters and synths.  It's my intention to build the HP and LP separate, so omitting the switch.  If anyone would like to give the layout a once over I'd appreciate it.

Cheers

[Hozy31]

Cheers Ciaran. Wow i certainly have an ever expanding build list now. Had a good laugh at the Hulks meat and two veg.

[tabbycat]

is that the hulk's meat and veg, or is that what they call 'the luck of the irish'?.

many thanks indeed for your layout and explanations/suggestions, ciaran. comprehensive.

i was just (earlier this evening) trying to decide which of the two ms20 layouts i had already found to do (both here at em http://electro-music.com/forum/topic-43085-50.html ). one rather long and thin, and one not so long but rather wide. neither small stompbox format friendly. this is peachy perfect in all directions and your timing is impeccable.

doesn't look too painful re cuts and links. multiple double-links and hundreds of tiny jumpers are the hard ones. flat resistors eases the pain too. looks nice.

will use rocket's 9v/18v switchable 7660 layout for power. i think it puffs out more or less 15v happily.
http://4.bp.blogspot.com/-kp82eYtM8iA/Vo2paywwB-I/AAAAAAAAALY/g51nz9z3YbI/s1600/Switchable%2BOnboard%2BPower%2BV2.png
http://tagboardeffects.blogspot.co.uk/2016/01/switchable-onboard-power-918v.html

have only got BC558B (not BC558C) for the trannies. is that a deal breaker?

have also got BC560C, which are what are specified in the takeda ms20 layout (in em post above)?
or 2N3906 which hoyager reported using successfully in their build of clacktronics layout for the schmitz ms20 (on page 1 of the same em thread).

dammit, i'll try anything and report back what works. may be a week or so but it's must-have, so soon.

[Ciaran Haslett]

Hahaha....no such luck here

This charge pump would suit better as it provides bipolar power without modification.  If you use 1N400x diodes instead of the 1N5817's you should get much closer to +/-15V.  AND you can sub the IC for a 7660S if that's what you have.  Just bridge the cut between pins 1 and 8.

Seems to me that any small signal transistors would work in this so I reckon use whatever you have.  I do remember reading that they should be pretty well matched but I can't find where I saw it...so feck it..bang in whatever you have.

And just thinking on mods.  You could replace that 10K I mentioned with a pot and play around with the LEDs...silicon/germ assym etc.  Kinda like the Tube Screamer drive control.  This would alter the way in which the Resonance peak clips.  Not sure how useful it would be...just thinking out loud.

[Ciaran Haslett]

Build with confidence.  This bad boy is VERIFIED!



I had to breadboard the transistors as the ones I have are BCE.  I'm currently waiting on a bunch of 558's.  I also used the BB to test the switching since I don't intend to use it that way.  Just wanted to verify it for anyone who does.

Also, thats Mark's Bipolar Voltage Converter I linked to above.  Again, I don't plan on using it but just confirming it'll work for anyone who does.

So Recap...

Self Oscillation.....................Check
Switching HP/LP....................Check
Clipping Options worth it?......Hell Yeah Check

Spent the last hour swapping LED's, Ge/Si diodes, mosfets.  Each have a definite timbre and well worth experimenting with.  Oscillation starts pretty much at noon on the Res pot.  I upped the 10K and lowered the pot to 50K so it now only goes mental on the last 10% or so.  YMMV.  As a test, I fed it a drum loop in HP mode and cranked the Res to near full and dropped the cutoff to the bass drum..  This distorted the bejesus out of the kick but left the rest mostly intact.  The different flavours I got from swapping diodes was immense.  I'll need to play some more and find some to settle on.  Even using diode strings all made a difference!

All in all...it's a really good sounding filter than can go complete bonkers if you want it to.  Enjoy!

[Travis]

Nice work Ciaran! What instrument(s) are you planning on using this with?

[Kinski]

Very cool. What do CV1 and CV2 pots do?

[Ciaran Haslett]

Cheers Travis.

It's going to be part of a modular synth I'm planning on building, Eurorack style.  My hope is to do it all on vero.  This was a simple way to get started.  It's just a 2 pole filter with pretty extreme feedback so it should work equally well with a distorted guitar.  Haven't tried yet to be honest but I will and report back.  I've a bunch of FOH jobs on over the weekend so it'll be Monday before I get near it again.  I must test it with 9V as well.

Next on the cards will be a couple VCO's and LFO's then more exotic stuff like envelopes, S/H.  Haven't been this excited to build something in a while! I'm planning to build it all into a suitcase (both lids) for ease of transportation with a MIDI to CV card so I can connect any MIDI enabled USB keyboard for performance.

Just have to learn to play keys now  I'll keep calling back with new layouts/progress reports as they happen.

Cheers lads

[Ciaran Haslett]

They're just for mixing multiple CV inputs to control the cutoff frequency.  Currently left off my build as I ran out of mixing resistors

[Kinski]

Ah, ok. So CV inputs would be LUG 3 of both those pots then?

[Kinski]

Or perhaps that what "Pitch" is?

[Ciaran Haslett]

Yeah missed note sorry.  CV in to lugs 3.  Pitch is just another CV input.  It's labelled to match up with the terminology of VCO's with a "Pitch CV" that tracks with key presses.

[Travis]

That's a great idea Ciaran and I'm also interested in the MIDI to CV card. My girlfriend has a nice little controller with weighted keys but I think she'd have more fun using an analog modular approach rather than the soft synths she's got. And ya know, it would be a fun project for me to build.

I'm not knowledgable about synth stuff, so I will be leeching as much info as possible off you

I might as well start with this board here. Got any suggestions on conveniently rack-able enclosures?

[Ciaran Haslett]

Sorry man.  Festival season over here...busy as hell.  I try to draw the layouts B or BB size so they will suit someone who isn't interested in the Eurorack thing.  But, Eurorack modules don't have enclosures, just faceplates...so I don't really need to worry about it other than the fact it needs to fit in a rack.

As for the MIDI/CV card...this caught my eye recently.  You can buy the AT pre-programmed too.

[tabbycat]

Ciaran Haslett wrote

Build with confidence.  This bad boy is VERIFIED!

hey ciaran, many thanks for the verified update (and the original layout). i actually built the board and power daughter the week you posted, even had delusions of beating you to the call. concentration not been up to soldering recently. but soon... it's on the list. so your nod of approval is much appreciated.

[SonusFluxa]

Built this a few days ago and I'm loving it! Thanks for the layout.  It's going into my eurorack that I'm slowly building up, a mix of pcbs/kits and 100% diy vero modules. It's still just the bare board right now, but I'll post a pic of my panel when I get it finished.

How's your eurorack project going? If you're interested, I've got some odd LFO layouts that I'll be putting in my rack (voltage controlled, weird shapes).

Earlier this year I filled a 2x94hp rack entirely with modules I built on vero, but the whole thing is running off of a 9v brick a la castle rocktonics. I'm sure some of that stuff could also be converted to euro pretty easily.

How are you going about your power supply? That was the only thing I bought fully built so far, as I don't want to muck up the most important part of my rack.

[Ciaran Haslett]

Glad you're enjoying it!

I seen your post a while back....outstanding work man!  It's exactly the kind of thing I'm after.

My efforts slow enough to be honest.  Lots of gigs/FOH/parenting etc kinda got in the way (as life does) but seeing this pop up again has rekindled the excitement.  I did draw up the VCO-1 but haven't got anywhere near it yet.

I made my own PSU based on Doepfers, only I used a mains transformer (just because I had one laying around) and split the rails from there.  Loads of filtering and regulation and its good to go.  Looks like shit but it works fine lol.  

Going this way has the benefit of allowing me to install an IEC socket in the side of the case and have the entire PSU mounted internally.  That way, no matter what venue you go to, if you forget your power lead they will always have a kettle lead laying about....and not always a laptop type supply haha.  Basically I'm trying to minimise the reliance on odd/bespoke parts....cos I've a head like a box of frogs sometimes lol.

I bought a load of Molex connectors and sockets.  That's how I intend to marry the modules to power.  Works great.

I'd love to see your layouts man!  You had some tidy bits of gear in that rack of yours.  Did you ever do a video demo?  THAT, I would really like to see!

[heuermh]

Hate to say me too, but I'm on a similar path.

My boys and I put together two racks with the Tiptop Audio Z-rails, one with our own power supply and banana jacks for 9v CMOS wierdness, and one with Tiptop's power supply for DIY eurorack stuff.

https://foxtonemusic.com/shop/modular/tiptop-audio-z-rails/

I'm curious what you guys have done for the output mixer, and if you added any guitar <--> modular modules.

[SonusFluxa]

Ciaran: The power supply sounds awesome, I'd love to see pics!

I haven't don't a demo vid yet but now that there's been mention, I'll try to get one recorded in the near future. As for the layouts, I'll start a new thread.

Heuermh: Always glad to hear someone else has jumped on the weirdo synth train.

For the mixers in my 9v rack, I used two of the 4 channel into one 2 channel TL072 mixers posted a while back on the main page. Works well enough, but does give me a bit of distortion depending on what I send into them.



For my eurorack rig, I just got my PCB for the Barton musical circuits 4xVCA/mixer. I've also done a vero layout of his guitar input, which has some interesting features.

[traktop]

Just something related to the ms20: