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 Forum index » DIY Hardware and Software
Kobol Waveshaper
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fokale



Joined: May 06, 2010
Posts: 5
Location: Istanbul

PostPosted: Thu May 06, 2010 3:34 pm    Post subject: Kobol Waveshaper Reply with quote  Mark this post and the followings unread

Hi forum, did anybody try to build or breadboard the Kobol waveshaper circuit on Mark Verbos' website? I tried to simulate the circuitry on Electronics Workbench without success. I am suspicious about the component values.

Also a brief description of the circuit will be highly appreciated.

Thanks in advance.
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andrewF



Joined: Dec 29, 2006
Posts: 1174
Location: australia
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PostPosted: Thu May 06, 2010 5:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi
haven't tried the kobol
but what didn't work in your simulation?
Also does E-bench have 3080 OTAs?
I doubt you could replace them directly with op-amps, would need to modify the circuit a bit.

Very Happy welcome to e-m Very Happy
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fokale



Joined: May 06, 2010
Posts: 5
Location: Istanbul

PostPosted: Thu May 06, 2010 6:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, the software has all the components, I also tested the kobol vco core and got a nice 10V p-p sawtooth wave with about 1 Volt offset. I don't know what's wrong with the simulation, I double checked my circuit against Verbos' circuit and didn't find any errors. Fed with a sawtooth with the same specifications, the circuit outputs a sine-like waveform, but the shape CV doesn't affect the output waveform shape at all. With my poor knowledge of electronics, fiddling with component values doesn't make sense, without understanding how the shaper works. Also interesting to hear that it could work with OPAMPs instead of OTAs.

Thanks for the response and the welcome Smile
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yusynth



Joined: Nov 24, 2005
Posts: 1221
Location: France

PostPosted: Fri May 07, 2010 12:27 am    Post subject: Reply with quote  Mark this post and the followings unread

fokale wrote:
Also interesting to hear that it could work with OPAMPs instead of OTAs.


You missunderstood, it was said exactly the opposite.

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Yves
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TekniK



Joined: Aug 10, 2008
Posts: 1062

PostPosted: Fri May 07, 2010 12:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Its the best waveshaper ever,very good sounding.

Awesome results when u modulate it in audio.

I wish u all the best to get it working like the original.
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Dave Kendall



Joined: May 26, 2007
Posts: 413
Location: England
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PostPosted: Fri May 07, 2010 3:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi.

Quote:
Also interesting to hear that it could work with OPAMPs instead of OTAs.


I believe the note on the schemo refers to the final output stage, which is a 3080 wired as a VCA. If I read it right, Mark V suggests this stage could be replaced with an op amp, giving manual rather than VC control of output level.

There is a problem with the circuit as drawn, in that it is not clear where connections crossing are joined or not. The conventional symbol (a dot) is missing in all but 2 cases. For example, at a guess, the traces from the outputs of the two LM324 outputs on the top left *don't* connect to the inputs of the centre two TL082s, but go via a 56K and a 68K resistor and then to pin 5 of the two 3080s on the right top ( *not* the final rightmost one)

The only other things I can guess from looking at it, is that the lower pair of TL082/3080 is involved with square to pulse shaping, and that the top pair is the triangle to saw section. The column of five 324 stages on the left look like they are concerned with processing the CV from the leftmost
324 (an inverting summing amp), and their ouputs connect to the two pairs of 082/3080 waveshapers. They are I believe, all but one, wired as inverting amplifiers with offset/bias inputs or connections, so those should be easy enough to wire up.

I can't guess whether the output of the bottom 3080 is joined to the output of the 324 second from bottom, or whether it goes straight to the 324's input. This 324 might be a comparator?.

Finally, the TL082 is powered from ±18/-14.5. I should imagine that some component values around this area would need tweaking if running from ±15V. If we're unlucky, then the resistor values for the column of 324s on the left will need tweaks too.

These are guesses based on a quick look...... The blue circles are where I *think* the traces are *NOT* joined.

Maybe someone more experienced than me can help out here..... Smile
Hope this helps a bit...Good luck with it!

cheers.
Dave


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yusynth



Joined: Nov 24, 2005
Posts: 1221
Location: France

PostPosted: Fri May 07, 2010 3:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
These are guesses based on a quick look...... The blue circles are where I *think* the traces are *NOT* joined.


You are right.

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Yves
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frijitz



Joined: May 04, 2007
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Location: NM USA
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PostPosted: Fri May 07, 2010 9:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Dave Kendall wrote:
There is a problem with the circuit as drawn, in that it is not clear where connections crossing are joined or not. The conventional symbol (a dot) is missing in all but 2 cases.

The way I see it, the only error is that a dot is missing at one point (by the PW input). Without a dot the wires cross, with one they connect.

Has anyone built this design? Where would you get the +18V in a normal system?

Very Happy

Ian
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Dave Kendall



Joined: May 26, 2007
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PostPosted: Fri May 07, 2010 10:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Ian.

OK - is it generally assumed (or perhaps is the convention) that only when there are 2 wires actually crossing that a dot needs to be marked to show a connection there?

There are many places where 3 wires are shown at a node - is it assumed that they *always* connect (without a dot?)

That would make sense, but I guess could be confusing for newbies....
(like I still am really Wink )

cheers,
Dave
(old newbie)

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frijitz



Joined: May 04, 2007
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PostPosted: Fri May 07, 2010 12:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Dave Kendall wrote:
OK - is it generally assumed (or perhaps is the convention) that only when there are 2 wires actually crossing that a dot needs to be marked to show a connection there?

Let's just say it's a common way of drawing schematics, but not by any means the only way. Generally you have to just figure out what convention the drawing is using more or less by common sense. Of all the mistakes you see on schematics, this is by far the most common type -- being inconsistent with how crossings are treated.

Nowadays I show unconnected crossings with little gaps on one of the lines and connected crossings with a dot. But I try not to have connected crosses -- it's just about as easy to use T's for all connections.

Quote:
There are many places where 3 wires are shown at a node - is it assumed that they *always* connect (without a dot?)

Yes. Otherwise one of the wires would be going nowhere!

Very Happy

Ian
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Dave Kendall



Joined: May 26, 2007
Posts: 413
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PostPosted: Fri May 07, 2010 12:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the explanation Ian.

I guess I got it my head that there should always be dots at junctions, so was sort of looking at it backwards.
No more beer for me today......

Quote:
Yes. Otherwise one of the wires would be going nowhere!


Ahem, well, er, yes.... Embarassed

Smile

cheers,
Dave

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fokale



Joined: May 06, 2010
Posts: 5
Location: Istanbul

PostPosted: Fri May 07, 2010 6:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks guys for the brainstorming, but after a bit of goggling, I found out that the CA3080 model in the software's library is incorrect. So the only option left for me is to breadboard the circuit and see. I also need a power supply with the extra 18V tap. By the way, what is the purpose of that asymmetrical powering of TL082?
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v-un-v
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Janitor


Joined: May 16, 2005
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PostPosted: Sat May 08, 2010 12:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Fokale! Nice to hear from you in Istanbul!

I loved Istanbul! A great city. I visited Istanbul a few times, when my wife played there.

welcome to electro-music.com! Very Happy

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fokale



Joined: May 06, 2010
Posts: 5
Location: Istanbul

PostPosted: Sat May 08, 2010 7:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah it's a nice city to live in, if not the best. Especially in springtime. Come again and PM me if you do!! Smile
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forbin



Joined: Jan 29, 2009
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Location: Fremantle, Australia

PostPosted: Mon May 10, 2010 10:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Checking the circuit against the original schematic that I found with a bit of Googleing (see: http://www.matrixsynth.com/blog/media/rsf/rsfkobolschematics/) and I think I can see Mark Verbos's problems!

I tried doing an LTSpice simulation -- the OTA models that they have on the yahoogorup site aren't too bad. Anyway I would say that there are certainly a couple of mistakes. The 220k on the +ve input to the lower OTA, being fed by the PWM modulation, should be 220 ohms. Look at all the other OTA's and you can see that -- the input range of the 3080 is pretty low so that usually the potential divider feeding it has a largish resistor followed by a pretty small one...

The other resistor that seems rather odd is the feedback resistor on the wave-shape buffer. Currently 220 ohms. The parts list does seem to suggest that it is 220 (if you can believe that the smudge is R204 -- the top one could be anything!)

Anyway looking at trying to use two LM13700's instead, keeping the basic topology and see what happens...
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fokale



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PostPosted: Tue May 11, 2010 2:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Looking forward to your results!
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oberkorn



Joined: Nov 05, 2009
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PostPosted: Wed Jan 01, 2014 7:26 am    Post subject: Reply with quote  Mark this post and the followings unread

did anyone get this to work (last update was 3.5 years ago)?
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