electro-music.com   Dedicated to experimental electro-acoustic
and electronic music
 
    Front Page  |  Radio
 |  Media  |  Forum  |  Wiki  |  Links
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 
 Forum index » DIY Hardware and Software
Expected distortion with decoupling capacitor
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 1 [3 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
nullpainter



Joined: Nov 07, 2011
Posts: 32
Location: Wellington, New Zealand

PostPosted: Wed Jan 10, 2018 1:21 am    Post subject: Expected distortion with decoupling capacitor Reply with quote  Mark this post and the followings unread

Hi there,

I’m building the Devil Drone synth. For those not familiar, the guts are 3 x op amp based triangle wave signals, mixed together.

Being a good tinkerer who barely knows what he's doing, I've been playing around with tweaking the waveforms. I've just built one oscillator thus far.

I was trying to integrate the triangle waves to produce quasi-sine waves via a second op amp integrator, but was having attenuation problems at higher frequencies (this isn't the primary subject of my question, but I'm assuming that an op amp integrator shouldn't attenuate as frequencies increase?)

Given the raw output is biased at 1/2 Vcc, I thought I'd try throwing in a bypass cap to remove the DC offset to see if that would assist.

It's removing the DC offset fine, but over a few seconds my beautiful triangle wave decreases in amplitude and ends up with a flat bottom. Higher caps do the same, but take longer to manifest.

Is this what's expected? I've only got crappy headphones with me so can't tell if it still sounds reasonable.

Thanks,
M


10uf.jpeg
 Description:
Here's an image of the output with a 10uF coupling capacitor (apologies for dodgy oscilloscope photo):
 Filesize:  53.99 KB
 Viewed:  166 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

10uf.jpeg



1uf.jpeg
 Description:
And with the 1uF capacitor, just for comparison:
 Filesize:  60.69 KB
 Viewed:  175 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

1uf.jpeg



Screen Shot 17.png
 Description:
And finally, the single oscillator from the circuit. The bit in the grey box is what I've added - the rest is from the original design.
 Filesize:  66.17 KB
 Viewed:  195 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

Screen Shot 17.png


Back to top
View user's profile Send private message
Grumble



Joined: Nov 23, 2015
Posts: 1294
Location: Netherlands
Audio files: 30

PostPosted: Wed Jan 10, 2018 2:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Seen from the GND at the output, the output of your opamp is an always positive output and the capacitor will slowly be charged, bigger C's take more time to charge just like the increase of R1 will.
Looking at the filter tool: http://sim.okawa-denshi.jp/en/CRtool.php it takes about 6 sec. to fully charge the capacitor with the 100k.
When the capacitor gets charged, the diode D1 will get into non-conducting more and more thus scr..ng up your waveform.
Just remove the diode D1...

_________________
my synth
Back to top
View user's profile Send private message Visit poster's website
nullpainter



Joined: Nov 07, 2011
Posts: 32
Location: Wellington, New Zealand

PostPosted: Wed Jan 10, 2018 4:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

Of course! D1 and R1 would just be for the mixing. It now work beautifully. Thank you so much - was having a serious crisis of confidence there!
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic Moderators: jksuperstar, Scott Stites, Uncle Krunkus
Page 1 of 1 [3 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
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


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