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Comment by exmadscientist | Hacker News Reader

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!)

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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

$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...

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

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.

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!

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

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'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.

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.

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.

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.

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.

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

Does the non-linearity come from the diode or does it come from the resistor?

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.

Isn't the diode linear only within a certain part of the VI graph?

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.

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.

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.

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.

> [...] 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.

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.

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.

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...

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.)

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.

just drive your optics hard enough, you'll see back-EMF

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.

I bet many of those audiophiles would either not tell the difference or love it if it was marketed accordingly.

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