The new 2164 Korgasmatron Dual VCF

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Dr. Sketch-n-Etch
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The new 2164 Korgasmatron Dual VCF

Post by Dr. Sketch-n-Etch » Mon Aug 30, 2010 1:38 am

I wanted to show off my new MS-20 filter clone. Like the MOTM 420, the Frostwave Resonator, and several others, this filter is based on the later version of the MS-20 filter. However, unlike all the other clones, this one is not a direct (or indirect) copy of the LM13600 OTAs-and-buffers topology of the original. Instead, it is based on the SSM2164 quad VCA chip, and realizes the same transfer function with a VCAs-and-integrators topology. The exponential CV response of the 2164 VCAs obviates the need for exponential converter circuitry. Also, unlike the LM13600-based designs, this filter does not add dc offsets to the signal, and therefore does not require AC coupling capacitors in the signal path.

I've also added a new feature: adjustable limiting voltages in the resonance feedback loops. One problem with the original design (and the clones, I think) is that the resonance amplitude is limited to only 1.8V, and as a result the input signal attenuator has to be set pretty low in order to hear any resonance at all in lowpass mode. My new amplitude control eliminates this problem, and now robust resonance can be obtained without sacrificing signal strength.

Finally, the PCB contains two complete MS-20 style filter circuits, each with all the same features of other popular clones, but with a few additional features as well, including both unipolar and bipolar CV controls, separate three-channel mixer output with optional level control, and optional fine tuning.

A picture of my 4U prototype panel is shown below. This is just one of many panel possibilities, and even this one is missing some of the features available on the PCB for lack of space.

I've also attached some sound clips for your listening pleasure. I'm not much of a production engineer, and all I've got is a little Behringer mixer with no effects and an obsolete version of Cakewalk, so apologies in advance for the crappy sound quality. The last one is my shameless attempt to reproduce the second soundclip on the MOTM 420 webpage with a single filter (the one on the right, if you're curious). This was recorded as a .wav but converted later to an .mp3, so the sound isn't so good, but hopefully the character of the filter still comes through. The other three make use of a triple LFO and my recently redesigned version of Ken Stone's CGS analog shift register, and show some of the formant effects one can achieve with the two Korgasmatron filters in series. However, these only scratch the surface of what this beasty is capable of.

Let me know if you're interested in a handmade PCB.
Image
Attachments
Shameless ripoff of the "2 different riffs" clip on the MOTM 420 site, based on a single Korgasmatron filter and my less-than-stellar keyboard skills. Did I come close?
Fake 420 sample.mp3
(678.38 KiB) Downloaded 195 times
After getting this pattern happening with the LFOs and the ASR, I played around with the cutoff and FM 2 controls of both filters.
Fripp Chorus.mp3
(1.96 MiB) Downloaded 249 times
Arkansas, Arkansas, I just love ol' Arkansas!
Gomer Waltz.mp3
(247.39 KiB) Downloaded 190 times
Hey! What's the big idea? Why, I oughta...!
Moe and Curly.mp3
(289.43 KiB) Downloaded 291 times

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fonik
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Re: The new 2164 Korgasmatron Dual VCF

Post by fonik » Mon Aug 30, 2010 2:19 am

Dr. Sketch-n-Etch wrote:I wanted to show off my new MS-20 filter clone. Like the MOTM 420, the Frostwave Resonator, and several others, this filter is based on the later version of the MS-20 filter. However, unlike all the other clones, this one is not a direct (or indirect) copy of the LM13600 OTAs-and-buffers topology of the original. Instead, it is based on the SSM2164 quad VCA chip, and realizes the same transfer function with a VCAs-and-integrators topology. The exponential CV response of the 2164 VCAs obviates the need for exponential converter circuitry. Also, unlike the LM13600-based designs, this filter does not add dc offsets to the signal, and therefore does not require AC coupling capacitors in the signal path.
impressing.
I've also added a new feature: adjustable limiting voltages in the resonance feedback loops. One problem with the original design (and the clones, I think) is that the resonance amplitude is limited to only 1.8V, and as a result the input signal attenuator has to be set pretty low in order to hear any resonance at all in lowpass mode. My new amplitude control eliminates this problem, and now robust resonance can be obtained without sacrificing signal strength.
brilliant
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Moog$FooL$
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Post by Moog$FooL$ » Mon Aug 30, 2010 2:32 am

hup hup!!!

another good one Doc., keep 'em comin'!!

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Post by numan7 » Mon Aug 30, 2010 2:59 am

:tu: right-on doctor e&s - vcf perfection!!! :woah: hmmmm.... let's see now... maybe i could build just a *small* :hihi: 5u format system... diy... hmmmm.... dang! tempting.... tempting... :hmm:

anyways, if there were a nobel synthesis prize, this brilliant design would certainly deserve to be on the list!!! :yay::yay::yay:

kudos,
n7
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Post by ndkent » Mon Aug 30, 2010 4:38 am

Good work!

Just wanted to mention that adding "tron" to the name at this point makes one, well me at least, assume you were using hacked Monotrons,

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Post by Synthbuilder » Mon Aug 30, 2010 4:50 am

ndkent wrote:Just wanted to mention that adding "tron" to the name at this point makes one, well me at least, assume you were using hacked Monotrons,
While I thought of the young Jane Fonda... although it was Klute that did it for me.

Tony

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Post by Moog$FooL$ » Mon Aug 30, 2010 4:58 am

Synthbuilder wrote:
ndkent wrote:Just wanted to mention that adding "tron" to the name at this point makes one, well me at least, assume you were using hacked Monotrons,
While I thought of the young Jane Fonda... although it was Klute that did it for me.

Tony


:lolspew:

well at least you're not thinking of an old Jane Fonda....... just wish i knew who or what Klute is??? :hmm: what was the name of that film??

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Dr. Sketch-n-Etch
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Post by Dr. Sketch-n-Etch » Mon Aug 30, 2010 12:10 pm

Moog$FooL$ wrote:well at least you're not thinking of an old Jane Fonda....... just wish i knew who or what Klute is??? :hmm: what was the name of that film??
...uh, Klute?

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Post by Dr. Sketch-n-Etch » Mon Aug 30, 2010 12:17 pm

Synthbuilder wrote:
ndkent wrote:Just wanted to mention that adding "tron" to the name at this point makes one, well me at least, assume you were using hacked Monotrons,
While I thought of the young Jane Fonda... although it was Klute that did it for me.
Well, Tony, you're close. However, I was thinking more Diane Keaton.
Image

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Post by nerdware » Mon Aug 30, 2010 1:23 pm

A very tasty clone! I love the demos too. Thanks. For anyone wondering about that film ref... Klute on IMDB.
https://vimeo.com/user2264453
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Post by russma » Mon Aug 30, 2010 7:09 pm

...or the good doctor's reference to the "Orgasmatron" from "Woody Allen's film "Sleeper."

:tu:

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Post by keykeyeyekit » Mon Aug 30, 2010 8:12 pm

This filter drips with awesome.

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Moog$FooL$
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Post by Moog$FooL$ » Mon Aug 30, 2010 9:21 pm

saw a post on Matrix about this very module.

go Doc. go!!

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Post by transfixer » Tue Aug 31, 2010 2:36 am

:woah: :woah: :woah: :party: :party: :party:

great sound, nice name!
could it be shrinked into euro format?

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Post by Synthbuilder » Tue Aug 31, 2010 2:54 am

Dr. Sketch-n-Etch wrote: However, I was thinking more Diane Keaton.
Ah... that orgasmatron from Sleeper. I remembered it's usage in the earlier and cheesy film Babarella (that's the Jane Fonda reference) It's the machine that the evil Duran Duran uses on her to 'torture' her. But I see from Wiki it isn't referred to as the orgasmatron but the 'excessive machine'.

And Klute? Ruddy excellent film. Haven't seen it for years though... so it may have aged somewhat.

Tony

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Post by Dr. Sketch-n-Etch » Tue Aug 31, 2010 2:56 am

transfixer wrote:great sound, nice name!
Thanks, and thanks!
transfixer wrote:could it be shrinked into euro format?
I think so. I'm still waiting to hear what the maximum allowable PCB dimensions are for Euro format. My current board is 2.1" x 6.6" which is a little bit long for Euro, I think. I can probably make it about 4" x 4" with some changes to the layout. If it comes to that, I may bite the bullet and get proper boards made professionally. I'm hesitant to do board-mounted pots, because that really locks you into a certain format, and also because only a small fraction of the total pots could be accomodated on the board, so really what's the point?

If you would like to volunteer to tell me what the board size limits are for Euro, I'll think about shrinking my board to fit.

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Post by Dr. Sketch-n-Etch » Tue Aug 31, 2010 3:04 am

This is the board, by the way. As you can see, things are pretty tight. The two filter circuits are essentially mirror images of each other on opposite sides of the "chip axis". However, I think I could break the circuit at a couple of spots and make the board wider and shorter.

Image

Image

Image

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Post by Junk Rhythm » Tue Aug 31, 2010 3:27 am

Dr. Sketch-n-Etch wrote: I think so. I'm still waiting to hear what the maximum allowable PCB dimensions are for Euro format. My current board is 2.1" x 6.6" which is a little bit long for Euro, I think. I can probably make it about 4" x 4" with some changes to the layout. If it comes to that, I may bite the bullet and get proper boards made professionally. I'm hesitant to do board-mounted pots, because that really locks you into a certain format, and also because only a small fraction of the total pots could be accomodated on the board, so really what's the point?

If you would like to volunteer to tell me what the board size limits are for Euro, I'll think about shrinking my board to fit.
On my cases (Elby Subracks) the space between mounting rails is 112.5mm. I would shave off 4mm to allow for a little extra space bringing us to 108.5mm. This would provide a bit more ease in moving modules in and out of the system.

Doepfer's A100P6 cases have a useable depth of 80mm from the front panel to the PSU in the rear of the case. In the sections that do not contain the PSU, the depth is 100mm from the front panel to the rear of the case.

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Post by Dr. Sketch-n-Etch » Tue Aug 31, 2010 3:34 am

Junk Rhythm wrote:On my cases (Elby Subracks) the space between mounting rails is 112.5mm. I would shave off 4mm to allow for a little extra space bringing us to 108.5mm. This would provide a bit more ease in moving modules in and out of the system.

Doepfer's A100P6 cases have a useable depth of 80mm from the front panel to the PSU in the rear of the case. In the sections that do not contain the PSU, the depth is 100mm from the front panel to the rear of the case.
Who came up with this midget format, anyway? :mad:
It looks like I'll have to get this board down to about 4" x 5". That's doable, but not for a couple of weeks, when things at work settle down a little bit.

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Post by emdot_ambient » Tue Aug 31, 2010 10:07 am

Dr. Sketch-n-Etch wrote:Who came up with this midget format, anyway? :mad:
:hihi: Europeans apparently.

Awesome module, BTW!

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Post by Dr. Sketch-n-Etch » Tue Aug 31, 2010 1:12 pm

emdot_ambient wrote:
Dr. Sketch-n-Etch wrote:Who came up with this midget format, anyway? :mad:
:hihi: Europeans apparently.

Awesome module, BTW!
Touche! (and thanks!)

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Post by emdot_ambient » Tue Aug 31, 2010 2:13 pm

Dr. Sketch-n-Etch wrote:...I may bite the bullet and get proper boards made professionally...
As in, available for others to purchase? 'Cause I'd definitely go for one.

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Post by Dr. Sketch-n-Etch » Tue Aug 31, 2010 4:14 pm

emdot_ambient wrote:
Dr. Sketch-n-Etch wrote:...I may bite the bullet and get proper boards made professionally...
As in, available for others to purchase? 'Cause I'd definitely go for one.
Actually, you can buy one now, but it'll be one of my handmade ones. In fact, I sold two just lastnight. I'm (stupidly) charging only $20 (US) + $5 (US) shipping. It'll be one-sided, 2" x 6.6", with tinned traces, but NO silkscreening or through-hole plating -- exactly the same as the board in the pictures below. I'll also send the jumper kit so you don't have to mess with cutting the jumpers to size, and enough documentation to get you through it (it's actually a fairly straightforward build).
Send me a private message if you want to buy a board, cause I'm takin' orders now!

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Post by Dr. Sketch-n-Etch » Fri Sep 03, 2010 2:08 am

In addition to handmade boards, I thought it would also be nice to offer handmade panels like the one in the picture. This would be in MOTM format, 4U wide, with black graphics baked on bare aluminum with Lazertran. They're very nice looking, and extremely durable.

If you're interested, send me a p.m.

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Post by fiveman » Fri Sep 03, 2010 11:13 am

For those of us who make boards, are you going to put up a clean template for us to copy and iron on. The photos you posted give a useable image but less experienced etchers may have trouble making up good boards.

Nice layout. A pro version would be a great value and an easy build

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