Need LFO Help Zombie Chorus /Lich King

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Carvindc125
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Post by Carvindc125 »

I have been struggling for a week now trying to get this LFO to LFO!
I have it on the breadboard.
ideally I would like to use a different LFO that is bipolar powered but its wave is + to - V someone told me the CD4046 chip and not take -V at its pin 9

So I decided to go with unipolar power on the LFO and use the Zombie/ Litch King LFO
Problem is I cant get it to work. I only get a steady voltage out of the output.
below is a pic of my breadboard and the LFO im trying to make.
If someone has gotten this LFO to work before on the breadboard could you please post your layout? I feel that since im so used to using Bipolar powered LFOs I might be making a mistake.

FYI Not in the picture but was connected during testing is +9V to pin 8 Pin 4 is Grnd Pin 2 is Vref (4.5V)
Ideally If the CD4046 can not take an LFO that's bipolar powered then I need it to run on +6 on Pin 8 and Vref of +3
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Lich_LFO.png
LFO Labeled.png

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The G
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Post by The G »

I see two issues:
  1. First of all, you need to create a VREF by dividing V+. On my breadboard I used 10kΩ resistors and a 100μF capacitor instead of a 10kΩ trimpot between 4k7 resistors and a 47μF capacitor as in Lich King's schematic (talking about R12, VR3, R13 and C11 in www.diyguitarpedals.com.au Lich King documentation, see below).
    Only pin 4 of the IC gets V-, besides the capacitor and a resistor of the voltage divider creating VREF.
  2. After you fix that, the LED may be too much of a load for the poor TL062, especially in that particular circuit. IMO, it needs a buffer.
Part of the Lich King build documentation by www.diyguitarpedals.com.au
Part of the Lich King build documentation by www.diyguitarpedals.com.au
Look at me testing the LFO here:




Oh, and I used a 47nF capacitor instead of the 10nF one to slow down the oscillation enough to be read by my multimeter. Notice that the voltage is referenced to VREF, so the measured voltage goes from, let's say, -1.7V to +1.7V.

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Carvindc125
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Post by Carvindc125 »

The G wrote: 01 Mar 2021, 18:14 I see two issues:
  1. First of all, you need to create a VREF by dividing V+. On my breadboard I used 10kΩ resistors and a 100μF capacitor instead of a 10kΩ trimpot between 4k7 resistors and a 47μF capacitor as in Lich King's schematic (talking about R12, VR3, R13 and C11 in www.diyguitarpedals.com.au Lich King documentation, see below).
    Only pin 4 of the IC gets V-, besides the capacitor and a resistor of the voltage divider creating VREF.
  2. After you fix that, the LED may be too much of a load for the poor TL062, especially in that particular circuit. IMO, it needs a buffer.
IMG_20210301-202224.png

Look at me testing the LFO here:




Oh, and I used a 47nF capacitor instead of the 10nF one to slow down the oscillation enough to be read by my multimeter. Notice that the voltage is referenced to VREF, so the measured voltage goes from, let's say, -1.7V to +1.7V.
Thanks!
Actually I mentioned in that post in the Pic I left out the voltage divider for Vref and explained how I had those hooked up in testing.
"FYI Not in the picture but was connected during testing is +9V to pin 8 Pin 4 is Grnd Pin 2 is Vref (4.5V)
Ideally If the CD4046 can not take an LFO that's bipolar powered then I need it to run on +6 on Pin 8 and Vref of +3"

As for the actual issue you are correct. It was the LED. I upped the CLR to 4K7 and it works now. I use a TLO72 IC. However it might still need a buffer. What do I need in order to add a buffer?
I say this because now I have a new issue. The Depth pot will flatten the triangle wave to just a flat so its working too good? Or the LED is still clamping to much even with a 4K7 resistor? I can remove the LED and see if the issue is still there.
Thanks for all your help on this.

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Post by VivMeLol »

This Square / Triangle oscillator is very standard Schmitt trigger and integrator

The left Opamp's output will go high the moment the pin 3 non inverting input is Vref + very small hysteresis amount maybe 0.00001V

and it will go low the moment the pin 3 non inverting input is Vref - very small hysteresis amount

if we put an LED with CLR from Pin 7 to ground, the LED can act as a voltage clamp and stop the left Opamp's Pin 3 from going high enough to trigger the Schmitt trigger.

So either we get rid of the LED

Or increase the CLR to maybe 5K instead of 220 Ohms so that the effect of the clamp is lessened

Or play around with R15 to give more signal to the Schmitt

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Post by VivMeLol »

The G wrote: 01 Mar 2021, 18:14 Notice that the voltage is referenced to VREF, so the measured voltage goes from, let's say, -1.7V to +1.7V.

Thank you very much !!!

Could you please confirm

What was your power supply voltage ?

Could you make a video of output of the left IC Pin 1 (or post the max and min voltages you see)

Thank you

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The G
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Post by The G »

Carvindc125 wrote: 04 Mar 2021, 14:16[...]
Actually I mentioned in that post in the Pic I left out the voltage divider for Vref and explained how I had those hooked up in testing.
"FYI Not in the picture but was connected during testing is +9V to pin 8 Pin 4 is Grnd Pin 2 is Vref (4.5V)
Ideally If the CD4046 can not take an LFO that's bipolar powered then I need it to run on +6 on Pin 8 and Vref of +3"
[...]
My bad, I was thrown away by reading - = Vref in the breadboard image.

My power supply was a 9V battery putting out around 8.95V.
It got replaced on the breadboard, so I cannot do new measurements in the near future.
In the video the lead of the multimeter was connected to the cursor (pin 2) of VR2, with VR2 in its maximum position.
My multimeter does not have a min/max feature and the voltages I saw ranged from around -1.6V to around +1.7V. The real voltages could be higher in absolute value if we count the multimeter sample rate in.

Circuits that come to mind for isolating the LED are op amp repeaters or BJT buffers (use big values vor R2 and R3):
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led_buffers.png
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