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 Forum index » DIY Hardware and Software » Thomas Henry designs
X-4046 VCO Help
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tehskull



Joined: May 07, 2011
Posts: 23
Location: Kentucky
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PostPosted: Thu Jul 14, 2011 11:07 am    Post subject: X-4046 VCO Help
Subject description: VCO Calibrating
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Finished mine last night. Working on calibrating it now. I have only been doing DIY synths for about 3 months. This is my 4th completed module. Calibrating is going OK so far. When the VCO gets into higher octaves, it cuts off. Powering it off then on brings it back once the frequency is turned back down. Not sure if this is a characteristic of my 4046 or not (which is a motorola). The HF trimpot is set to maximum resistance per Thomas's calibration instructions. I am going to continue calibrating with tools now. However if anyone has any input it would be gratetfully appreciated. So far I am very happy with it. A very big thanks to Matthias and Thomas for this great project.

Thanks!

Andrew


vco2.jpg
 Description:
Calibrating the VCO with MFOS 1v\oct calibrator.
 Filesize:  2.6 MB
 Viewed:  142 Time(s)
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vco2.jpg



vco1.jpg
 Description:
Completed module
 Filesize:  2.94 MB
 Viewed:  145 Time(s)
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vco1.jpg


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fonik



Joined: Jun 07, 2006
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PostPosted: Thu Jul 14, 2011 2:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

apart from the oscillation stopping: as long as it oscillates, do you get it tuned to 1V/oct? and how many octaves do you get out of it?
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matthias
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tehskull



Joined: May 07, 2011
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PostPosted: Thu Jul 14, 2011 4:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

I am getting 8 octives just fine(my 1v\oct calibrator only goes to 8 ). It cuts off when I turn the Frequency pot up. I am trying a software oscilloscope tonight to do some more checking as i do not have a hardware oscilloscope.
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fonik



Joined: Jun 07, 2006
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PostPosted: Fri Jul 15, 2011 1:09 am    Post subject: Reply with quote  Mark this post and the followings unread

tehskull wrote:
I am getting 8 octives just fine(my 1v\oct calibrator only goes to 8 ). It cuts off when I turn the Frequency pot up. I am trying a software oscilloscope tonight to do some more checking as i do not have a hardware oscilloscope.

8 octaves? that's great.
by saying 'cut off' you say it is literally stopping to oscillate, and it does not start oscillating again when turning the coarse pot down again, until you switch off/on the module?

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diablojoy



Joined: Sep 07, 2008
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PostPosted: Fri Jul 15, 2011 3:14 am    Post subject: Reply with quote  Mark this post and the followings unread

looking at the schematic if you can get 8 octaves with a CV into the 1v/oct input it does not leave much to check as the freq pot is summed to the same opamp
check +/- 15 volts either side of freq pot R43 -100k and that R29 is 100k
if all that checks OK then you do have something very strange going on.
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fonik



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PostPosted: Sat Jul 16, 2011 1:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

problem solved. he swapped the motorola for an NXP!

so the motorola does not seem to be a good choice all the time!?

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matthias
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bubzy



Joined: Oct 27, 2010
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PostPosted: Sat Jul 16, 2011 11:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

im wondering if the motorolas i have are the problem too. just cant find NXP's anywhere. any clues?
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Level5



Joined: Feb 16, 2007
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PostPosted: Sat Jul 16, 2011 11:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Mouser P/N: 771-HEF4046BPN
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alkopop79



Joined: Aug 21, 2008
Posts: 44
Location: London

PostPosted: Wed Jul 10, 2013 11:08 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm planning to use a 4046 to build a VCO. I wonder if I can change the PWM somehow? I've seen the Thomas Henry VCO but it seems the duty cycle is altered by an external circuit. How does that work?
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fonik



Joined: Jun 07, 2006
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PostPosted: Wed Jul 10, 2013 1:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

thomas cheats the 4046 to output falling and rising ramps which are combined to a triangle.
so he actually created a triangle core VCO around the 4046.
the triangle is fed to a tri2sin waveshaper.
the sine is then fed to a comparator to get the PWM.

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matthias
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alkopop79



Joined: Aug 21, 2008
Posts: 44
Location: London

PostPosted: Thu Jul 11, 2013 12:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you! so what waveform the 4046 is capable of producing?
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