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 Forum index » DIY Hardware and Software
How to convert MFOS 12 db SVF to 15V operation? Fixed!
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Coriolis



Joined: Apr 11, 2005
Posts: 616
Location: Stilling, Denmark

PostPosted: Thu Nov 23, 2006 4:54 am    Post subject:  How to convert MFOS 12 db SVF to 15V operation? Fixed!
Subject description: God I'm dumb! But it doesn't oscillate...?
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This is mentioned in the thread about voltage dividers too:

Has anyone here built Ray's 12 db svf and succesfully converted it to 15V operation? I'm talking about the one without vc res here:

http://www.musicfromouterspace.com/analogsynth/statevariablefilter.html

As far as I can see, it would involve changing the values of a whole bunch of resistors, but exactly which ones, and to what values, is beyond my capabilities to figure out.
I looked at the schem for his other svf to find clues, but they are quite different designs.

Any clues?

C

Last edited by Coriolis on Tue Jan 16, 2007 12:10 pm; edited 1 time in total
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Uncle Krunkus
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PostPosted: Thu Nov 23, 2006 7:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Same answer.

A 7812, a 7912 and 4 caps. Wink

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Coriolis



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Location: Stilling, Denmark

PostPosted: Thu Nov 23, 2006 7:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Jeez, you're everywhere! Shocked

Yeah, but if I use regs every time I come across a 12v ckt, I won't learn how to convert it will I? Wink

C
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Uncle Krunkus
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PostPosted: Thu Nov 23, 2006 7:23 am    Post subject: Reply with quote  Mark this post and the followings unread

There are heaps of other things which I'm alot more interested in learning. Laughing
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Coriolis



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PostPosted: Thu Nov 23, 2006 7:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes...priorities, priorities... thinking

C
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synth_ollie



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PostPosted: Thu Nov 23, 2006 7:50 am    Post subject: Reply with quote  Mark this post and the followings unread

on the mfos startpage you can read :

>Do your circuits work
>with +/-15V?
>All of my circuits will work with +/- 15 volts and in all >probability, with no changes.

I´ve built this vcf and I worked fine on +/- 15v as it is

cheers
OLLIE
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Coriolis



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PostPosted: Thu Nov 23, 2006 8:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Really? That's weird, because on mine, the range is way off... Confused
Strange...

C
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synth_ollie



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PostPosted: Thu Nov 23, 2006 3:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Coriolis wrote:
Really? That's weird, because on mine, the range is way off... Confused
Strange...

C


well it was a while ago since I used it, but as I remember there were no problems... but Im sure you can get the range ok by changing some resistor values
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Coriolis



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Location: Stilling, Denmark

PostPosted: Sun Jan 14, 2007 1:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry to dig up this old thread, but I was just looking at the schems for both of Ray's svf designs and wondered:

On his vc res design, which he sells boards for, the frequency pot sits between + and - 12V, with the wiper carrying the cv.

On the other one (the one I'm building), frequency pot sits between + 12v and ground, with the wiper carrying the cv!

What's going on there? I know I said in the first post of this thread, that they were two "very different" designs, but I take that back: apart from the vc res part, they actually look very much the same, except for this frequency pot business. Could this be why running it on +/-15V screws things up?

C
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Coriolis



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PostPosted: Tue Jan 16, 2007 12:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, it's official - I'm a grade-A moron.
I think I've been over that board a dozen times or so, checking for component values, solder bridges, etc. For some reason though, I didn't think to check the trimmer - how about that, instead of a 100R trimmer, I put in a 100K!

Now it works... Embarassed
Guess there's a lesson in there: To debug a circuit effectively, assume that you have done everything wrong!

Only thing that isn't quite there yet, is that it doesn't self-oscillate at max resonance - which it is supposed to do. Am I right in thinking about reducing the value of R4 (47k at point "Q1" next to the input) to get more feedback?

http://www.musicfromouterspace.com/analogsynth/statevariablefilter.html

C
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Uncle Krunkus
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PostPosted: Tue Jan 16, 2007 3:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Not a moron at all!

To accept that there may be a fault in your beautiful new creation, and then go and find said fault, accept it, and own it, and fix it! Now that's the work of genius!

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synth_ollie



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PostPosted: Tue Jan 16, 2007 3:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

mine did not self oscillate either....
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