7 ms·

Audio Optocouplers

58 points by brudgers 4y ago

exmadscientist 4y ago
Be aware that these things have serious linearity (signal quality) issues, to the point where us "mere mortals" who design analog circuitry for T&M equipment try to stay away from them wherever possible. Audiophiles, of course, can hear the difference between copper, silver, gold, or platinum plating on the cable shield's drain wire in their neighbor's washing machine when he's on vacation in Hong Kong, so, you know, use with caution, you don't want to give them a heart attack or anything. (Unless you like the particular flavor of distortion these guys give. Then, by all means, help yourself!)
- dylan604 4y ago
  connect it to a foot pedal so a guitarist can use it to create a unique sound. it'll sell 10s of dollars!
  - xani_ 4y ago
    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
    - squarefoot 4y ago
      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.
      - fuzzfactor 4y ago
        >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.
        squarefoot 4y ago
        > 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.
- melony 4y ago
  Does the non-linearity come from the diode or does it come from the resistor?
  - deleted 4y ago
    [deleted]
  - klodolph 4y ago
    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.
    - melony 4y ago
      Isn't the diode linear only within a certain part of the VI graph?
      - jupp0r 4y ago
        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.
      - klodolph 4y ago
        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.
- GeneT45 4y ago
  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 http://www.audio-consulting.ch/?Parts:Woodlenses
  - the_third_wave 4y ago
    $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/ https://www.synergisticresearch.com/cables/srx-cables/srx-ac...
    - buescher 4y ago
      Before you bag on these guys, even though they deserve it, imagine the customer support issues...
    - elteto 4y ago
      > ...being obedient little atoms, they stay where they're told 50 shades of quantum tunneling
    - unfocused 4y ago
      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=34236938780811 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 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.
- jeffbee 4y ago
  Why would anyone choose these over galvanic isolation?
  - klodolph 4y ago
    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.)
    - jeffbee 4y ago
      You’re right that was lazy of me. But you got what I meant: transformers.
      - fuzzfactor 4y ago
        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.
        klodolph 4y ago
        just drive your optics hard enough, you'll see back-EMF /s
        fuzzfactor 4y ago
        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.
- fuckstick 4y ago
  I bet many of those audiophiles would either not tell the difference or love it if it was marketed accordingly.
- xani_ 4y ago
  https://www.vishay.com/docs/83708/appnote50.pdf 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
- voldacar 4y ago
  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.
  - daniel-cussen 4y ago
    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.
    - brokenmachine 4y ago
      >Airpods are the best headphone right now No.
      - daniel-cussen 4y ago
        Why not?
        voldacar 4y ago
        The best headphone right now is probably the utopia or x9000 in terms of raw resolution
- kazinator 4y ago
  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.
  - pclmulqdq 4y ago
    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.
  - voldacar 4y ago
    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.
MisterTea 4y ago
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).
- exmadscientist 4y ago
  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.
  - MisterTea 4y ago
    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.
  - buescher 4y ago
    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!
- xani_ 4y ago
  Did you put one of the diodes in the feedback loop to linearize them ?
  - amelius 4y ago
    Feedback is frowned upon in audiophile circles: https://www.audioholics.com/audio-amplifier/amp-myths-negative-feedback https://www.audioholics.com/audio-amplifier/amp-myths-negati...
aidos 4y ago
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.
- klodolph 4y ago
  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.
achr2 4y ago
Low cost ethernet transformers have a wider bandwidth and better linearity. And would work with similar topologies.
- jleahy 4y ago
  The core might saturate at these low frequencies?
- klodolph 4y ago
  "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.
  - achr2 4y ago
    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.
    - klodolph 4y ago
      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.
squarefoot 4y ago
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
jrockway 4y ago
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.
- mindslight 4y ago
  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.
  - jrockway 4y ago
    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!
    - pflanze 4y ago
      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.
      - mindslight 4y ago
CPLX 4y ago
For those that are into audio production you’ll recognize the concept of optical coupling as the basis of the legendary LA-2A compressor.
- buescher 4y ago
  The schematic is here: https://memory.loc.gov/master/mbrs/recording_preservation/manuals/Teletronix%20Model%20LA-2A%20Leveling%20Amplifier.pdf https://memory.loc.gov/master/mbrs/recording_preservation/ma...
- lebuffon 4y ago
  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.
  - CPLX 4y ago
    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.
buescher 4y ago
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.
twawaaay 4y ago
I solved a lot of audio problems in my complex setup (multiple inputs into multiple outputs) with a Toslink switch. Which is essentially a beefed up optocoupler...
- snvzz 4y ago
  Very, because digital.
jensenbox 4y ago
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?
- exmadscientist 4y ago
  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.
- unfocused 4y ago
  Have a watch of this video 15 min. Super informative on how AC DC signals work and rectifier circuits. https://youtu.be/qTb65aoYA_Y https://youtu.be/qTb65aoYA_Y Careful, as Mr Carlson’s lab is addictive to watch :)

58 points by brudgers 4y ago

Be aware that these things have serious linearity (signal quality) issues, to the point where us "mere mortals" who design analog circuitry for T&M equipment try to stay away from them wherever possible. Audiophiles, of course, can hear the difference between copper, silver, gold, or platinum plating on the cable shield's drain wire in their neighbor's washing machine when he's on vacation in Hong Kong, so, you know, use with caution, you don't want to give them a heart attack or anything. (Unless you like the particular flavor of distortion these guys give. Then, by all means, help yourself!)

dylan604 4y ago
connect it to a foot pedal so a guitarist can use it to create a unique sound. it'll sell 10s of dollars!
- xani_ 4y ago
  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
  - squarefoot 4y ago
    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.
    - fuzzfactor 4y ago
      >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.
      - squarefoot 4y ago
        > 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.
melony 4y ago
Does the non-linearity come from the diode or does it come from the resistor?
- deleted 4y ago
  [deleted]
- klodolph 4y ago
  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.
  - melony 4y ago
    Isn't the diode linear only within a certain part of the VI graph?
    - jupp0r 4y ago
      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.
    - klodolph 4y ago
      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.
GeneT45 4y ago
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 http://www.audio-consulting.ch/?Parts:Woodlenses
- the_third_wave 4y ago
  $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/ https://www.synergisticresearch.com/cables/srx-cables/srx-ac...
  - buescher 4y ago
    Before you bag on these guys, even though they deserve it, imagine the customer support issues...
  - elteto 4y ago
    > ...being obedient little atoms, they stay where they're told 50 shades of quantum tunneling
  - unfocused 4y ago
    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=34236938780811 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 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.
jeffbee 4y ago
Why would anyone choose these over galvanic isolation?
- klodolph 4y ago
  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.)
  - jeffbee 4y ago
    You’re right that was lazy of me. But you got what I meant: transformers.
    - fuzzfactor 4y ago
      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.
      - klodolph 4y ago
        just drive your optics hard enough, you'll see back-EMF /s
        fuzzfactor 4y ago
        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.
fuckstick 4y ago
I bet many of those audiophiles would either not tell the difference or love it if it was marketed accordingly.
xani_ 4y ago
https://www.vishay.com/docs/83708/appnote50.pdf 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
voldacar 4y ago
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.
- daniel-cussen 4y ago
  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.
  - brokenmachine 4y ago
    >Airpods are the best headphone right now No.
    - daniel-cussen 4y ago
      Why not?
      - voldacar 4y ago
        The best headphone right now is probably the utopia or x9000 in terms of raw resolution
kazinator 4y ago
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.
- pclmulqdq 4y ago
  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.
- voldacar 4y ago
  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.

MisterTea 4y ago

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).

exmadscientist 4y ago
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.
- MisterTea 4y ago
  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.
- buescher 4y ago
  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!
xani_ 4y ago
Did you put one of the diodes in the feedback loop to linearize them ?
- amelius 4y ago
  Feedback is frowned upon in audiophile circles: https://www.audioholics.com/audio-amplifier/amp-myths-negative-feedback https://www.audioholics.com/audio-amplifier/amp-myths-negati...

aidos 4y ago

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.

klodolph 4y ago
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.

achr2 4y ago

Low cost ethernet transformers have a wider bandwidth and better linearity. And would work with similar topologies.

jleahy 4y ago
The core might saturate at these low frequencies?
klodolph 4y ago
"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.
- achr2 4y ago
  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.
  - klodolph 4y ago
    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.

squarefoot 4y ago

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

jrockway 4y ago

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.

mindslight 4y ago
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.
- jrockway 4y ago
  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!
  - pflanze 4y ago
    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.
    - mindslight 4y ago

CPLX 4y ago

For those that are into audio production you’ll recognize the concept of optical coupling as the basis of the legendary LA-2A compressor.

buescher 4y ago
The schematic is here: https://memory.loc.gov/master/mbrs/recording_preservation/manuals/Teletronix%20Model%20LA-2A%20Leveling%20Amplifier.pdf https://memory.loc.gov/master/mbrs/recording_preservation/ma...
lebuffon 4y ago
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.
- CPLX 4y ago
  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.

buescher 4y ago

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.

twawaaay 4y ago

I solved a lot of audio problems in my complex setup (multiple inputs into multiple outputs) with a Toslink switch. Which is essentially a beefed up optocoupler...

snvzz 4y ago
Very, because digital.

jensenbox 4y ago

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?

exmadscientist 4y ago
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.
unfocused 4y ago
Have a watch of this video 15 min. Super informative on how AC DC signals work and rectifier circuits. https://youtu.be/qTb65aoYA_Y https://youtu.be/qTb65aoYA_Y Careful, as Mr Carlson’s lab is addictive to watch :)