MS20 Inspired VCO WIP

[brother303]

Hi,

[Pantheon]

A sync feature was something that I realy wanted to include from the outset of this project. There were a few problems with the old design that I wanted to get rid of. My old method wasnt a true reset of the waveform, it actualy just pushed the falling ramp back up by a certain amount. It sounded great, but would change the frequency of the core for some reason.

I just found a much more stable way to achive a good hard sync, by injecting a pulse into the tail of D1. It looks good in my spice model, so i'll try and include it in my next board. A 5v pulse will completely restart the saw tooth.
I'm going to try and design a good pulse generator for this soon.

Pic of this new method is attached:


[edit]
Damnit, even that method creates some instability. So im trying yet another method, by injecting a negative pulse into the base of pnp T1.
Perhaps that will be more stable.
[/edit]

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[ericcoleridge]

This project of yours is making me want to have other sections of the MS20 available as PCBs.

I already have both VCFs assembled and tested; they sound amazing. The PCBs I made are for the later discrete daughter board version of the MS20 LPF+HPF, which was the one I had on my MS20. The layouts are on line.

But now I think I'll try laying out the VCA, LFO, and HADSR in Layout Express. I've done a few layouts before-- unfortunately, I've yet to make one the works! But I'll give another it try. I've found nice re-draws of the VCA and LFO on Marjan Juekers site, and the HADSR on Juergen Haible's site.

[brother303]

Hi,

[Pantheon]

Perhaps eventually we could group them all together in one package for a Mutant MS20 Clone. That would be pretty awesome actually.

I'd defiantly be interested in the VCA clone as I'll have to make one to match these VCO's soon. Something with a bit of character would be great. Any chance you could post a link to these redrawn schematics?

PS: the new sync appears to behave nicely this time, and sounds really great in the simulation. I'm going to mod my 1st prototype soon to try it out in the real thing.

[brother303]

Hi,

[brother303]

Hi Pantheon,

I did a quick search...

http://electro-music.com/forum/topic-33190.html

Maybe helpful.

[ericcoleridge]

MS20 VCA:
http://urekarm.tripod.com/synth/jx_vca.pdf

MS20 LFO:
http://urekarm.tripod.com/synth/ms20lfo.pdf

MS20 HADSR:
http://www.jhaible.de/jh_vc_hadsr.pdf

MS20 LPF/ HPF, pattern+parts overlay:
http://www.analog-synth.de/synths/mod2/ms20filter/rene_ms20_filter_clone%20rev%204.pdf

[brother303]

Cool,

thank you.

Best regards
Greg

[ericcoleridge]

I made a layout for the VCA using Marjan's drawing; I'll post it here if anyone wants to test it. Ill probably layout the LFO also, but I think the HADSR might be a little beyond my abilities.

[brother303]

Hi,

[brother303]

Hi Pantheon,

I found an old thread here on the board about syncing MS20-vcos.

http://www.electro-music.com/forum/post-104001.html

Cheers
Greg

[Pantheon]

[ericcoleridge]

This is probably not the best place to post these, but, being that they are related, I'll go ahead for now.

These are layouts for the MS20 VCA and LFO, both untested as of 3/21/11. I was pretty careful laying out the VCA, less so with the LFO; But both are very simple and if anythings wrong, shouldn't take much to get them working. The VCA calls for matched BC549s, but I don't know how critical this is.

I used a freeware program called DIY Layout Creator, which is a little buggy. The layouts will need to be re-sized before printing to PnP, and I think they may also need to be reversed.

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MS20 LFO Draft 1.gif
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[brother303]

Hi,

[brother303]

Hi,

@Pantheon: How many ins and outs does your vco provide? Exactly like the "real thing"?

Outs : Tri, saw, square
Ins : V/oct., pwm, freq.1, freq.2

And another question : Is there a coarse and a fine tune pot or an octave switch and a tune pot?

Thanks!

Cheers
Greg

[Pantheon]

It has 5 inputs:

2x - 1/voct inputs
1x - sync input
1x - linear cv
1x - pwm input

1 of the 1/voct should come out to the faceplate, or be routed internaly to a MidiCV converter, etc.

The other one is for the Fine/Course tuning pot. I havent decided exactly how im going to use this yet. Currently im hovering over the idea of octave/finetune. I'll include a diagram of how I wire it, but people should be able to use this to suit themselves I think.

The sync input can connect to the square/pulse wave of any oscillator (at +5v/-5v), and will sync on the rising edge of that wave.

The linear cv is of no use to me but it seems to be a standard thing to include in VCO's so I put one in. Also Sebo might be able to use it to get this oscillator to track from a v/Hertz cv.

The PWM input takes a CV of [0v - 5v] and sets a [50% - 0%] duty cycle, respectively. The PWM cv could also range to -5v to get >50% duty cycle.
I am going to wire a pot as an attenuator feeding into this, and depending on if a jack is plugged into the CV input or not, it will either set PWM directly or attenuate a signal coming in threw the jack.

I has 5 outputs:

1x - Saw wave
1x - Triangle wave
3x - Pulse wave

There are three pulse outputs, so that one can be internaly routed to a second oscillator to allow syncing. One can also be internally routed to a CMOS ring modulator.

Does that seem reasonable?
These features suit me, but feel free to make suggestions, I can still change the board.

Also I have finished routing the new board, so after a double check, i'll etch and test it

[brother303]

Hi,

[brother303]

Hi again,

this is a very interesting link,maybe one or the other already knows it.

http://www.birthofasynth.com/Scott_Stites/Pages/dualms20_main.html

Cool version of the vcf, 2x Rene Schmitz pcbs required.

Combined with two vcas ( http://urekarm.tripod.com/synth/jx_vca.pdf ) nice stereo effects can be achieved.

Best regards
Greg

[Pantheon]

Hey 303,

Thoes are some great links you have there. I have been testing the VCA myself in spice and it seems to function fairly nicely. I made a few tweaks to it that I will share if anyone is interested.

As for the Octave/Finetune switch, im in two minds about what to do with it.
As with the link you provided, I need to use a dual opamp for a buffer, these buffers then feed into the 1v/oct inputs. But I cant decide where to place this little circuit. I would be most happy i think, putting it on a little board of its own. This way, everything is as flexible as it can be, people can pick and choose what they want. The only problem is its a little bit more of a pain to etch/wire everything up, but not much.

If I do choose this route, i'll probably make it pot-mounted so that its less of a hassle. Then you can wire it to both the rotory switch, and the vco board.

So my plan for this mini board is:

4x Inputs:
+12v, -12v, gnd, +5v
these all come from the vco board.

1x Mounted Pot:
this is as a fine tune control, and typicaly covers an entire octave in a full sweep, left to right.

1x Non Mounted Rotary Switch:
This can have up to five steps, each of which represents one octave.

1x Output:
This is the sum of both the pot and the rotary switch, and wires directly into the 1v/oct input on the vco board.

Does that seem like a good plan? I have tested that circuit, and im sure it will work.

I have also made a layout for a small board with the ring modulator on it.

[brother303]

Hi,

[Pantheon]

I have attached the version of the ms20 vca that I simulated. There are a couple of notes on there, for setting line level and synth level outputs. I also added a gain trim pot, as the verson you linked to seemed to output a slightly lower signal level. Also I removed the bias trim, as I couldnt see much reason for it in the circuit. Does anyone know why it was included?

As for the question of puting the ring mod on the vco board, as it stands the vco is realy nicely layed out and everything fits great. If I were to put it on the board, it would either become a very long board, or become a routing nightmare. I quite like the fact that its a very small vco board right now (4.30"x1.50"). The ring mod board is (2"x1") on its own. The ring mod, could have 3 sockets mounted on it, and just attach directly to the face plate, no problem. You could then also use it with other modules.

Im about to finaly sit down and check the vco to make sure its routed correctly. I got a little sidetracked with some tube circuits

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[brother303]

Hi,

[brother303]

Hi Pantheon,

R12 on your vca-schematics is really 1000K?!?

Not 10K???

Cheers
Greg

[Pantheon]