Author Topic: Xvive optocouplers no label  (Read 1254 times)

rankot

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Re: Xvive optocouplers no label
« Reply #20 on: May 09, 2020, 04:25:02 PM »
;D sorry if I offended someone.
I mean those xvive are useless as replacement, to be used in a new design, in a repair case or "easy" component swap in a build.
They perform like an average DIY vactrol at five times the cost, but you cannot rely on the datasheet for its specs... meaning you have to work a bit to adapt the LED driver or the LDR range to get something controlled out of it.
I'm pretty upset about that, I thought those cheaper vactrols were an easy solution to implement opto control in my designs, that could be reproduced in small series.
But no luck with the ready made junk; I stick to my test rig to measure and wrap DIY vactrols with custom specs I need... long work but at the end everything acts fine, is tweakable and is reproductible.

Just take some time and measure resistance versus mA in a wide range, say 0.01mA to 10mA. Then trace a curve. You'll get some surprises.

I did few measurements of vactrols myself, but not focused on current vs resistance ratio, I actually measured response times. It was very interesting topic and you can find it somewhere here on the site. I have few of those Xvives, I will give them a run, too! Would you be kind to share your findings and comparison to original VTL5 series vactrols if possible, so we can know what to expect?
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ElectricDruid

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Re: Xvive optocouplers no label
« Reply #21 on: May 10, 2020, 10:51:29 AM »
I've just tested 5 random Xvive 5C3s.

I discovered three things:

1) The LEDs aren't all identical. We're fussing about the LDR resistance, but the LED forward voltage varies a bit too. This means that for two different devices driven on the same voltage with the same series resistor, the LED current won't be identical. That has a knock-on effect on the LDR resistance.

2) LDR resistances were spread across a range, and much tighter at the low end than the high end. Once you're to very low currents like 0.1mA, the resistance varies a lot. The range from a few K to a few hundred K is fine.

3) At the low current end, the response is very slow. The LDR is clearly following an exponential response, and it gets most of the way there pretty quickly, but the result keeps altering a little bit for a long while. The datasheet specifies dark response times to 63%, as if it were a cap charging, so this is a reasonable way to think about it.

Here's my results. I used the same resistors for each reading, so the caveat about the LEDs applies. Everything was powered on 5V.

130R/24mA:      1.9K, 1.4K, 1.,9K, 1.5K, 1.5K     (spread of x1.35)
270R/12mA:      2.7K, 2.2K, 3.1K, 2.3K, 2.5K.    ( spread of x1.4)
470R/7mA:        3.8K, 3.2K, 4.8K, 3.4K, 4.1K.    (spread of x1.5)
1K2/2.8mA:      8.3K, 7K, 10K, 8K 10.5K           (spread of x 1.5)
2K5/1.3mA:       18K, 15K, 20K, 19.5K, 23.4K.  (spread of x1.56)
5K1/0.65mA:    54K, 36K, 43K, 48K, 61K           (spread of x1.7)
12K/0.27mA:    250K, 146K, 142K, 240K, 245K  (spread of x1.76)
25K/0.14mA:   1.66M, 720K, 680K, 1.1M, 840K.  (spread of x2.4)

The results are in line with the datasheet. Reckon on resistance values varying by roughly 2:1 between devices and you'll be fine.

Yes, they vary. We knew that already. Are they unusable junk? Not at all. MPH, if you got wildly different results to this, I'd start to wonder if you haven't got some dodgy parts.

One final thing to point out is that if you use a resistor in parallel with the LDR to reduce the maximum resistance, it also reduces the variability. I used 120K in the Filter FX. Assume I drop the LED current as low as 0.27mA, so the LDR could be 140K to 250K. That gives me a final output resistance of 65K to 81K (142K||120K and 250K||120K). That's not bad at all, only 25%.

Elijah-Baley

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Re: Xvive optocouplers no label
« Reply #22 on: May 11, 2020, 04:02:04 AM »
Thanks, ElectricDruid. I really don't know how this technical information can help me, beacuse I can't get too much all that stuff! ;D
Anyway, I'm glad my thread had take you on this test, it could be useful to someone of us. ;)

Meanwhile, I tried my Xvive with the Tremulus Lune circuit I built and it works. It works perfectly? I still don't know, at slow tremolo setting I hear it a bit asymmetric, but it's the Tremulus Lune with Spacing and Simmetry controls, so I have to put the knobs on the pot and compare it with my old Tremulus Lune pedal.
(Just one issue: I follewed a layout with an external Gain/Volume pot, a 10k, but I can't get the unity bypass volume. My old layout had a 25k trimmer. Honestly, it was 100k for my mistake, anyway I found weird the external pot in this layout was 10k while the trimmer of the other layout was 25k).
«There is something even higher than the justice which you have been filled with. There is a human impulse known as mercy, a human act known as forgiveness.»
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Elijah-Baley

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Re: Xvive optocouplers no label
« Reply #23 on: May 17, 2020, 10:25:20 AM »
I think I am satisfied by this Tremulus Lune using this Xvive. But as I said I can't use the 10k Gain/Volume pot, because it doesn't push enough. a 25k was barely enough. So I use a 50k pot. Hard to compare with my first layout because my 100k trimpot, used for mistake. I just can say it was really hard to set the volume fine.
I read that the Gain/Volume pot depends from the LDR, reading teh Tonepad document. The Trimmer/Pot may need, indeed, even 100k.

So, in the end this Vactrol works ok.
«There is something even higher than the justice which you have been filled with. There is a human impulse known as mercy, a human act known as forgiveness.»
Elijah Baley in Isaac Asimov's The Cave Of Steel