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 
 Forum index » DIY Hardware and Software » The Repair Shop
{solved} What's wrong with my op amp buffer??
Post new topic   Reply to topic
Page 1 of 1 [6 Posts]
View unread posts
View new posts in the last week
Mark the topic unread :: View previous topic :: View next topic
Author Message
Beaufays



Joined: Dec 14, 2018
Posts: 4
Location: Belgium

PostPosted: Fri Dec 28, 2018 9:10 am    Post subject: {solved} What's wrong with my op amp buffer??
Subject description: something strange is going on with the simplest of opamp buffer circuits
Reply with quote  Mark this post and the followings unread

Hey,

I'm was building a buffered multi and noticed something strange on the outputs, so I went and breadboarded the simplest non-inverting buffer schematic, and look what I get... I'm at a loss here...I used tl072 and tl074 and both give the same output...
what am I doing wrong? is this because I buy the cheapest opamps on ebay? Confused


Naamloos.png
 Description:
buffer problem
 Filesize:  399.66 KB
 Viewed:  121 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

Naamloos.png



Last edited by Beaufays on Sat Dec 29, 2018 10:13 am; edited 1 time in total
Back to top
View user's profile Send private message
JovianPyx



Joined: Nov 20, 2007
Posts: 1858
Location: West Red Spot, Jupiter
Audio files: 218

PostPosted: Fri Dec 28, 2018 10:02 am    Post subject: Reply with quote  Mark this post and the followings unread

It looks like the positive portion of the signal is being clipped just above zero volts. Measure Vss and Vdd at the opamp power pins. It's possible that a bad connection prevents the full positive voltage from entering the opamp. I'm assuming that this circuit is driving nothing. If it's driving some circuit, disconnect the load and measure the waveform again.

I can't say that it won't or doesn't or can't happen, but a bad opamp is probably not the problem. If you have known good opamps, try one of those to be sure.

I won't buy electronic parts from e-bay. But then I always avoid e-bay because I just don't trust it. It is possible to get cheated, but your milage may vary.

_________________
FPGA, dsPIC and Fatman Synth Stuff

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?
corruptio optimi pessima
Back to top
View user's profile Send private message Visit poster's website
Beaufays



Joined: Dec 14, 2018
Posts: 4
Location: Belgium

PostPosted: Fri Dec 28, 2018 10:07 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey, yeah the circuit is not driving anything, but that doesn't seem to affect it anyway..
will measure power input, and buy some chips at the local shop to compare.
thx
Back to top
View user's profile Send private message
Grumble



Joined: Nov 23, 2015
Posts: 1029
Location: Netherlands
Audio files: 27

PostPosted: Fri Dec 28, 2018 4:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
It looks like the positive portion of the signal is being clipped just above zero volts.

That’s hard to tell because the scope is set at ac, so the voltage could be positive, negative or around 0volt.

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



Joined: Nov 20, 2007
Posts: 1858
Location: West Red Spot, Jupiter
Audio files: 218

PostPosted: Fri Dec 28, 2018 4:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

I agree that there's no way to guarantee that the OP set zero on the scope properly, however it is standard practice for some of us. There is most definitely clipping going on there. One of the simplest ways to account for clipping in this extremely simple circuit is for a supply line to be severely degraded with resistance or disconnect. It was only this intuition that caused me to suggest what I did. And I did not rule out a bad opamp, a blown output driver transistor could cause this as well.
_________________
FPGA, dsPIC and Fatman Synth Stuff

Time flies like a banana.
Fruit flies when you're having fun.
BTW, Do these genes make my ass look fat?
corruptio optimi pessima
Back to top
View user's profile Send private message Visit poster's website
Beaufays



Joined: Dec 14, 2018
Posts: 4
Location: Belgium

PostPosted: Sat Dec 29, 2018 10:12 am    Post subject: Reply with quote  Mark this post and the followings unread

hey,

think I found the problem. setting the scope to DC showed me the OSC was oscilating at around 12V... hence the clipping...
thanks for helping look in the right direction! Wink
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic
Page 1 of 1 [6 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 » The Repair Shop
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