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 Forum index » DIY Hardware and Software » YuSynth
New module at yusynth.net : Quadrature VC-LFO
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PHOBoS



Joined: Jan 14, 2010
Posts: 4540
Location: Moon Base
Audio files: 633

PostPosted: Fri Nov 24, 2017 10:57 am    Post subject: Reply with quote  Mark this post and the followings unread

yes it has 2 anodes but also 2 cathodes, it's just 2 LEDs antiparallel in 1 housing.

The problem you're having is that if 1 output goes positive the other will go negative (which would make it work)
but because of the transistor drivers the negative side is basically floating. Imagine having diodes between the
outputs and the LEDs with their cathodes connected to the LED pins.

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unrecordings



Joined: May 10, 2017
Posts: 4
Location: Sheffield

PostPosted: Fri Nov 24, 2017 11:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Now I think that makes sense - thanks
I tried the LED across pins 4 & 8 of U3 - works a treat, but i'm not sure about causing problems down the line when i'm pushing this module and driving lots of other modules with it.
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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Fri Nov 24, 2017 11:39 am    Post subject: Reply with quote  Mark this post and the followings unread

You could add 2 opamps (configured as voltage followers) as buffers for the LEDs.
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unrecordings



Joined: May 10, 2017
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PostPosted: Fri Nov 24, 2017 1:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
You could add 2 opamps (configured as voltage followers) as buffers for the LEDs.


thanks, but that takes it to another level really, when a single LED is just fine and I could just hang a bipolar LED from the main output if I really wanted one

but thanks again for the wise words
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charonme



Joined: Mar 05, 2019
Posts: 1
Location: Slovakia

PostPosted: Tue Mar 05, 2019 4:02 am    Post subject: Reply with quote  Mark this post and the followings unread

I breadboarded it with the caps = 1uF for extra slow oscillation, I'm getting around 0.002Hz with ~0.1uA injected into the LM13700 and almost 10Hz with 1mA (and >21 minutes when the current is <0.1uA below the range of my multimeter).

btw is there any significance in the LM13700 linearizing diodes being reversed on the OTA symbol in the original schematic? http://yusynth.net/Modular/Commun/QUAD-LFO/Quad-LFO-v2-sch-thumb.gif

BTW the core of the circuit somewhat reminds me of a state variable filter, are there any substantial differences? If this could work as a SFV, where would the input be?
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