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
  mosc Live music with Twyndyllyngs - Bill Fox and Howard Moscovitz
Please visit the chat
 Forum index » DIY Hardware and Software » Thomas Henry designs
dual 8038 VCO cross-talk
Post new topic   Reply to topic Moderators: Scott Stites
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
fonik



Joined: Jun 07, 2006
Posts: 3755
Location: Germany
Audio files: 23

PostPosted: Wed Sep 26, 2007 8:53 am    Post subject: dual 8038 VCO cross-talk
Subject description: possible reasons
Reply with quote  Mark this post and the followings unread

hi all,

as you might already know i built a dual 8038 VCO recently. the layout is that way, that all ICs are placed in a row utilizing one half of each IC for each VCO.

now i observe a cross-talk between both VCOs, audio and cv. i wonder if the described usage of the ICs might be the cause? any suggestions or experiences?

BTW i like the sound of the VCOs very much and it would be a shame if i would have to build it again, which would have to wait for a couple of weeks...

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
bubblechamber



Joined: Nov 04, 2006
Posts: 276
Location: NYC
Audio files: 1

PostPosted: Wed Sep 26, 2007 10:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

i've had cross talk in twin oscillators coming from a shared ground bus. it cleared up when I stopped sharing the power and ground between the 2.
david
Back to top
View user's profile Send private message Visit poster's website
fonik



Joined: Jun 07, 2006
Posts: 3755
Location: Germany
Audio files: 23

PostPosted: Wed Sep 26, 2007 11:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

sounds consistent. so i will do a better neat and decend job and solder in some decoupling caps. hope that will help...
_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Etaoin



Joined: Jun 30, 2005
Posts: 760
Location: Utrecht, NL

PostPosted: Tue Oct 09, 2007 1:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Matthias, did you solve this?
_________________
http://www.casia.org/modular/
Back to top
View user's profile Send private message Visit poster's website MSN Messenger
fonik



Joined: Jun 07, 2006
Posts: 3755
Location: Germany
Audio files: 23

PostPosted: Tue Oct 09, 2007 9:06 am    Post subject: Reply with quote  Mark this post and the followings unread

not yet! i am currently struggling with a loose contact or hairline crack on my wasp vcf proto pcb!

i will try decoupling caps next week. stay tuned...

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Thomas Henry



Joined: Mar 25, 2007
Posts: 298
Location: Southern Minnesota
Audio files: 2

PostPosted: Wed Oct 10, 2007 8:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi all,

I've been really swamped with school work lately. But I just had to jump into this thread.

My experiences over the last thirty years have made it very plain to me that dual VCOs are inherently dangerous as a general rule. The tiny currents involved mean that any sort of variation through the power supply or through messy wiring or parallel traces on a PCB will lead to tuning disorders, unintentional syncing, and more.

I really think that VCOs should only be built as single units.

However, if you're going to risk a dual, I would recommend:

1. Don't share dual or quad op-amps between the units, and

2. Be sure to use a star-configuration for wiring the power supply lines. This is extremely important, even more important than the decoupling caps. VCOs in any system have a tendency to lock or interact, but a star power supply connection will minimize it.

Anyway, that's my two-cents worth,

Thomas Henry
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3755
Location: Germany
Audio files: 23

PostPosted: Thu Oct 11, 2007 4:40 am    Post subject: Reply with quote  Mark this post and the followings unread

thank you thomas for your valuable comments.

so i think i will do the following: i will design a layout for a dual 3038 VCO whereby the VCOs are only sharing the matched transistor array (which is a passive device anyways) and the power connection header...

so STOP everybody! hope i am able to achieve it next week (i am on vacation this week and have no access to the machine storing the files).

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Thomas Henry



Joined: Mar 25, 2007
Posts: 298
Location: Southern Minnesota
Audio files: 2

PostPosted: Fri Oct 12, 2007 6:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hiya Fonik,

I probably came across as a bit heavy-handed in my last post, and I hate it when the so-called "old-timers" lay down pronouncements. I should have given some reasons for my prejudices.

But I remember building a three VCO unit back in 1982 or thereabouts for a friend. The idea was have a lush sound with the VCOs slightly out of tune with each other for a natural chorusing effect.

I spent hours, days, even months trying to debug the system and keep the VCOs from syncing to each other. I can't remember all the details, but I do recall that the star configuration to the power supply was a major part of it.

Also, much later I remember doing a shared quad op-amp on another circuit and the square wave interacted with the triangle wave within the package.

So anyway, I don't usually do dual units myself nowadays, but you might consider these points as you lay out a PCB.

Then again, I used to do PCBs by hand. Perhaps the newer software has clever ways to route the traces to avoid these problems.

Thomas Henry
Back to top
View user's profile Send private message
fonik



Joined: Jun 07, 2006
Posts: 3755
Location: Germany
Audio files: 23

PostPosted: Sat Oct 13, 2007 3:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thomas Henry wrote:
I probably came across as a bit heavy-handed in my last post,...

not at all! Cool

Quote:
Then again, I used to do PCBs by hand. Perhaps the newer software has clever ways to route the traces to avoid these problems.

i tried some demo layout software with autoroute functionality. i personally don't think it makes things easier, the software is not clever at all. cleverness is probably related to creativity which is hard to define by rules a software may need? don't know.
i just try to follow the schematic/circuitry.

_________________
Posted Image, might have been reduced in size. Click Image to view fullscreen.
cheers,
matthias
____________
fonitronik at
FlickR (pix) / SoundCloud (sounds) / YouTube (vids) / Vimeo (vids) / facebook (news)
Back to top
View user's profile Send private message Send e-mail Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic Moderators: Scott Stites
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 » Thomas Henry designs
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