The Small Bear High-Dark LDR has changed - FYI/discuss please

[darron]

hey everybody. haven't posted hear in yonks, not much to say.

so this ISN'T an attack on Small Bear or anything btw. I highly recommend and rely on this company to get some of my best quality parts. more of an FYI and opening discussion of you are familiar with this part or have been using it.

So.... Small Bear were selling this LDR that was just amazing spec'd and really great for modulation pedals like phasers and trems etc. The operating resistance was so wide, that it went from 'hundreds of ohms' (light) to 200M+ (dark). I've bought SO, SO many different LDRs to try over the years and this one was really 'the tits': http://smallbear-electronics.mybigcommerce.com/photocell-silonex-advanced-photonix-hi-dark-nsl-7532/

they were sold out for many months at the end of last year. when they finally came back in stock i bought 100x of them. the ones that arrived looked different. my friend tried some in his univibe build and reported they worked well. this is one of the main circuits they sell the part for, so that's good news for most people.

so i loaded up 10x trems with them and found that the response on these is totally different. they look different, in that they have a lot more of that squiggle in the middle, and it's a finer line. they measure well on the meter, about as i described previously. of course, i might expect to need to make some change to my circuit, which i have done, but when i get everything balanced out well I can still find the LDR jumps much harder and there's nothing i can do to smooth it out. anyway, they are very different is my main point.


so if anybody out there was reliant on these like me, it'd really like to hear your feedback!

also, can anybody suggest an LDR source for one they really love?

i can post pics if it helps anybody.


cheers everyone

[smallbearelec]

For purposes of discussion and feedback, the manufacturer's spec for the present lot is here:

http://diy.smallbearelec.com/Library/Datasheets/UnivibePhotocell.pdf

The maker had told me that they needed to allow a slightly wider tolerance for the light resistance, and I agreed.

so this ISN'T an attack on Small Bear or anything btw.

Not taken as such.

they measure well on the meter, about as i described previously

I had a customer in Europe test samples before I went to market again, so yours is the second confirmation that the resistance range is good.

my friend tried some in his univibe build and reported they worked well.

Good to hear!

I can still find the LDR jumps much harder and there's nothing i can do to smooth it out. anyway, they are very different is my main point.

Getting consistent specs for this kind of part from lot-to-lot is known to be very difficult. I hope you come to like the result that these give you in your trem.

[darron]

I can still find the LDR jumps much harder and there's nothing i can do to smooth it out. anyway, they are very different is my main point.

Getting consistent specs for this kind of part from lot-to-lot is known to be very difficult.

yeah, consistency with LDRs is tricky! i've spent heaps of money trying out stock from all over, over a very long time.

i wouldn't want to discourage anybody from getting these for their phasers and univibes. as i said, they are as advertised in measurements, and i've got confirmation that it works well in a vibe. they are different than previously, but maybe they will even work better for people.

usually, if an LDR goes very high dark resistance, then the 'light' resistance is proportionately high too. so in the case of a trem it helps get to 'zero' volume but also keep a wide scoop. these i can definitely say are still the widest LDRs ranges ever I've ever seen, which is normally a very good thing for me.

I hope you come to like the result that these give you in your trem.

sadly, no. i'm so bummed out about it too since i have a few models which were using it, and nothing i find is as good. i understand if i need to make some changes, but i've messed around with the oscillator end and the attenuation end. even once i get all the levels zero'd out i find it still sounds more pulsed (again good specs for univibes). i was using these as a voltage divider, running the signal through the LDR and then a 100K resistor to ground after. now I find i need a 1M to 2M2 resistor to ground otherwise it will be very pulsed sounding. so about 20x more. so i'm thinking that they are even wider extending resistance range in the dark side.. even then it's sounding much more squared off without much smooth ramp in the middle.

i guess most circuits won't work like a fixed divider this way. so again, these will probably be awesome for people's projects. it's not so much a complaint, so please don't take it that way (and i don't think you directly are, thanks!) but it becomes a hugely interesting discussion point for me. i can't think of anything i could recommend high to try in your circuit first.



so i'm hoping somebody else using them can chime in, or people might tell me their other favourite LDRs. they were just a dream for me... so good. maybe don't buy 100x of them until you try them first lol. (i'll sell these to my univibe friend slowly over time, don't worry).


anybody out there using these?

[Prehistoricman]

Do you like your friend's Univibes? Perhaps it's not the LDR...?

[darron]

Do you like your friend's Univibes?

yeah he makes cool univibes      i didn't hear the new LDR, but he said he did have to make some trimpot changes and then it was okay for him.

Perhaps it's not the LDR...?

what do you mean? It's definitely a very different part now.





I don't think that anybody is really biting on this subject, so anybody feel free to delete the thread

[PRR]

If you want to explore this: get a new-part and an old-part, an ohmmeter, and a current source (9V battery and a resistor assortment). Plot I and R for both new and old. (Might save time to use a 24V supply and put the new/old LEDs in series so they have the SAME current, and have two ohmmeters to get both numbers at once.)

Comparison of curves may reveal that you just need to change the LED drive, or the audio pad impedance, to get a closer curve.

[darron]

hey Paul. I guess could graph it all out. would be interesting to see the curve responses. the optics are always incredibly sensitive to source, of course. just changing the angle of the LED very slightly can change the response.

here are the relevant parts in question for discussion sake:



R20 (100K) is the one I had to increase to about 2M2, so the LDR impedance must therefore be (generally) much higher. that's a massive jump. i've never before had to make any leaps like that. without this change, the volume would be super low and the wave would be massively humped.



of course, each LED has a different forward voltage. i played tonnes with this years ago and settled on some standard old style 5mm green LEDs (always same source). i found they had a nice smooth roll at the bottom of the wave with my clock circuit.

R18 is where I would normally adjust the brightness to match up with different LDRs. since it is dividing the voltage, it works well to tune different LEDs without messing with the smoothness of the low part of the wave or making it sound lobbed or chopped.  even different LED types be tuned to look very similar in brightness and sweep this way. this works much better than adjusting the current limit resistors (R11 + R17 = 2K)

messing with all these i couldn't get anything smooth. it's an extreme jump from on/off states. my best bet i think is searching for a sub now.



was hoping to find somebody else using this part.

[Prehistoricman]

Perhaps it's not the LDR...?

what do you mean? It's definitely a very different part now.

When you change a part in a circuit and it sounds crap, there's two things that could have gone wrong. Either the part is crap or the circuit isn't designed for that part. You've already touched on this so you're aware that the circuit does influence the results.

I agree with Paul.