DIY Vactrols - my experiences

Vactrols are getting hard to find like purple unicorns, and if you find someone you have to sell your house to get the money for them. So I decided to build my own.

In my parts bin I’ve found a bag of unknown LDR’s, they have values between 50MOhm and 50Ohm. I’ve tested a lot of different LED colors, which will give the largest range of resistance between 0.1mA and 20mA, and the best where clear white LEDs in 5mm. They give a resistance range between 90kOhm and 90Ohm. After grinding the LEDs to get a flat surface they fit perfectly in a white 5mm heatshrink tube, covered by 2 layers of black heatshrink. The open ends have to be closed by black FIMO - which is a brand name of a heat hardening modeling clay.
The Vactrols work quite well in comparison to the different types of 5C1’s according to the datasheets, the only downside is the somewhat higher forward voltage of around 2.4V, the 5C1 starting at around 1.6V, but I think this can be fixed by adding a bias voltage. I build 3 identical parts, wich interestingly measured quiet equal, so they are interchangeable.

Did someone made similar expericences? Which color do you use?

Here are some photos:


I’ve never made any but am following with interest as I’ll need some for an upcoming module.


Oh wow thems fancy DIY vactrols. Ive only dabbled with electrical tape, but the additional step to flatten the LEDs solves that slippery problem.

I wonder if hot glue (low temp) would work while wrapping in heatshrink/electrical tape. I wonder if the diffusion of the glue would inversely affect it much.

I wonder, i seem to recall seeing square head leds

And yeah this 2nd one is SMD but maybe?


The best size of the leds depends on the size of the ldr. My ldrs are round with 5mm diameter, so they fit perfect on the 5mm leds. I think the rectangular 2x3mm are somewhat small, maybe the smd version is much better, so your vactrols footprint will be much smaller.
Where would you put the hot glue, between led and ldr instead of filing down the leds?


Nice clean vactrols, not like mine !

Generaly i use some red leds of 5mm with electrical tape (a good thickness in all directions :grin:)


For those looking for ready made vactrols, SynthCube is out of stock on most of their listings but do have a couple types available. Thonk appears to have the whole VTL5Cx line. Electric Druid, Amplified Parts, and CabinTech Global all have some of them. And of course AliExpress.


I buy my vactrols from AliX. Will get the VTL5C3, next. Five pcs are $3.5 + p&p. The kind I got first VTL5C9 worked OK.

Alien Ax - Vactrols

1 Like

Beware of the Chinese Vactrols. They are fakes. So they might not have the characteristics of the originals.


Great you took some measurements! I would be interested in how close together the various vactrols you made are. The spread of the diy vactrols, if you know what I mean :slight_smile:
I also remember that some circuit descriptions said that you should not use diy vactrols because they take longer to go back to their darkness resistance. I guess that depends mainly on the LDR… did you make any measurements of that too?


I build 3 vactrols based on white LEDs and LDRs of the same charge, and yes I measured them all the same way. They are quiet equal, they start at something between 100k and 80k and go to a little under 100 Ohm. They are of course not perfectly identical, but if you take a look at the datasheets of the 5C1 series even the professional manufactured parts have a big range.

I didnt measured the timing, but I can try this the next days. I will post the results here…


Xvive vactrols — “real” ones — are Chinese. So it’s not “Chinese vactrols” to beware of, it’s fake ones — of whatever origin. But yes, there are fake ones being produced in China, Chinese fakes of Chinese real components.

Added: It’s hard to say what they have on AE is counterfeit, though, because none of them seem to be claiming theirs are from Xvive:


Though they do use the PerkinElmer / Xvive model numbers like VTL5C. And whether in fact they have specs at all like Xvive VTL5C is questionable.


I will check the ones I’ve got and also the ones that are on the way. The price was so low that I will not “loose” any money.
Btw, I should have an address to a Russian seller/maker of vactrols … :thinking:

The NSL-32SR2 is always an option, though a bit expensive.