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 Forum index » DIY Hardware and Software » Jürgen Haible designs
Stormtide-Flanger LFO - some questions
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Boerge



Joined: Sep 02, 2009
Posts: 42
Location: Germany

PostPosted: Wed Nov 20, 2013 2:54 am    Post subject: Stormtide-Flanger LFO - some questions Reply with quote  Mark this post and the followings unread

Hi all,

I'm trying to figure out how this LFO works:

http://www.jhaible.com/jh_storm_tide_1.pdf

Th LF412-part is clear, an integrator and a trigger in a loop. But then comes the CA3080: if the switch (Ramp/Dive) is closed, the outputs of both ICs are connected together. Ok, should work as long as the outputs are not overloaded (btw: would this also work with a TL082 or would that kill it?).
So I made some sims with LTSpice, exspecially for necessary changes when I use a LM13700 instead.
If the switch is open everything works as expected:

http://boergeweb.de.vu/files/Sim_sw_open.png

The output Out1 has a triangle curve, the output of the LM13700 doesn't mind in that case.

But when I close the switch (ok, the connection in the schematic Wink ) the output Out2 shows the same triangle:

http://boergeweb.de.vu/files/Sim_sw_closed.png

Where is the unsymmetric sine? Can such a thing (connected outputs of 2 OpAmps) not be simulated?

My third try was to sum the outputs with another Opamp, that works as expected:

http://boergeweb.de.vu/files/Sim_opamp_sum.png

Should I put a resistor between the outputs or would it work as in Juergen's original schematic?

headscratching greetings

Boerge

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Designator



Joined: Jul 18, 2012
Posts: 8
Location: Northern Hemisphere

PostPosted: Wed Nov 20, 2013 8:02 am    Post subject: Re: Stormtide-Flanger LFO - some questions Reply with quote  Mark this post and the followings unread

For your simulation you should add the 50k pot, the CA3080 then outputs a kind of bended triangular wave.

Regards
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Boerge



Joined: Sep 02, 2009
Posts: 42
Location: Germany

PostPosted: Thu Nov 21, 2013 4:56 am    Post subject: Re: Stormtide-Flanger LFO - some questions Reply with quote  Mark this post and the followings unread

Designator wrote:
For your simulation you should add the 50k pot, the CA3080 then outputs a kind of bended triangular wave.


Hmm... not in the sim:

http://boergeweb.de.vu/files/Sim_sw_closed_with_pot.png

In LTSpice it is the same triangle wave, not the (expected) U-shaped...
(I added a 50kOhm resistor instead a pot, but for the OTA output it's the same thing.)

But: last evening I did some soldering, and like I assumed in my last post a resistor between the LM13700- and the TL082-output did the trick. I think I will try today the pot instead my resistor and decide, which is better and what resistor value works best.

regards

Boerge

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Designator



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Posts: 8
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PostPosted: Thu Nov 21, 2013 7:12 am    Post subject: Re: Stormtide-Flanger LFO - some questions Reply with quote  Mark this post and the followings unread

Hi Boerge,

well, the virtual 'switch' is in 'Ramp' - mode, so to say, you have to delete the connection between 'out1' and 'out2' to see the effect of the OTA. To use a resistor is ok here, it forms a voltage divider together with the 620k resistor.

My guess on this LFO is, that there is a triangle wave -'Ramp', and a second wave, which is a compressed triangle, not complete sine like. The
switch just acts as a bypass. However, the labelling 'Dive' raises expectations about something more spectacular, perhaps.

IIRC there is an LFO with an OTA, that generates an asymmetrical U-shaped wave, that of the EH SmallStone phaser. There the OTA is part of the
integrator-comparator-loop, whereas here the OTA serves as a distortion/waveshaping device.
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Boerge



Joined: Sep 02, 2009
Posts: 42
Location: Germany

PostPosted: Thu Nov 21, 2013 7:58 am    Post subject: Re: Stormtide-Flanger LFO - some questions Reply with quote  Mark this post and the followings unread

Designator wrote:
well, the virtual 'switch' is in 'Ramp' - mode, so to say,


Hm... you mean ramp mode when the switch is closed? So there would be an error in Juergens drawing, the switch should change between the outputs of the OTA and the LF412?

Designator wrote:
you have to delete the connection between 'out1' and 'out2' to see the effect of the OTA.


Right, I tried it in my sim, and it works as expected...

Designator wrote:
My guess on this LFO is, that there is a triangle wave -'Ramp', and a second wave, which is a compressed triangle, not complete sine like.


Yes, the second wave is rather U-shaped,

Designator wrote:
The switch just acts as a bypass.

It's just somekind of "brute force" IMHO Wink because it connects the outputs directly. It would be better to toggle between Out1 and Out2. But now I understand Juergens comment (on http://www.jhaible.com/jh_storm_tide_flanger.html):
"The Switch performs a brute-force override from the triangle LFO when its closed"
Designator wrote:
However, the labelling 'Dive' raises expectations about something more spectacular, perhaps.

Not really Wink What the sim shows is quite that what I did expect, an U-shaped wave, similar to a full rectified AC wave (the negative half).
Ok, I will see it in the evening Smile

Thanks for your replies

regards

Boerge, wintertime is soldering time...

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