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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
utility lfo
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sonicwarrior



Joined: Dec 22, 2005
Posts: 266
Location: Cologne, Germany

PostPosted: Wed Jul 18, 2012 2:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

JingleJoe wrote:
that was a big mistake; not connecting the ground!


I was fooled by the banana jack systems. But I think they only work inside the same case this way and for connecting other cases they have a central ground connection. It seems this has to be used for the measuring equipment like oscilloscopes, too.
Maybe I should be happy I made this mistake on such a relatively simple module.
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tomcc



Joined: Dec 06, 2014
Posts: 4
Location: Australia

PostPosted: Sat Dec 06, 2014 8:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry to drag up an old thread but I have almost completed this LFO to replace a Korg MS04 pedal that had 10v Peak to peak output that had a level control to vary the output level.
If I had the various outputs on a switch that then had a 10k pot after would this reduce the level enough or would I need something else to enable control to reduce the output enough so it would not overdrive the synths filter input??
The level control was useful as it could go from mild to full blown modulation of the Korg Trident filter.
Thanks for any help.
http://www.korganalogue.net/korgms/service/ms04/ms04schematic.jpg
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roglok



Joined: Aug 28, 2010
Posts: 202
Location: uptown

PostPosted: Thu Jan 08, 2015 5:49 am    Post subject: Reply with quote  Mark this post and the followings unread

tomcc wrote:
Sorry to drag up an old thread but I have almost completed this LFO to replace a Korg MS04 pedal that had 10v Peak to peak output that had a level control to vary the output level.
The level control was useful as it could go from mild to full blown modulation of the Korg Trident filter.
Thanks for any help.
http://www.korganalogue.net/korgms/service/ms04/ms04schematic.jpg



tomcc wrote:
If I had the various outputs on a switch that then had a 10k pot after would this reduce the level enough or would I need something else to enable control to reduce the output enough so it would not overdrive the synths filter input??


what synth are you referring to? what signals does it expect?

you could attenuate the signal by a fixed ratio with a pair of resistors or by using your potentiometer wired up as a voltage divider:

Posted Image, might have been reduced in size. Click Image to view fullscreen.
(source: http://www.doepfer.de/DIY/a100_diy.htm)

another option would be a combination, so you can use the full range of your pot without overloading the input.
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roglok



Joined: Aug 28, 2010
Posts: 202
Location: uptown

PostPosted: Thu Jan 08, 2015 5:51 am    Post subject: Reply with quote  Mark this post and the followings unread

oh, and welcome
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tomcc



Joined: Dec 06, 2014
Posts: 4
Location: Australia

PostPosted: Thu Jan 08, 2015 11:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

roglok wrote:
oh, and welcome

Thanks . the synth in question is a Korg Trident.
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roglok



Joined: Aug 28, 2010
Posts: 202
Location: uptown

PostPosted: Fri Jan 09, 2015 2:40 am    Post subject: Reply with quote  Mark this post and the followings unread

i didn't dig through the schematics, but according to this image it looks like the Trident filter inputs are designed to accept a +/-5V CV signal, which is what the Utility LFO provides:

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

this means that no fixed attenuation is necessary. are you clear on how to wire the pot up as a voltage divider/variable attenuator?
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tomcc



Joined: Dec 06, 2014
Posts: 4
Location: Australia

PostPosted: Thu Jan 22, 2015 3:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the info. The pedal I was using must of used the 10k pot as a voltage divider as per you diagram to vary the level it fed to the filter section.
So to enable the LFO to be used from subtle to full blown I need to add this after the output. I am not 100% sure how to wire this up.
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tomcc



Joined: Dec 06, 2014
Posts: 4
Location: Australia

PostPosted: Fri Feb 20, 2015 10:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

Just completed wiring this up with the 10k pot as a voltage divider and it works perfectly for the Korg Tridents input.
I can switch which waveform I want and this then goes through the pot and out to the synth. It's a long time since I used the synth with an external modulator and can't believe what I have missed. Totally changes the synth sound. All I need to do is find a simple noise and S&H circuit and I have the complete package I had 30 years ago.
Thanks Ken for a great design and for those that had added their experiences.
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oculus



Joined: Oct 30, 2011
Posts: 35
Location: Iceland, Reykjavik

PostPosted: Wed Feb 10, 2016 11:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

hi there, first of all thanks ken for making this lfo available seems very interesting, i try´d breadboarding this and theres one thing iv´e been wondering about.

i´ve noticed from the lfos i have made with a skew function that often the saw and ramp waveforms dont have a hard edge to them especially on slow rates.
does anybodyknow if there is a way to make them have a harder edge ( less soft on the edges) ?

it almost feels like it has a tinybit of legato on very slow rate when fully on the saw

one thing i tryd is putting a buffer between the speed pot and the shape pot. it felt a little more solid but not much.


but the square and pulse output have hard edges and sound good its only the
saw tri ramp output i was wondering about.

thanks
kind regards
F
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