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 Forum index » DIY Hardware and Software
circuit for dual output LFO with 180 degree phase shift?
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ALAS



Joined: Oct 14, 2013
Posts: 8
Location: Philadelphia

PostPosted: Wed Aug 13, 2014 6:29 am    Post subject: circuit for dual output LFO with 180 degree phase shift? Reply with quote  Mark this post and the followings unread

Hi,

I am looking for a (hopefully fairly simple) LFO circuit that would output two waveforms 180 degrees apart.

Also a possibility: a circuit for inverting the output of an initial LFO.
Also a possibility: a circuit for phase shifting the output of an initial LFO

I found a fairly simple circuit that gives you three 120 degrees apart
(http://www.schmitzbits.de/triphase.html)
and I know that quadrature LFOs also exist. For example, I found this one (http://yusynth.net/Modular/EN/QUAD-LFO/index.html)
which seems really cool and does indeed contain LFOs 180 degrees apart, but is more complicated than what I need.

Can anybody point me towards a dual version?

Thanks!
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thermionicjunky



Joined: Dec 07, 2006
Posts: 72
Location: san francisco

PostPosted: Wed Aug 13, 2014 6:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Inversion is a simple solution that will do exactly what you want.
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elmegil



Joined: Mar 20, 2012
Posts: 1504
Location: Chicago
Audio files: 14

PostPosted: Wed Aug 13, 2014 2:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

thermionicjunky wrote:
Inversion is a simple solution that will do exactly what you want.


Depends on the waveform..... Sine, Triangle, Square? Definitely.

Ramp/Saw, pulse? Not so much....
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ALAS



Joined: Oct 14, 2013
Posts: 8
Location: Philadelphia

PostPosted: Wed Aug 13, 2014 10:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

I would be happy to just use symmetrical waveforms and invert them. I don't know how to find an appropriate circuit to do the inverting though-- I'm not exactly sure what to search for even. Any examples?
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elmegil



Joined: Mar 20, 2012
Posts: 1504
Location: Chicago
Audio files: 14

PostPosted: Thu Aug 14, 2014 5:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Run it through an inverting op amp:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

make the two resistors the same (say, 20K or so) and you have unity gain and an inverted signal. Op amps require a bipolar supply (most of the time, there are ways around that but can get more difficult to work with audio signals).
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gdavis



Joined: Feb 27, 2013
Posts: 159
Location: San Diego

PostPosted: Fri Aug 15, 2014 9:57 am    Post subject: Reply with quote  Mark this post and the followings unread

http://yusynth.net/Modular/EN/LFO/VC-LFO1.html

Includes an inverted output.

_________________
My synth build blog: http://gndsynth.blogspot.com/
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okelk



Joined: May 08, 2014
Posts: 29
Location: Vienna

PostPosted: Thu Sep 04, 2014 3:01 am    Post subject: Reply with quote  Mark this post and the followings unread

have a look at this thread:
http://electro-music.com/forum/topic-32372.html

pick any lfo ( I really like the 8k lfo...don't forget the decoupling caps), put the opamp inverter mentioned above on the output(s), add led drivers to taste ( http://www.electro-music.com/forum/topic-49449.html ) and you have what you need.
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