do LDRs go to zero?

[kvb]

I'm messing with the retrofit. I have decent results with radio shakk ldrs and some super bright leds.
connected to the wah-pot I get 250k - heal down, and .5k toe down.
I'd like to have zero.

I get similar results with a vtl5c2.

parallel resistors just alter the high max.

any suggestions? - other than telling me not to bother

[dr]

....I haven't found any lower than 500 ohms, myself-but I have mounted them in parallel in my Neovibe, and am happy with the range I get with them....I found them at Jameco-I forgot the part number, but they were the ones with the lower ohm ratings...

[Seljer]

nope they dont, they usually have a couple of kohms resistance when fully illuminated

but in the retrofit with the LDR like on the geofex article, you have another regular resistor connected as the other part of the pot, so as you change the brightness, the ratio between them as a voltage divider changes, which is the reason it works
http://geofex.com/Article_Folders/wahpedl/wah11.gif

example with a 100k resistor
so with it bright you have something like .5k/(100k+.5k) = very little, under 1%
and with it dark you have 250k/(100k+250k) = 70%

(might be good to try a 100k trimpot for that resistor to find the optimum range)


though this setup of replacing a pot with and LDR might not work in all applications

[puretube]

there are optocouplers, that guarantee <60 Ohm "light resistance" (=20mA thru LED),

but that was before RoHS


some famous amp manufacturers use them for switching...

[kvb]

I tried having an LDR at both resistor positions.

I put 9v at the pot's wiper.

the outside poles go to the two LDRs.

at toe down the top resistor is dark/ high resistance; the bottom resistor is light/ low resistance
at heal down the top resistor is light/ low resistance; the bottom resistor is dark/ high resistance

now there is a significant ratio.


I'm not sure that this is ideal, but it sure is different.  The wah now sweeps from way lower down (off the deep end low).

[KMS]

I've never seen one go to zero.

I have tested many from Radio Shack and it is a grab bag event where you must test each one because of the variance in quality of the LDR.

If you get a bright LED (Blue or Red) and cherry pick about 5 packs of LDRs you should be able to get it down to 40ohm light resistance....but be carfull and don't forget to check the dark resistance.....in many cases I have noticed a lower dark resistance accommodates the LDRs which also have a lower light Resistance....but not all of them are like that.

[sfr]

I'm not sure that this is ideal, but it sure is different.  The wah now sweeps from way lower down (off the deep end low).

I'd assume that's because some of these LDRs can go up to Megaohms of resistance - try a resistor in parallel across the the lugs of the LDR to keep it from going that high (or possibly, simply compensate with the positioning of the wah pot)

[Brian Marshall]

Ive found the vtl5c stuff varries quite a bit.  a vtl5c2 can hit 1k at anywhere between 1mA and 20mA.  At least they are big enough that you can write on them with a pencil when trying to match them.  Unlike jfets.