Audio Optocouplers
learnabout-electronics.org
learnabout-electronics.org
(Unless you like the particular flavor of distortion these guys give. Then, by all means, help yourself!)
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.
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.
Diodes are incredibly nonlinear, that's the whole point of having 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.
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.
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.
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.
Looks like my favorite example has disappeared, but there are always these: http://www.audio-consulting.ch/?Parts:Woodlenses
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...
50 shades of quantum tunneling
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.
Thank God somebody is making these. Imagine if we had to wait almost twice as long!
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.
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.
(Note that this IS galvanic isolation--I assume you are talking about transformers, which is the other common way to galvanically isolating circuits.)
So at the same time, magnetically coupled.
Naturally subject to forces including back-EMF which are not shared by optics.
/s
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.
Page 9 if anyone is interested.
TL;DR to get good specs out of it is complex, just use ausio isolation transformer
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.
No.
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.
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.
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.
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.
https://www.audioholics.com/audio-amplifier/amp-myths-negati...
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
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 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.
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.
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.
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?
Careful, as Mr Carlson’s lab is addictive to watch :)
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.
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.