Fudging pots. How do you halve a pots resistance?

[blearyeyes]

When you need to halve a linear pot do you need to add a resistor to each side or does one in parallel across pins 1 and 3 work? I'm a space cadet fur sur.

I'll look at the schemo to figure out the pots configuration.

I read the secret life of pots but I am a bit dense and a genius at the same time.

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[alanp]

http://www.diystompboxes.com/analogalchemy/emh/emh.html

Click linear pots.

[blearyeyes]

Great resource. Bookmarked. Thanks Alan.

[electrosonic]

It really depends on the circuit. Sometimes you can scale the resistances, sometimes it doesn't matter, sometimes you can add a resistor in series and live with the decreased range of the pot.

Andrew.

[blearyeyes]

It really depends on the circuit. Sometimes you can scale the resistances, sometimes it doesn't matter, sometimes you can add a resistor in series and live with the decreased range of the pot.

Andrew.

Well this is the symmetry pot on brejna’s Pangea and I think it needs to be what it was originally. It’s control for an unabtainium ISL8030 LFO chip.  Didn’t consider the circuit as I should have. Poop.


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[blearyeyes]

It's supposed to be 50kB all I had was 100kB. I might just pull the resistors and see. I had one 100k across 1-3 wasn't real pleased. Switched to two 50k 1-2 / 3-2  it's worse. Hmm. What do you think ?


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[blearyeyes]

Ok. It a variable resistor fed with 9v into the ICL8030. Duh. Knowledge is power. In this case 9v.


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[bsoncini]

Well putting a 100k across in parallel should give you 50k but might mess with the sweep a bit. What was so bad about it? So if it's the symmetry pot it might not be symmetrical in the middle.

[blearyeyes]

Not sure what’s going on. There is a symmetry pot on Drolos Twin Peaks and I can hear the waveform changing. There is a bias pot on the Pangea that changes the Ratio of time between positive and negative sweep. I tried a bunch of different resistor configurations and it never did much except at the extremes where it also starts to effect the speed. So I just left it at 100k instead of 50 it’s as good as it ever was. I need to look at the specs of the ICL8038 and figure out what it expects to see and what it controls at pin 3. Pretty simple.. 9v feeding a pot into another resistor before going to ISL chip’s pin three. I’ll check into it further tomorrow. Maybe I have the wrong resistor between the pot and the lfo chip. I’ve put a lot of time and effort into this one so I want it to be As good as it can be. I’m sure there is something I’m missing, like my freakin brain..lol

[bsoncini]

Ive built this voodoo vibe pedal. On mine the symmetry pot definitely changes the speed a bit. Which I think is normal.

To save you time. The resistors going to pins 4 and 5 control the rise and fall time. When equal the output should be symmetrical. I think the 39k is the rise time and 68k fall.

[bsoncini]

I had some free time and pulled my pedal out and put a scope to it.  This is in triangle mode.  The first pic is symmetry in the middle.  Second to the left.  You can see it starts to be slighly asymmetrical to the right.  The last pic is the symmetry pot to the right.  A much bigger change and slows down the lfo.

[bsoncini]

Same thing in sine mode.

[gordo]

Knowledge is power. In this case 9v.

You crack me up :-)

bsoncini, I gotta spend more time with my scope, but great visuals to demonstrate your point!!

[blearyeyes]

bsoncini,
Is that Vero or a PCB?

[bsoncini]

It is brejnas PCB.