# Circulator Phaser - Dual LED



## Many__Of__Horror (Dec 28, 2019)

With the issues people have been having with the LFO LED on this pedal, I'd like to modify it to have a single colour LED flash as the LFO at all times (like the bi-colour LED currently does in bypassed or engaged) and add a 2nd LED that is purely an indicator for the effect being on/off. Thinking like the Walrus Julia does for an example.

Could I just swap out the bi-colour LED on the PCB with a regular LED for the LFO. Then is there a way to offboard wire another into the 3PDT switch. An example on what goes where etc would be great for a visual learner like me....

Cheers


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## Chuck D. Bones (Dec 28, 2019)

That will help with the LFO loading.  I'll describe the mod in words and you can sketch it out. 

On the silkscreen, the bicolor LED is labeled R & G.  Install the LFO indicator LED between R and the middle LED pad, with the LED's anode (longer lead) to the middle pad.  Increasing R33 to 10K will also help with the LFO loading, but will make the LED less bright.

The ON/OFF LED gets wired from the G pad (LED cathode) to +9V (LED anode).  R100 sets the brightness of this LED and has no effect on LFO loading.


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## Many__Of__Horror (Dec 28, 2019)

Brilliant. I think I'll put a 10K trimmer on R33 in this case.
Thank you for the explanation. Now to research more on how the LFO works out of interest.


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## Chuck D. Bones (Dec 28, 2019)

R33 and the LED are actually part of the LFO and the LFO won't work without them.   Making R33 too big or too small could stop the LFO.  Don't dial the R33 trimmer down to zero or you could overstress the LM13700.  I'd put a 1K in series with the trimmer for safety.

Once you have dialed in the R33 trimmer, check the LFO at min & max RATE, min & max SWEEP to make sure it runs under all settings.

The LFO circuit is different from every other pedal I've come across.  You need to understand how the LM13700 works to make any sense of the LFO.


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## Many__Of__Horror (Dec 28, 2019)

Chuck D. Bones said:


> R33 and the LED are actually part of the LFO and the LFO won't work without them.   Making R33 too big or too small could stop the LFO.  Don't dial the R33 trimmer down to zero or you could overstress the LM13700.  I'd put a 1K in series with the trimmer for safety.



Good idea thanks


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## Many__Of__Horror (Dec 28, 2019)

Just thinking the best way to physically solder the 1K resisitor with the 10K trimmer. I usually use a single pin header in the PCB along with a PedalPCB trimpot board to mount a trimmer. Where would you solder the resisitor to? Does it matter if I solder it to the underside of the board or over the top of the trimmer. i.e connecting to either end of the single pin header?


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## Chuck D. Bones (Dec 28, 2019)

Either end of the trimmer works.  But... When you're all done getting the pedal working and the trimmer dialed-in, you don't really need the trimmer any more.  It can be replaced with a fixed resistor.  Why not just solder two wires to the resistor pads and solder the trimpot and 1K resistor to the other end of the wires?  Get it all adjusted the way to like on the bench, then remove the wires, resistor & trimpot, measure them, get the nearest standard resistor value and solder _that _into the board. Just sayin'...


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## Many__Of__Horror (Dec 30, 2019)

Chuck D. Bones said:


> On the silkscreen, the bicolor LED is labeled R & G.  Install the LFO indicator LED between R and the middle LED pad, with the LED's cathode (shorter lead) to the middle pad.  Increasing R33 to 10K will also help with the LFO loading, but will make the LED less bright.
> 
> The ON/OFF LED gets wired from the G pad (LED cathode) to +9V (LED anode).  R100 sets the brightness of this LED and has no effect on LFO loading.



Just confirming the LFO LED orientation is correct above. I ask because the bicolour LED is supposed to be common anode. I would assume the middle pad is therefore anode leg of the LED.
Above you mention the Cathode leg going to the centre. Does it change the layout with these changes?


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## Many__Of__Horror (Jan 1, 2020)

Still not having much luck with this mod. The effect is working perfectlt I just cannot get the LFO LED to work with the mod. When I set it up with 1K resisitors on R33 & R100 and a common anode bicolour. I get 1 colour only flashing with the LFO rate. But this mod only the On/Off indicator illuminates.
I have tried a 4K7 resisitor in R33 as well with no change.
Hopefully You can make heads and tails of my picture


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## Many__Of__Horror (Jan 2, 2020)

Well I think I'm going to call this done. I have a standard LED connected to Mid (Anode) & G (Cathode). When the effect is bypassed I get no LED. When effect is engaged I get LFO pulsing on the LED. So it indicates when on and shows the LFO pulse so I'm happy enough with that.
Cheers for all the help Chuck.


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## Chuck D. Bones (Jan 3, 2020)

I screwed up, the middle pad is the ANODE, duh.  The way I had written the instructions, the LFO LED would have been installed backwards.  I went back and corrected my post from Saturday, 12/28.  The LFO LED will work if you wire it per the updated instructions.  Sorry about that! ?


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