PCB pattern for René Schmitz "late" MS20 VCF?

andrewF · Posted: Tue Dec 04, 2007 4:58 pm Post subject:

Takeda San has a good version of the MS20 filter with very compact PCB.
I built it a few years ago and reckon it is very good.

how`s this for tight?

http://www.aleph.co.jp/~takeda/radio/MS20clone2E.html
Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

v-un-v · Posted: Tue Dec 04, 2007 5:19 pm Post subject:

yeah- seen that before. nuts! Smile

Clack · Posted: Wed Dec 05, 2007 1:45 am Post subject:

ericcoleridge · Joined: Jan 16, 2007 Posts: 889 Location: NYC

andrewF · Posted: Wed Dec 05, 2007 4:49 pm Post subject:

I do remember, the transistors used are very generic I have used them in all CGS circuits without problems.
The 2sc and 2sa pinouts are ecb , as in - you are holding the transistor, pins down, writing side facing towards you and reading from the left -
emitter, collector, base.

You could try mounting the transistors on the copper side, looks ugly, but plenty of space.

Thanks for the info on evolution of Korg filters, is it known when Korg changed to the OTA design? I might crack open my MS20 one day and have a look, though I suspect it is the early version.

ian-s · Posted: Wed Dec 05, 2007 5:41 pm Post subject:

Clack · Posted: Thu Dec 06, 2007 2:12 am Post subject:

is there any circuits showing the discrete ota? or was it a 'secret design' covered in black stuff ?

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

ericcoleridge · Joined: Jan 16, 2007 Posts: 889 Location: NYC

Scott Stites · Posted: Thu Dec 06, 2007 11:11 am Post subject:

The original Korg 35 schematic was generously given to someone, I can't recall who by K. Ishi (IIRC), and this person either has or had it on the web. I've got a copy of it somewhere; it could probably be found with a bit of Googlery.

In the meantime, a redraw and quite extensive analysis can be found in Tim Stinchcombe's doc about it here:

http://mysite.wanadoo-members.co.uk/tstinchcombe/synth/MS20_study.pdf

Cheerios,
Scott

frijitz · Posted: Thu Dec 06, 2007 3:11 pm Post subject:

Scott Stites · Posted: Thu Dec 06, 2007 3:24 pm Post subject:

It's surprising that the HP response would only be 6 dB - it's a very agressive filter, and has a pretty fair auditory "scoop" to it.

Wasn't there some version of a four pole S-K filter that Korg did? Seems to me there was. Seems to me like one of the "Greek Letter" Korg's had one. Delta or Lamda or Sigma or something like that. Maybe EFM copied one - can't quite remember why I think that may be the case.

Scott Stites · Posted: Thu Dec 06, 2007 3:27 pm Post subject:

OK, yeah - it was the Korg Delta.

frijitz · Posted: Thu Dec 06, 2007 7:57 pm Post subject:

Scott Stites · Posted: Fri Dec 07, 2007 5:56 pm Post subject:

frijitz · Posted: Fri Dec 07, 2007 7:16 pm Post subject:

frijitz · Posted: Sat Dec 08, 2007 3:18 pm Post subject:

Scott Stites · Posted: Sat Dec 08, 2007 3:46 pm Post subject:

Hi Ian,

Absolutely. At the point where resonance becomes fairly apparent with a signal present, removing the signal will leave the filter self-oscillating. In fact, I use that for effect now and then by just cranking the input level all the way down.

Cheers,

frijitz · Posted: Sat Dec 08, 2007 4:50 pm Post subject:

ENDIF · Joined: Jul 14, 2006 Posts: 138 Location: Reno, NV

@ Ian

You mention using an LED to introduce a bit of dirty clipping into the waveform.. the Blacet 2100 oscillator does this:
http://www.blacet.com/VCO.html

The output is labeled as VC Wave, and if you click the image of the module in the link above, you get some nice shots of the board itself. The LED's (he uses two) that are used are in the middle rear of the board, one resister in from the outermost trim-pot:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

First thing I built, sounds fantastic.
My favorite is the VC Wave, especially in the bass range.
Meaty. =]

frijitz · Posted: Sat Dec 08, 2007 7:20 pm Post subject:

frijitz · Posted: Sat Dec 08, 2007 9:29 pm Post subject: mp3

Here is a demo showing a few of the sounds this system can generate. A SAW wave is input, and the input amplitude and frequency as well as the filter frequency are fixed as the resonance is set at different values, starting at the high end and coming down in steps. Scott wasn't kidding, you get all kinds of strange and wonderful sounds from this. Note that there are several regions of chaotic behavior.

Very Happy

Ian

fich001.mp3

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fonik · Posted: Sun Dec 09, 2007 6:20 pm Post subject:

frijitz · Posted: Sun Dec 09, 2007 8:25 pm Post subject:

Scott Stites · Posted: Sun Dec 09, 2007 11:10 pm Post subject:

Yes, that sample is exactly "it" Ian! If I set the frequency of the sawtooth to a fairly high pitch, I can use the cutoff control, starting at its lowest settings, to dial in what I can only describe as "subharmonics" - they are pitched lower than the fundamental, but it's an entirely different thing than just a simple sub-oscillator. As the cutoff is dialed close to and above the fundamental frequency, the timbre becomes more "reedy", and higher than that, almost bell-like, but with a reedy quality.

On my dual module, I put in a three-position switch to control how the cutoff controls work. The first position allows me to set the cutoff of both filters separately. The second position allows me to control them in tandem. In other words, if filter "A" is adjusted, filter B will track that. If I adjust filter B, it sets the offset from filter A's cutoff control. So, I can select a fixed spread, and move that spread around with filter A's control.

The third position allows filter A's cutoff to control both filters' cutoff frequency just like the second position, but the filter B position will now move the filter A cutoff frequency in the opposite direction that filter B is being adjusted - this was intended to allow the "B" control to act as a sort of "bandpass" adjustement when using the filter in high pass->low pass mode (cascade bandpass), while filter A's control sets the center frequency of the bandpass. In the end, I find it's useful for making all manner of bizzarre noise when cranking it in this mode Laughing

My page about it is here:
http://mypeoplepc.com/members/scottnoanh/birthofasynth/id10.html

Back to the nonlinear function and how useful it is, here's a sample of what turned out to be a longwinded, repetitive Klee piece. It's a single sawtooth going through the high pass section with the resonance cranked up, then through the low pass section to take off the high frequency hash. This is with the fundamental frequency set fairly high - the low portion is the filters non-linear reaction to the signal. The end result is a very thick sound that would have you think it's not just a single sawtooth. It is passing through the Dim C to liven it up, but still, there's a lot of frequency there that wouldn't be there if that high pass wasn't kicking in that wonderful resonance.

The full long-winded thing is here:

http://mypeoplepc.com/members/scottnoanh/sitebuildercontent/sitebuilderfiles/klee_key2.mp3

Like I say, fairly long winded. The Klee is driving the whole thing. The MS-20 filter voice is controlled by a CV output of the Klee and the keyboard. In order for the nonlinearity to track the voice, I patched the keyboard voltage into its V/Oct input, and the Klee voltage into one of the modulation inputs. If that tracking voltage isn't there, the filter's voice will "crack", so to speak, which is a neat effect, but not what I was after here. In the fadeout of the longer piece, you can hear me crank the "A" control while the two filters are controlled in tandem. I had to fade it there, because the D8 was out of room.

The non-linear feedback idea sounds very interesting.

Cheerio,
Scott

Klee_key2_piece.mp3

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Single sawtooth through dual MS 20 (resonant high pass to low pass) with Dim C thrown in.

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