electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Articles  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links  |  Store
Forum with support of Syndicator RSS
 FAQFAQ   CalendarCalendar   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   LinksLinks
 RegisterRegister   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in  Chat RoomChat Room 
Live streaming at radio.electro-music.com

  host / artist show at your time
<on air> EdisonRex Edison's Electronic Review
Please visit the chat
 Forum index » DIY Hardware and Software » Developers' Corner
CEM3396 Waveshapers/PWM
Post new topic   Reply to topic Moderators: DrJustice
Page 1 of 1 [9 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
earo



Joined: Apr 19, 2011
Posts: 6
Location: haifa

PostPosted: Tue Jul 30, 2013 6:59 am    Post subject: CEM3396 Waveshapers/PWM Reply with quote  Mark this post and the followings unread

Hello everybody! Smile

I'm trying to build a synth based on the CEM3396.
I'm using a 8038 based VCO to time the CEM, feeding it a +/- 5V square wave, bypassing the datasheet suggested input circuit.
This seems to work, as the DCO follows the VCO.
Most of the CV inputs work great - that is the VCA, VCF and the balance controls.

HOWEVER - the waveshapers (PWM1 & 2 and WS1 &2) do not affect the wave form at all.

Anyone might be able to clue me in as to why this is so? I tried a couple of ICs just to rule out that end, and tried tweaking the clocking square wave down to +/-2.5V as suggested in the datasheet but the wave stays the same.
Back to top
View user's profile Send private message
jackdamery



Joined: Apr 26, 2010
Posts: 73
Location: UK

PostPosted: Thu Aug 01, 2013 12:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey. Looking at the datasheet it seems you feed pin 6 a control voltage on the chip pinout diagram. But then it seems to suggest you apply two logic bits to the base of a transistor between +/- 5v to select the waveforms.

Well anyway as far as I can tell you need to select a sloped waveform before you can apply CV to pin 2 and 10 waveshapers. Can you apply 5v and sweep it via a pot to see if it makes any changes?
Back to top
View user's profile Send private message
earo



Joined: Apr 19, 2011
Posts: 6
Location: haifa

PostPosted: Thu Aug 01, 2013 1:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey - Thanks for the input!

I'm actually a little confused as to the function of the Wave Select pin (6).
My understanding was that it is used to select the combination between the two output waves. Wave A only, Wave B only, both or none.
It seems redundant to me considering there's a balance control which allows you mix them freely (minus the 'none' option obviously).

It may very well be that I missed the point of pin 6. I will definitely try what you suggested and report back!
Back to top
View user's profile Send private message
jackdamery



Joined: Apr 26, 2010
Posts: 73
Location: UK

PostPosted: Thu Aug 01, 2013 2:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi I think the wave select pin selects the base waveform - saw, triangle, sawtriangle etc and then the waveshape just affects the actual shape of these. The balance CV (pin 14) swings between the output of the two waves.
It's worth googling the cem3396 as there is quite a bit of info from the community out there.

Here for example:
http://electro-music.com/forum/post-211919.html

Check this too:
http://wolzow.mindworks.ee/analog/m1k.htm
Back to top
View user's profile Send private message
earo



Joined: Apr 19, 2011
Posts: 6
Location: haifa

PostPosted: Thu Aug 01, 2013 6:26 am    Post subject: Reply with quote  Mark this post and the followings unread

I tried your suggestion. The wave keeps its triangle shape with a slightly skewed tip. Something must have changed since I last powered this up as the PWM now kills the sound when you start applying it, otherwise the triangle wave stays the same.

Maybe implementing PWM on the driving oscillator will do the trick?

I did Google it, however apart from a couple more posts on EM (which unfortunately didn't address these issues) I couldn't find a whole lot about it.

However, I didn't get a chance to closely study the way the IC was implemented in the Matrix synths - so maybe that should be the next step.

BTW, I tried the little logic circuit suggested in the datasheet. It didn't do anything. Strange chip (or datasheet - or both..) Rolling Eyes
Back to top
View user's profile Send private message
jackdamery



Joined: Apr 26, 2010
Posts: 73
Location: UK

PostPosted: Thu Aug 01, 2013 6:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Well I just received my CEM3396 in the post today so tonight I'll join you in your struggle to find out how the hell it works Smile
Back to top
View user's profile Send private message
earo



Joined: Apr 19, 2011
Posts: 6
Location: haifa

PostPosted: Thu Aug 01, 2013 7:18 am    Post subject: Reply with quote  Mark this post and the followings unread

YES! This makes me very happy! We'll get this bugger to do what we want!

There's too much on offer in this chip to give it up!
Back to top
View user's profile Send private message
jackdamery



Joined: Apr 26, 2010
Posts: 73
Location: UK

PostPosted: Thu Aug 01, 2013 7:30 am    Post subject: Reply with quote  Mark this post and the followings unread

Haha yeh, it's really simple in reality. What are you powering it from? +12v and -5v, or +12v and -12v?
Back to top
View user's profile Send private message
earo



Joined: Apr 19, 2011
Posts: 6
Location: haifa

PostPosted: Thu Aug 01, 2013 8:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Since I'm using +/-15V for the driving oscillator, LFOs and S/H circuits I have a bunch of regulators going which are putting out +/-5V for CV control (and the negative CEM pin), and a +12V.

I know, I totally went overboard building all these modulators before actually getting the chip to function properly.. I figured I'd be able to use them elsewhere if all fails... but yes, it did seem very unlikely since the CEM seems very straight forward.

BTW, I'm feeding the second clock input a divided square wave for sub oscillation, white noise seems to work too!

Once this waveshaping business is sorted out I expect this to be a pretty powerful mono synth! Cool
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: DrJustice
Page 1 of 1 [9 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
 Forum index » DIY Hardware and Software » Developers' Corner
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
e-m mkii

Please support our site. If you click through and buy from
our affiliate partners, we earn a small commission.


Forum with support of Syndicator RSS
Powered by phpBB © 2001, 2005 phpBB Group
Copyright © 2003 through 2009 by electro-music.com - Conditions Of Use