Audio Optocouplers(learnabout-electronics.org)
learnabout-electronics.org
Audio Optocouplers
https://learnabout-electronics.org/Semiconductors/opto_53.php
85 comments
Your comment can only be truly appreciated by plumbing the bizarre depths of "high-end audio" where nitwits (errr... customers) will pay $700 for a 6' Kapton-insulated power cord for their stereo. You know, to plug into the wall where it connects to 100 ft of Romex that cost $0.20/ft...
Looks like my favorite example has disappeared, but there are always these: http://www.audio-consulting.ch/?Parts:Woodlenses
Looks like my favorite example has disappeared, but there are always these: http://www.audio-consulting.ch/?Parts:Woodlenses
What I don't get about this is that marketers keep getting away with pushing this BS on the audiofool public.
There is a core group of audiophile/EEs who design DACs, amps and the like and who do know what matters for sound quality, and there's a whole pile of marketers who try to jump on the train with gold-plated power cables and (apparently) expensive chunks of wood. The engineers don't seem to care to call out the marketers on their BS. Maybe they just aren't effective at it.
As a result, the public can't really tell the difference between true and false things, like how gold-plated headphone connectors are more conductive and durable than the cheap version (and thus sound better), but gold plated power cables have no effect on sound quality. If they did, there might be a lot more audiophiles since there is some semblance of authority about what is worth paying for. The engineers are sabotaging their market by refusing to educate customers.
There is a core group of audiophile/EEs who design DACs, amps and the like and who do know what matters for sound quality, and there's a whole pile of marketers who try to jump on the train with gold-plated power cables and (apparently) expensive chunks of wood. The engineers don't seem to care to call out the marketers on their BS. Maybe they just aren't effective at it.
As a result, the public can't really tell the difference between true and false things, like how gold-plated headphone connectors are more conductive and durable than the cheap version (and thus sound better), but gold plated power cables have no effect on sound quality. If they did, there might be a lot more audiophiles since there is some semblance of authority about what is worth paying for. The engineers are sabotaging their market by refusing to educate customers.
There's stupid shit and it involves scams, like going to a record store and they say "hey maybe you're the chosen one" play a track then switch gear and say "listen to it again" and play a different track pretending to be the first, and bam, audiophile.
Then there's the blind. One of my ancestors was a blind Spanish classical guitarist, played in concerts often. So for them? They can tell you the brand of headphones you're listening to from the other side of the room. And that's nothing. They also think faster, listen to sound at a much much faster rate than ordinary speech. Like 4x? Something. Sky's the limit. And when they speak to each other they speak much faster more like the speech synthesizer.
Then there's the blind. One of my ancestors was a blind Spanish classical guitarist, played in concerts often. So for them? They can tell you the brand of headphones you're listening to from the other side of the room. And that's nothing. They also think faster, listen to sound at a much much faster rate than ordinary speech. Like 4x? Something. Sky's the limit. And when they speak to each other they speak much faster more like the speech synthesizer.
$700, where do you buy your cables, at McDonalds?
No, if you want to have really clear audio you'd better get one of those Synergistic Research cables [1]. For a mere $10.000,- starting price (6 ft, add $1000/ft if you want a longer cable) it will be as if the musicians are sitting on your table, eating your cookies and petting your dog. It's the Quantum tunneling which does the trick, see? They kick the atoms into the right shape using a Tesla coil and, being obedient little atoms, they stay where they're told. Or something.
[1] https://www.synergisticresearch.com/cables/srx-cables/srx-ac...
No, if you want to have really clear audio you'd better get one of those Synergistic Research cables [1]. For a mere $10.000,- starting price (6 ft, add $1000/ft if you want a longer cable) it will be as if the musicians are sitting on your table, eating your cookies and petting your dog. It's the Quantum tunneling which does the trick, see? They kick the atoms into the right shape using a Tesla coil and, being obedient little atoms, they stay where they're told. Or something.
[1] https://www.synergisticresearch.com/cables/srx-cables/srx-ac...
C'mon! Everybody knows that the Nordost Valhalla 2 Power Cord is far superior than the SRX. It's also only $10,079.99 CAD for 6ft, so it will be less than yours since yours is in USD, saving you money to to buy fridge magnets which will help dampen the magnetic field from any orphan atoms that may leak through.
Also, from the manufacturer's brochure: Unlike conventional power cables, which have propagation speeds that are less than 50% the speed of light, the Valhalla 2 Reference Power Cord has a speed of 91% the speed of light.
[1] https://audiofi.ca/products/valhalla-2-power-cord?variant=34...
EDIT: On a more serious note, check out https://www.audiosciencereview.com/forum/index.php for real testing, where the dollar store speaker cable performed (surprise!) as well as the fancy cables. The fancy cable company was not happy.
Also, from the manufacturer's brochure: Unlike conventional power cables, which have propagation speeds that are less than 50% the speed of light, the Valhalla 2 Reference Power Cord has a speed of 91% the speed of light.
[1] https://audiofi.ca/products/valhalla-2-power-cord?variant=34...
EDIT: On a more serious note, check out https://www.audiosciencereview.com/forum/index.php for real testing, where the dollar store speaker cable performed (surprise!) as well as the fancy cables. The fancy cable company was not happy.
This discussion has been going on for a long time. Power cables are not going to fix anything. Speaker cables, I have my doubts. I use the cheap stuff, but would go for all copper if I were splurging. On the other hand, I have bought about-dollar-store-cheap interconnects with problems, so I go for the fancy Amazon Basics level stuff myself. I get the guys that buy aesthetically pleasing cables, but that's a different story. Here's Bob Pease on the subject(s):
https://www.pearl-hifi.com/06_Lit_Archive/02_PEARL_Arch/Vol_...
> Unlike conventional power cables, which have propagation speeds that are less than 50% the speed of light, the Valhalla 2 Reference Power Cord has a speed of 91% the speed of light.
Thank God somebody is making these. Imagine if we had to wait almost twice as long!
Thank God somebody is making these. Imagine if we had to wait almost twice as long!
Before you bag on these guys, even though they deserve it, imagine the customer support issues...
> ...being obedient little atoms, they stay where they're told
50 shades of quantum tunneling
50 shades of quantum tunneling
That quantum tunneling is done by hand in California, using six-zeros volts of electricity. Pretty impressive.
Forget the 100ft of in house cable. What about the miles and miles of outdoor power lines…
Hard to beat that corroded aluminium sound!
I read a story about hifi enthusiasts in japan who ended up getting dedicated external powerpole transformers installed for supposed cleaner power and as a bit of a status symbol.
Speaking of audiofools, look no further than the Machina Dynamica store (https://www.machinadynamica.com/) that features magic rocks, CD stickers, and other items you can add to your system to improve sound. Literally the whole site reads like it's satire - but apparently people actually buy their stuff.
The magic rocks and other physical devices are old hat. For $60, you can just call Machina Dynamica's phone number, and they'll play a 20-second "series of mechanical pulses" which remotely transforms your phone onto exotic matter, thereby severing its quantum connection to the "cell phone information field" that would otherwise be degrading the quality of every audio/video device in your home.
http://www.machinadynamica.com/machina60.htm
http://www.machinadynamica.com/machina60.htm
My favorite example is the Shakti stone, no longer on Stereophile's recommended accessories list. Who knows if they work? I have done enough EMI mitigation to think "not damned likely" but I have also done enough EMI mitigation (read the patent first, and the testimonials from people who should know better) that I wouldn't bet a paycheck on it.
Just like everywhere else, silliness in the audio world is Pareto distributed.
As someone who loves good sound reproduction, it's tiresome to have people endlessly start talking about magic rocks or whatever whenever the topic of audio quality or audio electronics is brought up online. What's sad to me is that a lot of this cynicism seems to come from people who haven't even heard a really good pair of speakers or headphones, and it drives people away from having potentially beautiful experiences. Go visit your local high end audio shop and ask for a demo. They will probably be glad to have you. Listnening to well-recorded music through great transducers and electronics in a well-treated room is a mind blowing experience if you haven't tried it.
As someone who loves good sound reproduction, it's tiresome to have people endlessly start talking about magic rocks or whatever whenever the topic of audio quality or audio electronics is brought up online. What's sad to me is that a lot of this cynicism seems to come from people who haven't even heard a really good pair of speakers or headphones, and it drives people away from having potentially beautiful experiences. Go visit your local high end audio shop and ask for a demo. They will probably be glad to have you. Listnening to well-recorded music through great transducers and electronics in a well-treated room is a mind blowing experience if you haven't tried it.
Yeah I don't actually value happiness but insofar as I do it simply means headphones. Good headphones. Audio quality yeah, but also unique way it plays songs, listen to everything all over again. And convenience, so for instance Airpods are the best headphone right now because it works well with masks, you don't have to put one over the other, meaning removing one requires removing the other. The convenience, the battery life, all that. Audio isn't just what you hear when everything's set up, it's also hearing sound when other systems would play nothing.
>Airpods are the best headphone right now
No.
No.
Why not?
The best headphone right now is probably the utopia or x9000 in terms of raw resolution
If it's nonlinear, the audiophile is guaranteed to relish the warm tone.
The definition of an audiophile is: someone who listens to the speakers (or the equipment, in general) rather than the music. Without distortion, there is nothing for the audiophile to listen to.
The definition of an audiophile is: someone who listens to the speakers (or the equipment, in general) rather than the music. Without distortion, there is nothing for the audiophile to listen to.
This hasn't been my experience with many audiophiles. There are many who are obsessed with the "transparency" of their setup, and I have met more of those than people obsessed with "tube sound" or other distortions.
This is just ignorant. Plenty of audiophiles (including myself) go after gear that's as neutral and transparent as possible. Also warmth and distortion aren't the same thing.
connect it to a foot pedal so a guitarist can use it to create a unique sound. it'll sell 10s of dollars!
Unironically diode-to-photoresistor optocouplers are used in some compressors and filters to get that soft analoguey sound (as they are plain slow to react to signal). Which is kinda a supply problem as material they were made with was banned for toxicity
True. LDRs (photoresistors) are however still very easy to find on the usual online suppliers (Ebay, Aliexpress etc.) although they're banned in some areas for containing cadmium. I've used them successfully in LED+LDR arrangements to emulate Vactrols in vintage-style audio compressor circuits. To replicate the vintage compressor slow attack, in theory one should use a filament lamp+LDR pair so that the lamp slower attack and very slow decay, compared to a LED, would give that particular curve. However this is something that can be easily replicated using a RC network within the circuit that drives the LED.
>diode-to-photoresistor optocouplers
The crude (but wonderful sounding) type like they have in vintage Fender tube amps are used to effect the signal, not pass the entire signal.
Can't read the article but I assume these Audio Optocouplers are intended to pass the entire signal in an acceptable way.
I don't think they would be very good for T & M use either unless you were desperate for isolation.
I found great use for the regular 4-legged kind of precision non-audio optos, to isolate the physical relay logic from the audio power supply for much lower noise floor under high-gain channel-switching applications.
The crude (but wonderful sounding) type like they have in vintage Fender tube amps are used to effect the signal, not pass the entire signal.
Can't read the article but I assume these Audio Optocouplers are intended to pass the entire signal in an acceptable way.
I don't think they would be very good for T & M use either unless you were desperate for isolation.
I found great use for the regular 4-legged kind of precision non-audio optos, to isolate the physical relay logic from the audio power supply for much lower noise floor under high-gain channel-switching applications.
> The crude (but wonderful sounding) type like they have in vintage Fender tube amps are used to effect the signal, not pass the entire signal.
Yes, I was referring to the use as variable resistors in compressor circuits; the sound wasn't affected at all but the slow attack-release induced to the dynamics contributed to that particular character in vintage guitar amplifiers.
Yes, I was referring to the use as variable resistors in compressor circuits; the sound wasn't affected at all but the slow attack-release induced to the dynamics contributed to that particular character in vintage guitar amplifiers.
https://www.vishay.com/docs/83708/appnote50.pdf
Page 9 if anyone is interested.
TL;DR to get good specs out of it is complex, just use ausio isolation transformer
Page 9 if anyone is interested.
TL;DR to get good specs out of it is complex, just use ausio isolation transformer
Does the non-linearity come from the diode or does it come from the resistor?
[deleted]
Resistors are generally very linear. They're put in the same category as transformers, capacitors, and inductors, where we just ignore the non-linearities--they're usually too small to measure, although reverse-biased electrolytic capacitors are definitely nonlinear and I've heard you can be affected by nonlinearity on carbon-composition resistors if you put enough voltage across them--like, 100V--don't know if it's true, just "heard it somewhere".
Diodes are incredibly nonlinear, that's the whole point of having diodes.
Diodes are incredibly nonlinear, that's the whole point of having diodes.
Some dude did a whole series of capacitor linearity articles in Electronics World a couple of decades ago, with measurements. I should revisit them, but I don't have all the issues... but the internet gives:
https://linearaudio.nl/cyril-batemans-capacitor-sound-articl...
Isn't the diode linear only within a certain part of the VI graph?
It's not really linear anywhere, except in the sense that it's got a smooth VI graph, so you can pick a point on the curve and draw a tangent line if you want. That's not really linear, unless you have small enough signals or bad enough oscilloscopes.
It's much closer to exponential, which is Shockley diode equation / "diode law" which is the simplest model you would use besides the "diode is a one-way switch with a voltage threshold" model.
The diode law is I = Is[ exp(VD/nVT) - 1 ].
There are more sophisticated models of the diode that use multiple exponentials. Remember that these are all just approximations of reality based on some simplifying assumptions, the only real question is "how much do you want to simplify", and linear models are very rarely useful for modeling diodes.
It's much closer to exponential, which is Shockley diode equation / "diode law" which is the simplest model you would use besides the "diode is a one-way switch with a voltage threshold" model.
The diode law is I = Is[ exp(VD/nVT) - 1 ].
There are more sophisticated models of the diode that use multiple exponentials. Remember that these are all just approximations of reality based on some simplifying assumptions, the only real question is "how much do you want to simplify", and linear models are very rarely useful for modeling diodes.
This is one thing that's always annoyed me about reading EE books - just tell me the equation and I'll approximate it (thank you), don't tell me a million approximations before the actual behaviour.
You're asking for "the equation", but "the equation" does not exist. There are always multiple approximations, and the only ground truth is experiments (with messy data that does not exactly fit the equations) and the underlying quantum mechanics (which is difficult to simulate).
If you want something super accurate you can end up running a solid state physics simulation.
If you want to model a circuit in SPICE, you get to pick from like a dozen different models for transistors, depending on what you care about--including execution time for your simulation!
If you're designing a circuit, it might be easier to think of a transistor as an infinite gain transconductance amplifier, or something equally absurd--and yet useful. If you're designing for RF, then you have to abandon the lumped component model--there is no longer any such thing as a "wire", everything is instead connected by miniature antennas. Trying to teach this to freshmen EE students is insanity.
The problem here is that actual insight into how something works is not something that you should conflate with accuracy. The model you choose is something that mediates your understanding of reality. By choosing the right simplifying assumptions, you get something that provides you with the right balance of insight and accuracy. Over the years, people have come up with many models at different points on that tradeoff between insight and accuracy, which allow you to understand circuits and components in different ways. It would be wise to "stand on these shoulders of giants", so to speak, and use these high-value models that balance insight with accuracy, unless you are really interested in studying solid-state-physics in which case, by all means, go as far into the deep end as you want.
We still teach freshmen physics students that momentum is mass times velocity, or something like that, for the same reason. It doesn't make sense to explode someone's head with quantum physics and general relativity and then try to introduce Newtonian mechanics as a limiting case. Precious few students would survive.
If you want something super accurate you can end up running a solid state physics simulation.
If you want to model a circuit in SPICE, you get to pick from like a dozen different models for transistors, depending on what you care about--including execution time for your simulation!
If you're designing a circuit, it might be easier to think of a transistor as an infinite gain transconductance amplifier, or something equally absurd--and yet useful. If you're designing for RF, then you have to abandon the lumped component model--there is no longer any such thing as a "wire", everything is instead connected by miniature antennas. Trying to teach this to freshmen EE students is insanity.
The problem here is that actual insight into how something works is not something that you should conflate with accuracy. The model you choose is something that mediates your understanding of reality. By choosing the right simplifying assumptions, you get something that provides you with the right balance of insight and accuracy. Over the years, people have come up with many models at different points on that tradeoff between insight and accuracy, which allow you to understand circuits and components in different ways. It would be wise to "stand on these shoulders of giants", so to speak, and use these high-value models that balance insight with accuracy, unless you are really interested in studying solid-state-physics in which case, by all means, go as far into the deep end as you want.
We still teach freshmen physics students that momentum is mass times velocity, or something like that, for the same reason. It doesn't make sense to explode someone's head with quantum physics and general relativity and then try to introduce Newtonian mechanics as a limiting case. Precious few students would survive.
We do not however teach general relativity linearization-first and only then the full equations.
My point is that for the purposes of the book the equation does "exist", it's just introduced in an extremely meandering-y way. Giving different approximate circuits is fine afterwards but I've spent years and years honing my skills in other quantitative disciplines so I'd prefer to just be given detail in a practical way rather than have detail broken down into practical chunks that loses the essence of the model.
More subtly the idea of a limiting case doesn't always make any obvious sense in electronics unless you speak in unbelievably broad terms that only a physicist would care about (i.e. intuitively you can handwave about some quantity in a circuit relative to the speed of light but you ain't gonna be able to write down an equation and literally take a limit), abstractions/rules-of-thumbs in electronics are often very clever because of that.
I had a lot of fun playing around with RF going through metallic clothes (fencing lames) since basically no amount of theory would really help you so you just have to really stare at the VNA output.
My point is that for the purposes of the book the equation does "exist", it's just introduced in an extremely meandering-y way. Giving different approximate circuits is fine afterwards but I've spent years and years honing my skills in other quantitative disciplines so I'd prefer to just be given detail in a practical way rather than have detail broken down into practical chunks that loses the essence of the model.
More subtly the idea of a limiting case doesn't always make any obvious sense in electronics unless you speak in unbelievably broad terms that only a physicist would care about (i.e. intuitively you can handwave about some quantity in a circuit relative to the speed of light but you ain't gonna be able to write down an equation and literally take a limit), abstractions/rules-of-thumbs in electronics are often very clever because of that.
I had a lot of fun playing around with RF going through metallic clothes (fencing lames) since basically no amount of theory would really help you so you just have to really stare at the VNA output.
That's the difference between science and engineering. Engineering only needs to be good enough to achieve the desired results. If a simplified model gets you there then something more accurate isn't worth the bother.
> [...] I'd prefer to just be given detail in a practical way rather than have detail broken down into practical chunks that loses the essence of the model.
I am not trying to come across overly critical here, but I think this is a flawed approach to learning.
My professional experience with EE is from working on circuit simulators. As in, I was a software engineer working on a SPICE simulator tool (it was actually mixed-signal, and some other stuff, SPICE was just part of it). There are a lot of transistor models out there. There's not some ideal model out there which is the best model and the other models are just simplifications of it. I think you may be underestimating how rich the field of modeling is, underestimating how complicated the more accurate models are, and overestimating how much insight you would get by playing around with the more sophisticated / accurate equations.
One problem with these more complicated models is that you have so many parameters and the parameters have effects that typically vary by orders of magnitude depending on the regime you are interested in. Another problem is that the complicated models may require the use of mathematical techniques that I simply don't have the time to deal with. Whereas if I look at the humble Shockley diode equation, I can instantly understand a couple good approximations about diodes:
- The current always flows,
- Every diode is a temperature sensor.
These insights are (for me) easy to figure out from the Shockley diode equation, and that makes the Shockley diode equation extremely valuable.
However, if I'm trying to understand the frequency response of a particular diode, this model doesn't have it, and I might switch from ODEs to PDEs. The diode has an electrical field which varies from one end of the diode to the other, and it has two different charge carriers, which are generated and recombine at different rates at different positions in the diode, have various drift currents, different amounts of momentum, etc. This provides the additional accuracy. Given this more accurate model,
- I'm not sure that I would be able to derive the Shockley equation at all, certainly not in a reasonable time frame, except for the fact that I already know the Shockley equation and could "work in both directions".
- I'm not sure I could get the simpler insights out of this more complicated model, at least in a reasonable time frame.
I'm the kind of student who never memorized formulas and always derived things from first principles on tests. It took me a bit longer, but I was happy to do it this way. It works well enough in some fields--very well in mathematics and statistics, somewhat well in physics, less well in electrical engineering. That's why I think it's a flawed approach to learning--it's an approach which I've personally relied too much upon, and met its limitations.
In order to get any work done at all when designing circuits or doing practical EE work, I must have multiple models in my toolbox, with varying levels of complexity.
I am not trying to come across overly critical here, but I think this is a flawed approach to learning.
My professional experience with EE is from working on circuit simulators. As in, I was a software engineer working on a SPICE simulator tool (it was actually mixed-signal, and some other stuff, SPICE was just part of it). There are a lot of transistor models out there. There's not some ideal model out there which is the best model and the other models are just simplifications of it. I think you may be underestimating how rich the field of modeling is, underestimating how complicated the more accurate models are, and overestimating how much insight you would get by playing around with the more sophisticated / accurate equations.
One problem with these more complicated models is that you have so many parameters and the parameters have effects that typically vary by orders of magnitude depending on the regime you are interested in. Another problem is that the complicated models may require the use of mathematical techniques that I simply don't have the time to deal with. Whereas if I look at the humble Shockley diode equation, I can instantly understand a couple good approximations about diodes:
- The current always flows,
- Every diode is a temperature sensor.
These insights are (for me) easy to figure out from the Shockley diode equation, and that makes the Shockley diode equation extremely valuable.
However, if I'm trying to understand the frequency response of a particular diode, this model doesn't have it, and I might switch from ODEs to PDEs. The diode has an electrical field which varies from one end of the diode to the other, and it has two different charge carriers, which are generated and recombine at different rates at different positions in the diode, have various drift currents, different amounts of momentum, etc. This provides the additional accuracy. Given this more accurate model,
- I'm not sure that I would be able to derive the Shockley equation at all, certainly not in a reasonable time frame, except for the fact that I already know the Shockley equation and could "work in both directions".
- I'm not sure I could get the simpler insights out of this more complicated model, at least in a reasonable time frame.
I'm the kind of student who never memorized formulas and always derived things from first principles on tests. It took me a bit longer, but I was happy to do it this way. It works well enough in some fields--very well in mathematics and statistics, somewhat well in physics, less well in electrical engineering. That's why I think it's a flawed approach to learning--it's an approach which I've personally relied too much upon, and met its limitations.
In order to get any work done at all when designing circuits or doing practical EE work, I must have multiple models in my toolbox, with varying levels of complexity.
That's something that mechanics books do a lot better than EE books, as far as I've seen.
Also, this is why you (can) use diodes in log amps and ring multipliers/mixers.
No, it's exponential all around. For any infinitesimal small delta V you can assume it to be almost linear. This works for amplifying really small signals.
Why would anyone choose these over galvanic isolation?
It's way cheaper. Like, it's not even close.
(Note that this IS galvanic isolation--I assume you are talking about transformers, which is the other common way to galvanically isolating circuits.)
(Note that this IS galvanic isolation--I assume you are talking about transformers, which is the other common way to galvanically isolating circuits.)
You’re right that was lazy of me. But you got what I meant: transformers.
Magnetic isolation more specifically, when you think about it.
So at the same time, magnetically coupled.
Naturally subject to forces including back-EMF which are not shared by optics.
So at the same time, magnetically coupled.
Naturally subject to forces including back-EMF which are not shared by optics.
just drive your optics hard enough, you'll see back-EMF
/s
/s
I've driven non-photo resistors to the point you could see the glowing in time to the music ;-)
And smell the smoke.
Now with a 1500W space heater as a dummy load on a 1000W amp, you hear a little music come out of the heating elements without any speakers.
And smell the smoke.
Now with a 1500W space heater as a dummy load on a 1000W amp, you hear a little music come out of the heating elements without any speakers.
I bet many of those audiophiles would either not tell the difference or love it if it was marketed accordingly.
Optocouplers are neat. I few months ago, it was the middle of the night and I was thinking about how to add AC frequency monitoring to my GPS clock project. (Any frequency source is fun; I have two GPSes, a DS3231, a WWVB module, etc.) I didn't have any optocouplers, but I heard that LEDs work as photodiodes. Indeed, I found some random LEDs, connected one to mains with a large resistor, and pointed it at another LED. A 60Hz voltage appeared on the leads of the second LED. I then went to sleep instead of finding an ADC and writing the frequency sampling code... and so the thing never made it into production. But, neat surprise. If you want a quick and dirty optoisolator, you only need one type of component: the humble LED.
If you do get back to this project, you'd be better off with an X rated capacitor instead of a resistor. Lower power consumption, and it's explicitly rated to be across the line. I'd add a small fast acting fuse, as well.
This was a 3mA LED, so the inefficiency of a resistor didn't matter that much. I think I used a 50k or 100k ohm resistor. Didn't need to get to full brightness either!
At 120 V that's 0.36 W (if using both halves of the AC wave), if you use that 10 years non-stop you'll burn 31 KWh, a value of 5-20$ or so, thus if you were to produce many of these devices it would be worthwhile to lower :). But sure, for a one-off it won't matter.
OTOH I'm wondering how you didn't break the LED during the reverse cycles of the AC wave, if you didn't use either a high-voltage diode in sequence or some random diode or second LED in reverse direction in parallel to the first one to bypass the other half of the wave.
OTOH I'm wondering how you didn't break the LED during the reverse cycles of the AC wave, if you didn't use either a high-voltage diode in sequence or some random diode or second LED in reverse direction in parallel to the first one to bypass the other half of the wave.
Good point about needing to plan for both halves of the wave. That's especially true for my capacitor suggestion. Last time I designed something (trickle supply) with line rated capacitors, the DC component was a zener which has that built in.
My line capacitor suggestion was really just to get one started thinking about an actual circuit design for longer term. A 1/4 W resistor in serious with line voltage works fine on the test bench, but for longer term non-attended usage I would think about the various ways things could go wrong. And if you're going to spec a special resistor, then you might as well spec a special capacitor instead.
If I had to guess about why the LED wasn't destroyed, it's because the reverse breakdown voltage is low enough that significant heat does not build up in the LED. A reverse avalanche isn't necessarily destructive.
My line capacitor suggestion was really just to get one started thinking about an actual circuit design for longer term. A 1/4 W resistor in serious with line voltage works fine on the test bench, but for longer term non-attended usage I would think about the various ways things could go wrong. And if you're going to spec a special resistor, then you might as well spec a special capacitor instead.
If I had to guess about why the LED wasn't destroyed, it's because the reverse breakdown voltage is low enough that significant heat does not build up in the LED. A reverse avalanche isn't necessarily destructive.
If you need to electrically isolate an audio signal path, decent audio transformers aren't that expensive these days. A Triad Magnetics TY-250P is less than €6 at Mouser in single quantity, and is for sure a lot more linear than most optocouplers.
https://eu.mouser.com/datasheet/2/410/TY_250P-1892894.pdf
https://eu.mouser.com/datasheet/2/410/TY_250P-1892894.pdf
I've used the IL300's to interface signals in a legacy machine to a PLC and found they were not very linear. Don't see how these 4N25's will be any better. Wound up using texas instruments/burr brown isolation amplifiers instead (ISO122 or something).
Those are probably great if you can afford them. I've never had the budget for them in a production design, so haven't played with them much. Standard practice these days is just to toss a full ADC on the other side of the barrier and then isolate the SPI bus (or what-have-you). A few ADCs have the isolation built in, but for others there's stuff like TI's ISOW7841, which have 4 isolated digital lines plus isolated power in one package. It's all kind of expensive when added up, but it's cheaper than the old style analog isolation amplifiers, and you'll usually get more than one ADC channel once everything's together, so you win as soon as you want two signals to cross the barrier.
This was 10+ years ago and was a smaller internal project for two older machines so we didn't care they were $20 or $30 each.
And the isolated digital trick is used in the new industrial isolators. The neat part is since there's a micro in them they add in scaling and conditioning options which is nice.
And the isolated digital trick is used in the new industrial isolators. The neat part is since there's a micro in them they add in scaling and conditioning options which is nice.
This is why I'm glad I don't do automation one-offs and remind myself to have respect for those that do. It's such a different solution space!
Did you put one of the diodes in the feedback loop to linearize them ?
Yes but there were still linearity issues. The senior engineer played with it for a bit until he said screw it, spend the money and be done. Project was small enough to justify the cost.
Do you remember numbers ? I'd guess somewhere in 0.5-1% THD range for simple single opamp servo ? I was kinda mildly interested into doing it for sensors altho just microprocessor blasting serial via optocoupler onto other side seems like easier solution...
Their application note (page 9) details circuits most audio people would just look at it and go "screw it, i will just buy audio transformer like rest of us"
https://www.vishay.com/docs/83708/appnote50.pdf
I don't doubt they achieved the claimed values but the circuit to do it had 4 precision opamps (bipolar one have 7) and a bunch of other components so I'm not surprised he didn't want to bother
Their application note (page 9) details circuits most audio people would just look at it and go "screw it, i will just buy audio transformer like rest of us"
https://www.vishay.com/docs/83708/appnote50.pdf
I don't doubt they achieved the claimed values but the circuit to do it had 4 precision opamps (bipolar one have 7) and a bunch of other components so I'm not surprised he didn't want to bother
Sorry, cant remember specifics. But if I were doing this again, today, I'd use an isolated serial ADC. I had a lot of fun with analog stuff but fixing signal issues in code is easier than solder.
Feedback is frowned upon in audiophile circles:
https://www.audioholics.com/audio-amplifier/amp-myths-negati...
https://www.audioholics.com/audio-amplifier/amp-myths-negati...
I am not an audio expert, and those circuits, 324 op-amp and all, hurt my eyes. That said, I didn't look close, and they might be fine for what you might call "utility audio".
The IL300 at least has defined linearity specs. If you do audio design you'll be better qualified than me to comment on them. But I can say: remember, too, if you're using these that they're basically current devices, the transfer ratio across the gap is going to be all over the map in production, feedback is another design challenge, and the saturation voltage will be high, all over the map, and basically the point where more light will not turn on the transistor any more.
If it's a hobby project, have fun, that's the point.
The IL300 at least has defined linearity specs. If you do audio design you'll be better qualified than me to comment on them. But I can say: remember, too, if you're using these that they're basically current devices, the transfer ratio across the gap is going to be all over the map in production, feedback is another design challenge, and the saturation voltage will be high, all over the map, and basically the point where more light will not turn on the transistor any more.
If it's a hobby project, have fun, that's the point.
I had a brief foray into electronics a few years ago hacking about with making a really crummy arduino synth. Part of that involved wiring it up to the midi output of a controller.
The concept of an optocoupler is just beautiful - isolate the circuits from each other by transferring your signal using light!
Looking at the diagrams here of how to increase the bandwidth through the device, electronics is all still total voodoo to me.
The concept of an optocoupler is just beautiful - isolate the circuits from each other by transferring your signal using light!
Looking at the diagrams here of how to increase the bandwidth through the device, electronics is all still total voodoo to me.
The second circuit is actually really boring once you recognize the parts. From left-to-right, it's:
1. A voltage to current converter
2. An optocoupler
3. A buffer
4. An amplifier
Stage #1 drives the optocoupler, since current is what gets turned into light inside the optocoupler.
The output is high-impedance, so you add a buffer, which is #3.
The output has a low-level, so you amplify it, which is #4.
If you work through a chapter of an EE book that explains op amps, and you're not afraid of algebra, you'll find this stuff becomes approachable very quickly. Designing circuits like this is a bit more challenging, but reading them is very approachable.
1. A voltage to current converter
2. An optocoupler
3. A buffer
4. An amplifier
Stage #1 drives the optocoupler, since current is what gets turned into light inside the optocoupler.
The output is high-impedance, so you add a buffer, which is #3.
The output has a low-level, so you amplify it, which is #4.
If you work through a chapter of an EE book that explains op amps, and you're not afraid of algebra, you'll find this stuff becomes approachable very quickly. Designing circuits like this is a bit more challenging, but reading them is very approachable.
For those that are into audio production you’ll recognize the concept of optical coupling as the basis of the legendary LA-2A compressor.
The schematic is here:
https://memory.loc.gov/master/mbrs/recording_preservation/ma...
The LA-2A is great compressor. To be clear it uses a different application of "optical coupling" in that Audio is not passing through the optical connection.
The light source is driven by a DC amplifier that generates a control voltage derived from the audio signal. The light shines onto a photo-resistor that is used as the shunt component of an audio pad. (attenuator)
As the light intensity increases the pad reduces the signal level at the pad creating an audio compressor.
The light source is driven by a DC amplifier that generates a control voltage derived from the audio signal. The light shines onto a photo-resistor that is used as the shunt component of an audio pad. (attenuator)
As the light intensity increases the pad reduces the signal level at the pad creating an audio compressor.
Yes this is of course correct and a worthwhile point to make. The fidelity of an actual optical transfer function will never be even close enough to the level needed for the transmission of actual high quality audio.
Could someone explain why nearly all amplifiers I see only amplify one half of the wave? I am seeing these optocouplers as only being able to amplify the positive side of the cycle and ignoring the negative.
In my mind I see the sound pressure as a positive and a negative where each side could be very different but ultimately adding up to zero over time.
Is it just that if you make a positive pressure wave the negative is right after and does not matter?
Class A amplifiers seem to take both sides into account. I am expecting to see some sort of H-Bridge configuration but never really see it. The most I see are positive and negative rails.
What am I missing here?
In my mind I see the sound pressure as a positive and a negative where each side could be very different but ultimately adding up to zero over time.
Is it just that if you make a positive pressure wave the negative is right after and does not matter?
Class A amplifiers seem to take both sides into account. I am expecting to see some sort of H-Bridge configuration but never really see it. The most I see are positive and negative rails.
What am I missing here?
I think the search term you're looking for is "AC coupling". I have mostly done instrumentation work, which is usually DC-coupled, needing bipolar supplies to get the job done but doesn't have a low-frequency cutoff from the coupling capacitor.
Have a watch of this video 15 min. Super informative on how AC DC signals work and rectifier circuits.
https://youtu.be/qTb65aoYA_Y
Careful, as Mr Carlson’s lab is addictive to watch :)
https://youtu.be/qTb65aoYA_Y
Careful, as Mr Carlson’s lab is addictive to watch :)
Low cost ethernet transformers have a wider bandwidth and better linearity. And would work with similar topologies.
The core might saturate at these low frequencies?
"Wider bandwidth" is not so useful if the wide bandwidth does not include the frequencies you care about. Generally speaking, the higher the frequency, the smaller the transformer. Ethernet deals with very high frequencies, so they can make nice, cheap transformers.
Try putting audio through an ethernet transformer and see how much comes out the other side... I bet it won't be much, and you'll get extreme distortion unless your signal levels are very low.
Try putting audio through an ethernet transformer and see how much comes out the other side... I bet it won't be much, and you'll get extreme distortion unless your signal levels are very low.
Thank you for correcting me. I misspoke and said ethernet when I was thinking modem. Many are rated from ~300Hz. And I did assume low signal levels in a similar gain setup from the article.
I think modem transformers might have a similar problem of limited bandwidth--they may be rated from 300 Hz, but they are also rated to 3.4 kHz or something similar. Modems were mass-manufactured, and transformers tend to be expensive, so you would expect any expensive part in a mass-manufactured product to be engineered to within a hair's breadth of the specification for modems, which have something like 300 Hz - 3.4 kHz frequency range.
On the low end, you have core saturation. On the high end, you have parasitic inductance and capacitance, as well as loss from hysteresis and eddy currents. Solving these problems basically means making the transformer larger and more expensive.
I did a quick search on Mouser, and found wideband (20 Hz - 20 kHz) audio transformers at around $6 in small quantities. Let's say that you get it for $3 in bulk. At that point, you're adding something like $20 or $30 to the retail cost of whatever it is you're selling.
If you're okay with the telephone-quality of the simple modem transformers, then you might as well use the optoisolator--neither option sounds good, but the optoisolator is cheaper. You know, as long as you have a power supply on both sides--which is not a given.
On the low end, you have core saturation. On the high end, you have parasitic inductance and capacitance, as well as loss from hysteresis and eddy currents. Solving these problems basically means making the transformer larger and more expensive.
I did a quick search on Mouser, and found wideband (20 Hz - 20 kHz) audio transformers at around $6 in small quantities. Let's say that you get it for $3 in bulk. At that point, you're adding something like $20 or $30 to the retail cost of whatever it is you're selling.
If you're okay with the telephone-quality of the simple modem transformers, then you might as well use the optoisolator--neither option sounds good, but the optoisolator is cheaper. You know, as long as you have a power supply on both sides--which is not a given.
(Unless you like the particular flavor of distortion these guys give. Then, by all means, help yourself!)