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PCB pattern for René Schmitz "late" MS20 VCF?
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Phazinhead



Joined: Feb 12, 2008
Posts: 4
Location: France

PostPosted: Sat Mar 29, 2008 4:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi everybody !

I have some questions to ask you before buying some parts for this filter :

-What does it make if I change the 100k log potentiometer of resonnance by a 50k pot ?

-what is the voltage range of the CV inputs ? -> could I control the cutoff on the whole audio range with a CV going only from 0 to +15V ?

-what does it make if I only connect the cutoff potentiometer from +15V and ground, instead of +15 and -15V ?

- I can't find 2SA798 transistor or SSM2220, could replace it by BC557C or 2N3906 ? would this change a lot the "MS20 filter sound" ?

thanks a lot for your advice Smile

p.s : the MS20 filter I'm planning to do is this one :http://electro-music.com/forum/phpbb-files/ms20_13700version_142.gif
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bubblechamber



Joined: Nov 04, 2006
Posts: 279
Location: NYC
Audio files: 1

PostPosted: Sat Mar 29, 2008 6:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

as long as you get the pins right you can use the bc557 or 2n3906. I switched 2n3906s for the SSM2210 once I got the filter working. those transistors are for the expo convertor and without a tempco for temp stability I thought the SSM was a bit overkill at $4 each. the better you match your 2n3906s the better it will track the CV, but even with the SSM210 I doubt it's anywhere close to 1V/oct.
so, swapping transistors for the chip will not change the sound, just the way it tracks and responds to CV and I have not really noticed and real change.
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Phazinhead



Joined: Feb 12, 2008
Posts: 4
Location: France

PostPosted: Sun Mar 30, 2008 6:10 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks bubblechamber !

okay, I'll try some bc557 or 2n3906. I've made this PCB : http://www.analog-synth.de/synths/mod2/ms20filter/rene_ms20_filter_clone%20rev%204.pdf , in your opinion, what are the transistor used here ? could I put BC557 without modifying the pins ?

What about of replacing the 100k resonance potentiometer by a 50k ? will I get more or less resonnance ?

A last question about the cutoff CV input : for many reasons the cutoff potentiometer will not be mounted on my MS20 filter, is it possible to control the cutoff frequency from 0 to 20kHz with a voltage going only from 0 to +15V, in using the CV input ?

thanks ! Smile
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bubblechamber



Joined: Nov 04, 2006
Posts: 279
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PostPosted: Mon Mar 31, 2008 8:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Phazinhead wrote:
thanks bubblechamber !

okay, I'll try some bc557 or 2n3906. I've made this PCB : http://www.analog-synth.de/synths/mod2/ms20filter/rene_ms20_filter_clone%20rev%204.pdf , in your opinion, what are the transistor used here ? could I put BC557 without modifying the pins ?

they will both work equally well here, use what ever you have on hand. if you can match them the expo converter will work be a little smoother.

What about of replacing the 100k resonance potentiometer by a 50k ? will I get more or less resonnance ?

I did not notice more or less with a 50K pot, but I had better control with the 100K.

A last question about the cutoff CV input : for many reasons the cutoff potentiometer will not be mounted on my MS20 filter, is it possible to control the cutoff frequency from 0 to 20kHz with a voltage going only from 0 to +15V, in using the CV input ?

that should work just fine, but I would test it out to make sure. as long as there is a 100K resistor in the CV path it should be fine, that's all the pot is doing anyway. but follow the schematic when you set the CV up, I used 47K resistors between the power rail and the pot, this gave me more range, with the pot hooked directly to the rails the filter was silent for the first third and unchanged for the last third of the pots range.

thanks ! Smile


no problem.
d
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Phazinhead



Joined: Feb 12, 2008
Posts: 4
Location: France

PostPosted: Tue Apr 01, 2008 4:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Great ! thanks Bubblechamber Very Happy

I'll try this and tell you what it gives, in 2 weeks, time to buy all the stuff to do it Surprised
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bubblechamber



Joined: Nov 04, 2006
Posts: 279
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PostPosted: Tue Apr 01, 2008 2:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

let me know if you run into any problems in the build. good luck, I'm looking forward to seeing what you come up with.
d
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widdly



Joined: Jun 25, 2007
Posts: 268
Location: singapore
G2 patch files: 2

PostPosted: Tue Apr 01, 2008 6:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

I built this last night and have some problems. I built mine using the CA3080's as per Rene's original schematic. However I added the attenuator on the input, changed the input resistor, added the resistor on before the resonance pot and swapped the capacitor for an electrolytic on the output.

It filters fine but I don't get much in the way of resonance. I cannot really hear much difference at all sweeping the res and it certainly doesn't oscillate. I've tried attenuating the input but with no luck.

I traced it with an audio probe and I there is audio in the resonance path right up to the capacitor where it is mixed back with the input. I only had a ceramic capacitor for this part. Would that make a difference?

Last edited by widdly on Thu Aug 05, 2010 10:17 pm; edited 1 time in total
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bubblechamber



Joined: Nov 04, 2006
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PostPosted: Wed Apr 02, 2008 12:57 am    Post subject: Reply with quote  Mark this post and the followings unread

the resistor before the resonance pot might be the problem. I have built mine with 10uF electrolytic and they are very rezy. i also used a pot on the input and used a 10K like Rene's schematic, not a 47K as in the OTA version. I would try removing the resistor before the resonance pot first and replacing the cap.
d
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widdly



Joined: Jun 25, 2007
Posts: 268
Location: singapore
G2 patch files: 2

PostPosted: Wed Apr 02, 2008 1:52 am    Post subject: Reply with quote  Mark this post and the followings unread

For the 10uF, which cap are you talking about? I've tried a 0.47uF ceramic and a 10uF electrolytic at the output. I couldn't hear any difference.

Or did you mean to replace the 1n cap with a 10uF feeding between the OTA and the opamp? I'm using a 1n ceramic here.

I have tried without the 47k on the input and it was much the same.

I'm thinking I must have a mistake somewhere else. I think maybe I've bodged the opamp in the feedback path. AFAIC it should be giving 5x gain.

Last edited by widdly on Thu Aug 05, 2010 10:16 pm; edited 1 time in total
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bubblechamber



Joined: Nov 04, 2006
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PostPosted: Wed Apr 02, 2008 11:30 am    Post subject: Reply with quote  Mark this post and the followings unread

the 10uF should be on the output. If I get a chance today I'll try and replace my 10uF with a .47 and see if there is a change.
I had some trouble with Rene's schematic myself and I had much better luck with this one
http://electro-music.com/forum/phpbb-files/ms20_13700version_142.gif
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bubblechamber



Joined: Nov 04, 2006
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PostPosted: Wed Apr 02, 2008 6:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

well, a .47uF ceramic really killed of the Resonance on mine, but a 100uF was no different than a 10uF. With the .47uF there was almost no Resonance until it hit the self oscillation point. It sounds like there is a problem elsewhere in your filter. I wish I could be more help...
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abelovesfun



Joined: Dec 17, 2012
Posts: 40
Location: Portland, OR

PostPosted: Mon Oct 31, 2016 6:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Here is my update of the Ms.20 with HP and LP.
http://aisynthesis.com/wp-content/uploads/2016/10/MS20.pdf

Close to ready for production, I have the following to troubleshoot:

1. Re-introduce a 10k input resistor to the input, and a 220r to ground, as in the Rene circuit to see if it helps with clipping. Currently, at overly hot levels, the filter distorts and acts irregular.

2. Should C10 be elctrolytic with the + facing "output?" Currently the filter "thumps" out when switching between hp and lp sometimes, requiring the cutoff to change before it kicks back in. Update: Tried this, but when resonance is high, the filter will still go quiet when switching between modes.

3. Confirmation of orientation of the two BC558s - I think this is not quite right... Might try it with BC559s in a different configuration.

_________________
Experimental and modular music at: https://soundcloud.com/she-suburban-heroin-electronics

I make Eurorack DIY Kits (pcb and or panels also available): aisynthesis.com
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fonik



Joined: Jun 07, 2006
Posts: 3950
Location: Germany
Audio files: 23

PostPosted: Tue Nov 01, 2016 12:54 am    Post subject: Reply with quote  Mark this post and the followings unread

abelovesfun wrote:
1. Re-introduce a 10k input resistor to the input, and a 220r to ground, as in the Rene circuit to see if it helps with clipping. Currently, at overly hot levels, the filter distorts and acts irregular.

the 10k + 220R to GND form a voltage divider which is needed to get signal down for the OTA. The LM31700 datasheet tells you how much the OTA can handle.
I would leave the 220R on the OTAs input at any time (even for HP). I would also add the 10k (or even 100k right after the attenuating pot for both the LP and the HP input.

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matthias
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fonik



Joined: Jun 07, 2006
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PostPosted: Tue Nov 01, 2016 12:57 am    Post subject: Reply with quote  Mark this post and the followings unread

abelovesfun wrote:
Here is my update of the Ms.20 with HP and LP.
http://aisynthesis.com/wp-content/uploads/2016/10/MS20.pdf

You use GND and PGND in your schematic. What is the actual difference?

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cheers,
matthias
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abelovesfun



Joined: Dec 17, 2012
Posts: 40
Location: Portland, OR

PostPosted: Tue Nov 01, 2016 8:43 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:

You use GND and PGND in your schematic. What is the actual difference?


It is a split board, that connects via two 6 pin headers. It's for euro and I wanted all panel mount connectors, and for it to be shallow, so I used two pcbs, one for the front panel PCB (PGND) and one for the circuit/power PCB (GND). They connect via a 6 pin header.

I'll add those input resistors.
I tried it with BC559s yesterday and there was no real difference there...

Still the same issues. I also noticed that the HP has a lot of "distortion" when the resonance is high. If anyone is dedicated to troubleshooting and in the US, I'd be happy to send out a PCB+parts+panel.

_________________
Experimental and modular music at: https://soundcloud.com/she-suburban-heroin-electronics

I make Eurorack DIY Kits (pcb and or panels also available): aisynthesis.com
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mikemoretti



Joined: Apr 29, 2014
Posts: 5
Location: Boston, USA

PostPosted: Wed Jan 11, 2017 8:18 pm    Post subject: VCF resonance voltage is high Reply with quote  Mark this post and the followings unread

I breadboarded this VCF and whenever you turn up the resonance, the voltage doesn't stick to the +/-5v range but goes to -5 to +10v. When I power it via +/-12v it goes between +/-8v with resonance turned up. Any ideas why this would happen or how to fix it?

Thanks!
-m
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Cfish



Joined: Feb 24, 2016
Posts: 477
Location: Indiana

PostPosted: Fri Jan 13, 2017 4:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

It really just sounds like a little mistake on the bteadboard. I looked time and time again and then find it.
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mikemoretti



Joined: Apr 29, 2014
Posts: 5
Location: Boston, USA

PostPosted: Sat Jan 14, 2017 3:21 pm    Post subject: It was the LEDs Reply with quote  Mark this post and the followings unread

I hadn't added the leds. I didn't think they mattered, but I guess the ~3v voltage drop across them is actually important.

Thanks!
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