MS-20 (LM-13700 version),Polivoks or EMS VCF on veroboard?

[hoyager]

You can get high pass by pulling the grounded end of C4 (1n) up, using that end as the input.

[LektroiD]

[synthesist]

I read somewhere that the original ms20 filter works in a way, that the signal goes through the highpass first before it passes the lowpass filter?

Is it true, or do I remember wrong? If yes, I would like to give this a try.

[remork]

yup, HP first, then into LP.

[synthesist]

Well it is a few months ago now that I build the filter but there is one thing that is bugging me. If I drive 2 soundsources into the VCF I have to be very carefull not to turn on the volumes of the incoming sounds too loud or the VCF just switches off
Same thing happens if I pump too high control voltages into it, but then it only happens if I open the cutoff frequencie knob all the way up.
Pretty annoying because it is hard for me to know when it is too much.

Do you guys think this is "normal" or can I avoid this somehow?

[isak]

Hi Guys.

This looks like a very cool project.
Can anyone tell me what is the range of the filter?
Is it full range 20Hz to 20Khz?

Cheers,
Isak E.

[mrkva]

+1 for the updated version. anyone?

[hoyager]

[robboten]

Anyone have a PCB layout for the Rene MS-20 with 13700?

[oculus]

i just breadborded just by going after the schematic on René Schmitz page.
im finding the resonance way to much with the 1n cap which is located near the led´s(diodes) i tried put 220 pf ceramic and it´s seems to be nicer the resonance knob doesn´t scream as suddenly now.

btw im using 12Volt , resonance knob 100k and cutoff 47k

[isak]

Thanks for the info.
The 1n you reffering to is the one from the left in the schematics?

Cheers,
Isak E.

[oculus]

[isak]

2n you say...mmm...
Where did you saw that?

[oculus]

[isak]

Hi oculus.

i put 2.2nF, it made the reso much stronger and unstable, screems like hell, the peak level is very high/distorted.
tryied with 220pF, the reso was to weak.
actually the 1nF was the best chice but yet again...not perfect.
i didnt do the stripboard version, i did the Jorg Schmitz one.
http://www.analog-synth.de/synths/mod2/ms20filter/rene_ms20_filter_clone%20rev%204.pdf

you can hear sound demos in the next link..
http://electro-music.com/forum/topic-56326.html

i'm not happy with the reso sound yet and hope i'll manage to fix it with the help of the members here.

cheers,
Isak E.

[Sebo]

Hi:
I built mine using the Schmitz PCB too.
The reso sounds OK, but is not exactly like the MS-20 reso, quite right but..
The original design uses 3 diodes in series instead the LEDs to limit the reso. I used green LEDs (colour is important), but I always wanted to try the diodes.
Also I built the One Board Farm monosynth from Motohiko Takeda that uses an MS-20 VCF clone based in the Haible schematic, and it sounds slightly better. The only difference I found is in the voltage divider in the input of the first OTA, and it used a LM13700 instead two CA3080.
Also the filter is very sensitive to input levels, is not adapted to modular levels, so at high input levels (10Vpp from a VCO without attenuation) the reso didn't self oscilate, lowering the level to half (5Vpp seems to correspond to the levels inside the MS-20) the reso works at it should.

[isak]

Thank for replying Sebo.

did you hear my sound demos?
Is it like yours?
I used 2 green LEDs as well.
What kind/type of diode in the original scheme?
actually the HP sounds really good, I love the HP very much.

Another problem I have ( I think it's related to the vco it self) the square don't sound good as the saw, the reso is not that strong, it's sounds like the vco is choking the reso for some reason.
Maybe it's related to what you said about the 10Vpp?
Any way the ody vco is not 10Vpp, it's 5 or 6Vpp with 12V power supply and 7 or 8Vpp with 15V power supply ( if I'm not mistaken).

[Sebo]

The waveforms of the Odyssey VCO have a DC component, they aren't -2.5V to +2.5V, they are 0V to 5V (and 0V to 6V), I suspect that is causing you trouble.
ARP uses DC decoupling caps at the inputs of the VCF, you can do that or make a DC bias compensating circuit. I did a leveler and DC compensating circuit to get -5V to +5V out of the Odyssey VCO but I have to attenuate it to work right with this filter (I have attenuators in all my filters).

[isak]

I will have all ody vco's going through this mixer...
http://yusynth.net/Modular/EN/MIXER/Mixer-2U.html
You think it would help?

[Sebo]

No isn't helping as that mixer is DC capable, so no DC filtering.

[isak]

[Sebo]

Well... using a decoupling cap at the input of the MS-20 VCF is not that easy as I tought, as input impedance is lower than normal (because of the OTA). You can try conecting a 22uF cap in series with the input, I think It should work, but I'm not sure how this will afect the input impedance.

If you want to play safe, is better to decouple the mixer inputs as they are higher impedance, connect a 10uF cap between the wiper of the input pot and the input resistor (in every input you want to decouple).

The caps could be electrolitic but tantalum is better. The + leg of the cap should be connected to the input (where the signal input the circuit).

[isak]

Ok, I'll try that.
If do that won't i turn the mixer to AC mixer?

[Sebo]

Yes, it will be an AC mixer.
You can use a switch to bypass the cap, and choose between AC or DC.

[isak]

Thanks Sebo.

Please explain to me when I will want to use AC mixer and when DC mixer?
I don't quite understand.
Another Q..
my chain is like follow, VCO's--->mixer--->VCF--->VCA.
if my mixer is AC what will be the VCA? AC or DC?