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 Forum index » DIY Hardware and Software
EFM LFO 3512
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wackelpeter



Joined: May 05, 2013
Posts: 130
Location: germany
Audio files: 6

PostPosted: Tue Apr 07, 2015 2:08 pm    Post subject: EFM LFO 3512 Reply with quote  Mark this post and the followings unread

Just tried to build this LFO on stripboard. I have omitted the VCA part of the whole Thing and thus used for U1b an TL071.

http://www.modular.fonik.de/files/EFMforum/orgEFMfiles/3500er/3512_LFO.pdf

Well i'll post this because i have some Problems and would be thankful for some advice or help on Troubleshooting.

The FET seem to cause some Problems here...
With the FET installed as per schematics the LFO doesn't cycle... already switched D and S as i found out that there are some DSG and some SDG pinout.
Ah important note: i didn't used a 2N5460 but a 2N5461 instead...

When i disable Drain and Source of the FET from the board all Looks fine... range and skew function do work but when i turn the FET in it stops and i'll have a steady 10V Output at the triangle...

So far i have have at the Output of the Comparator a Signal near power rails when a gate is applied...
When i turn the Gate of the FEt directly to Pin6 of the TL071 i measure the following:
5V on Gate Input ...Triangle cycles (+/-4V)
0V on Gate Input... 10V steady output

Using the Gate of the FET after the Diode and Cap it doesn't do anything...

hmm... any idea where to start?

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wackelpeter



Joined: May 05, 2013
Posts: 130
Location: germany
Audio files: 6

PostPosted: Wed Apr 08, 2015 3:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Seems as i got it the totally wrong way... This LFO is a gated LFO... means it only cycles when a gate/certain treshold is applied to the comparators Input? correct? i#m sure now, that#s the way it's supposed to be used...
From what i've measured (only works when i put the Gate of the FET directly to the comparators Output) i get when using a triangle wave as Input of the comparator the LFo cycling above a treshold voltage of 1V... below 1V a steady 10V voltage at the triangle out...

okay seems as i have to dive deeper into this circuit...

what i would like to get is adding a variable treshold to the comparator to start the LfO at variable voltages coming from an keybd.CV, LFO or EG...
(this idea i think i can "steal" from Ian Fritz's TGTSH curcuit) or just adjusting the Control so that it cycles autonomous without an CV fed to the Input...
(the keybd. idea sounds interesting... imagine having some notes without and some with Portamento, vibrato or filter effect... curious how that would sound)

Also i would like to get rid of the 10V when the LFO stopped... i fear i could damage some of my modules with a steady 10V voltage... 0V seems to be the better choice...

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