Stormtide-Flanger LFO - some questions

Boerge · Joined: Sep 02, 2009 Posts: 82 Location: Germany

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

Designator · Joined: Jul 18, 2012 Posts: 9 Location: Northern Hemisphere

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

Regards

Boerge · Joined: Sep 02, 2009 Posts: 82 Location: Germany

Designator · Joined: Jul 18, 2012 Posts: 9 Location: Northern Hemisphere

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.

Boerge · Joined: Sep 02, 2009 Posts: 82 Location: Germany