LED forward voltage tolerance

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,656
Location
Norfolk - UK
Oh no, CdS is toxic. But it's not offensively toxic when used in small quantities. A CdS cell has only a tiny amount of CdS in it. So it's not bad like lead solder which is very toxic in a bioacummulation way and accounted for significant mass of a circuit board when it was used.

Note that chemical analogies do not work as expected. If you look at a periodic table, Sulfur is in the same column and directly under Oxygen and Cadmium is in the same column and directly under Zinc but Zinc Oxide has very low toxicity (it's used in lots of house hold products and even as a food additive) but CdS is definitely toxic. You would not want to make a hand cream out of it or sprinkle it on tacos.
It is not clear to me that being toxic per se is enough for CdS to be banned. For sure there are millions of toxic substances in ue in everyday life but they are not all banned. I know Cadmium itself is banned in the EU but is CdS specifically mentioned? How toxic is it comparaed to, say, bleach?

Cheers

Ian
 

gyraf

Well-known member
Staff member
GDIY Supporter
Moderator
Joined
Jun 4, 2004
Messages
10,732
Location
Aarhus, Denmark
the LDR part of the vactrol (for technical reasons) always contains cadmium in amounts exceeding what can be rohs-certified for sale in EU (100ppm, 0.01%) - Compliance FAQs: RoHS

Several companies - including xvive - has claimed to have ROHS-compatible solutions, but it always turns out to be outright lies. A company named Macron even presented falsified laboratory records to the EU group in charge of rohs/weee

So, for now, there's no solution that I'm aware of. But I'm hugely interested if something real shows up - I really miss being able to do optical compressors..

/Jakob E.
 

Bo Deadly

Well-known member
Joined
Dec 22, 2015
Messages
2,993
Location
New Jersey, USA
I know Cadmium itself is banned in the EU but is CdS specifically mentioned?
No idea but if they have banned an entire element, that would include all molecules containing that element.

There are practical limitations to the law. They would have to specifically allow for a certain amount of CdS in a certain type of products under some confluence of circumstances. Otherwise someone could, in theory, create a product with a whole bunch of CdS in it and that would be ok to the letter of the law. My guess is that lawmakers are not particularly concerned with a handful of people making one-off electronic devices. They're concerned with large industrial manufacturing.

How toxic is it comparaed to, say, bleach?
Again your chemical comparisons are not ideal. Bleach is not toxic. It's a strong base that will dissolve organics but it doesn't give you cancer.
 

JohnRoberts

Well-known member
Staff member
GDIY Supporter
Moderator
Joined
Nov 30, 2006
Messages
23,695
Location
Hickory, MS
Again your chemical comparisons are not ideal. Bleach is not toxic. It's a strong base that will dissolve organics but it doesn't give you cancer.
I love this place...

WWW said:
Gargling or drinking bleach most likely would cause superficial burns in the esophagus. The CDC notes that adults attempting suicide by ingesting liquid bleach have shown that "a lethal dose" of sodium hypochlorite can vary from 7 to 18 ounces at concentrations of 3 percent to 12 percent. 3. Don't bathe in bleach


Toxic? A strong base will still burn ya... Nice of the CDC to provide lethal dose advice. I remember a dumbass back in the 70s who tried to commit suicide using aspirin. He mainly gave himself a bad headache.

For several weeks now I have been trying to scrub hard water stains off my shower walls. I am careful about not mixing chlorine based cleaning products with acids that could release chlorine gas (don't forget WWI while I was not there).

I have had some success using Glycolic acid (ZEP) and lots of elbow grease (lots of scrubbing). Despite removing lots of rust colored water stains, I can now see more to clean. This is a classic "hippie haircut"*** scenario. It looks cleaner to me, but still isn't completely clean.

JR

*** Hippie Haircut.... the proverbial case of the long haired hippie with hair growing down to his butt who gets a speeding ticket and court appearance. He decided out of respect for the judge and hopeful to win leniency he gets his hair trimmed to only shoulder length. A remarkable improvement to people who knew what he looked like before, but to the judge, he still looks like a long haired hippie. :unsure:
 

blakeyboy

Well-known member
Joined
Sep 29, 2005
Messages
59
Location
UK
Power transistors were full of beryllium supposedly, and no-one banned those....

These 'vactrols'- are they the ones Neve used in their Necam faders and 618 opto boards when they ran out of
CLM6500's? I've got some somewhere...
 

scott2000

Well-known member
Joined
Feb 21, 2015
Messages
2,978
Location
Sunny...Sometimes Florida- USA
I have had some success using Glycolic acid (ZEP) and lots of elbow grease (lots of scrubbing). Despite removing lots of rust colored water stains, I can now see more to clean.
Zep is pretty awesome. EaCo Chem Britenol HD is a big step above but it's pretty potent. Actually pretty safe, safer than their One Restore which will etch the glaze from tile, but cuidado still.
Oxalic acid (barkeeper's friend has this), White Ox...etc.....is great for rust stains....
 

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,656
Location
Norfolk - UK
I just bought a bunch of LEDs. This evening I tested 20 nominally identical RED LEDs with my Peak ATLAS tester which feeds a precise 5mA though them. The forward voltage drop ranged from 1.88V to 1.92V which is a range of just 0.04 volts. This compares to the 0.2 volt range I saw when testing five Vactrols. I remain suspicious of the Vactrols.

Cheers

Ian
 

abbey road d enfer

Well-known member
Staff member
GDIY Supporter
Moderator
Joined
Jan 22, 2008
Messages
14,702
Location
Marcelland
I just bought a bunch of LEDs. This evening I tested 20 nominally identical RED LEDs with my Peak ATLAS tester which feeds a precise 5mA though them. The forward voltage drop ranged from 1.88V to 1.92V which is a range of just 0.04 volts. This compares to the 0.2 volt range I saw when testing five Vactrols. I remain suspicious of the Vactrols.
As I said earlier, you shouldn't worry about that, because it's the R vs I curve that is important.
The actual tolerance on the LDR is way larger.
You don't intend to use voltage-drive for the LED, do you?
 

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,656
Location
Norfolk - UK
As I said earlier, you shouldn't worry about that, because it's the R vs I curve that is important.
The actual tolerance on the LDR is way larger.
You don't intend to use voltage-drive for the LED, do you?
No, but what concerns me is that some Vactrols are clustered very close to 1.7V and others very close to 1.9V with nothing in between. It makes me suspicious that the LEDs may not be the same. From the opto resistor measurements I have made at 5mA the resistances are not that far apart so it may not be an issue but I am just suspicious by nature.

Cheers

Ian
 

abbey road d enfer

Well-known member
Staff member
GDIY Supporter
Moderator
Joined
Jan 22, 2008
Messages
14,702
Location
Marcelland
No, but what concerns me is that some Vactrols are clustered very close to 1.7V and others very close to 1.9V with nothing in between.
It just means they use different formulations.
It makes me suspicious that the LEDs may not be the same.
I think they are indeed different. As long as the performance template is satisfied, is it a problem?
From the opto resistor measurements I have made at 5mA the resistances are not that far apart so it may not be an issue
That's all that counts
but I am just suspicious by nature.
It may take a toll on the number of years you have to live... Relax.
 

Script

Well-known member
Joined
Nov 27, 2008
Messages
1,808
Location
Japan
Optocells are intended for mono- only unit(s)? For linked stereo unit ? Or intended for dual mono unit ?

Only in the latter case matching might be called for, and likely so if individual cells are too way-off But might try small value trimmers before LEDs. "What comp" used that, which later also inspired cell- matching of DAOC. Won't be perfect but good enough in many/most cases.
 

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,656
Location
Norfolk - UK
Optocells are intended for mono- only unit(s)? For linked stereo unit ? Or intended for dual mono unit ?

Only in the latter case matching might be called for, and likely so if individual cells are too way-off But might try small value trimmers before LEDs. "What comp" used that, which later also inspired cell- matching of DAOC. Won't be perfect but good enough in many/most cases.
Agree 100%. I was initially making measurements of opto resistance at a fixed current and out of curiosity decided to check LED forward voltage as well. I was hoping someone with much better semiconductor knowledge than I have could tell me if the observed spread was typical or not. The vendor has contacted Xvive on my behalf so hopefully they will have a definitive answer soon.

Cheers

Ian
 

abbey road d enfer

Well-known member
Staff member
GDIY Supporter
Moderator
Joined
Jan 22, 2008
Messages
14,702
Location
Marcelland
Optocells are intended for mono- only unit(s)? For linked stereo unit ? Or intended for dual mono unit ?

Only in the latter case matching might be called for, and likely so if individual cells are too way-off
I beg to differ. If you want any kind of repeatability, like maximum GR ot just having the correct markings on the front panel, you need to select optoresistive couplers, just like FET's in 1176's.
The designer's duty is to implement whatever adjustments are needed for the task. At least one for the ratio and one for the range. Even with these adjustments some matching is necessary.
Of course it's possible to make a one-off without any adjustments, but as you mentioned, don't expect a pair of them to behave correctly on a stereo signal, even with a common side-chain.
 
Top