£100 analogue fibre optic audio lead - Page 1
Forum section: electronics / general

author: rthorntn
author_rank: Frequent Contributor
timestamp: June 30, 2015, 09:50:27 pm
content: https://www.kickstarter.com/projects/1536327222/lightleadtm-world-1st-analogue-optical-audio-cable/descriptionLooks like it's really for connecting musical instruments to amps but it's probably being lapped up by the audiophiles, you have to change the batteries every 18 hours!

author: edy
author_rank: Super Contributor
timestamp: July 01, 2015, 12:37:07 am
content: So does the electrical signal get transformed into amplitude modulation of the laser? Some type of opto-coupler? There has to be a frequency response curve to the electronics encoding the signal into light and then the reverse photodiode and necessary amp needed to bring the signal back to the proper dB No encoding, digitisation or modulation..So you wonder why they are making a different cable for different instruments. Geez... if it is so great, how the heck do you need a different cable for each instrument? It must have issues with frequency response and need to be set to work in certain ranges.I don't trust it one bit until I see them reveal more of the technical details and show the magic behind the current or independent audio lab testing.QuoteBut there is transformation of one energy to another and then back again. Surely that has to introduce issues as it would not be linear across all frequencies.Let's assume it works fine, the next question is does it offer any advantage over a properly shielded cable?

author: helius
author_rank: Super Contributor
timestamp: July 01, 2015, 12:49:03 am
content: Different instruments have different output levels, so a cable matched to each would be needed.Every optical cable has slightly different return loss, and it changes with cable flex, and they are terminated by hand with more variation. Calibrating AM response for all of that seems like it's losing. PWM would still be "analog" right?With stage instruments, the cables take a lot of abuse and don't last forever. One of the attractions of Monster is that they give a lifetime warranty on cables, which is a big deal when you wear one out every six months. Will these cables carry a warranty?

author: rthorntn
author_rank: Frequent Contributor
timestamp: July 01, 2015, 12:52:29 am
content: from the video "lets just switch to the lightlead and do SOMETHING SIMILAR", the mix sounds very different to my ears, boosted."the LightLead don't degrade over time like copper cables" is he talking about high temps degrading the sheathing on power cables, surely this doesn't apply to audio cables?I doubt there will be much of a warranty, there are a LOT more parts to lightlead, it might be relegated to the studio.

author: miguelvp
author_rank: Super Contributor
timestamp: July 01, 2015, 12:56:48 am
content: QuoteThey claim the path is all analog.Patent:http://patents.justia.com/patent/20150037047Edit more patents:https://www.google.com/patents/WO2007031794A1https://www.google.com/patents/US20100284168?(not his, disregard)https://www.google.com/patents/US20100003033https://www.google.com/patents/EP1941635A1https://www.google.com/patents/WO2008099208A1Edit: more current google patent link:https://www.google.com/patents/EP2833568A1They do mention PWM

author: Marco
author_rank: Super Contributor
timestamp: July 01, 2015, 01:13:40 am
content: Quote from: helius on July 01, 2015, 12:49:03 amJust use a little local feedback, the photodiode is pretty linear as is POF for audio frequencies (extremely lossy though). It's only a bunch of musical instruments.If XLR cables really get that easily damaged and POF is more robust I can see value in this.

author: miguelvp
author_rank: Super Contributor
timestamp: July 01, 2015, 01:51:44 am
content: Schematic from that last patent:U6 and U7 seem to drive the MCU to generate a PWM to feed into U5 to compensate something.U2 and U4 + are probably connected to VDD with a similar resistor network as U3 and U5 respectively

author: mikerj
author_rank: Super Contributor
timestamp: July 01, 2015, 11:59:48 am
content: Quote from: LightLeadDoesn't bode well if they have based the entire design on this invalid assumption. Where do I get this analogue light anyway? I don't think it exists as light is always quantised

author: Marco
author_rank: Super Contributor
timestamp: July 02, 2015, 08:04:55 am
content: What's the point in this tortuous schematic?How does this haven an advantage over simply buffering the AC input, adding a DC offset and using an opamp voltage->current circuit to drive the LED? Two opamps, a transistor and some passives and you're done.PS. oops, I guess it's to adapt the bias so the signal doesn't clip ... nevermind.

author: wreeve
author_rank: Unknown
timestamp: July 02, 2015, 08:48:34 am
content: If they really wanted to make money I would have thought the old phono lead would be a good application for this. £100 is entry level for the audiophools!

author: LightLead
author_rank: Newbie
timestamp: July 02, 2015, 10:37:13 am
content: Hi,I'm David Holmes the inventor of the LightLead.I thought i'd drop by to answer some questions you have, so here goes.Your questions are initalics."So does the electrical signal get transformed into amplitude modulation"Yes the electrical/optical signal is as simple as "voltage up light intensity up""So you wonder why they are making a different cable for different instruments."The different cables are for the different out impedance's of instruments. (Guitar high, microphone low)The difference is only the input stage, and the output stage of the reciver. The analogue transmission is the same."Let's assume it works fine, the next question is does it offer any advantage over a properly shielded cable?"Advantages are:No Induction.Electrical Isolation.No Capacitence (although i know some people like that)No Loading. (tested with piezo electric violin)Consitently the same sound every time its being used."Will these cables carry a warranty?"Yes, We offer a lifetime guarentee."the LightLead don't degrade over time like copper cables" is he talking about high temps degrading the sheathing on power cables, surely this doesn't apply to audio cables?”This is the capacitance build up in copper cables, every tiny fracture in the tiny copper wires acts as a capacitor, sucking frequencies away from your signal (high impeadance sources that is)I see you have a lot of old patents listed.The current granted patent is dated 2014"U6 and U7 seem to drive the MCU to generate a PWM to feed into U5 to compensate something."Didnt think we would need to go this deep!U7 is a signal detector. If no signal is present after 10mins the system shuts off to save battery.We may make this a user option or remove it altogether.U6 is the clever bit. It tells the MCU about the current between the two diodes when both diodes have zero signal.The PWM output from the MCU is to adjust the current of the two diodes so that the light output from both diodes is exactly the same. (temperature and manufacture processes all add different characteristics to each diode)THERE IS NO PWM IN THE LIGHT SIGNAL TRANSMITTED."Analogue Light isn't affected as it travels down the fibre. Doesn't bode well if they have based the entire design on this invalid assumption."Most POF has a minimum bend radius that would affect light traveling through it. its normally 6cm radius before light is affected. Our Prototype uses 4cm and we have never had an issue with cable flexing. We are also testing 4mm bend radius optical cable and 2mm bend radius optical cable."Where do I get this analogue light anyway? I don't think it exists as light is always quantised"This is an age old argument. 'Waves or particles'. dont think i could win this argument, I like to think of light as waves. We mean anaologue as in not modulated on a carrier or PWM or digitised. its simply 'brighter light, dimmer light'NOT 'on , off light'."What's the point in this tortuous schematic? How does this haven an advantage over simply buffering the AC input, adding a DC offset and using an opamp voltage->current circuit to drive the LED? Two opamps, a transistor and some passives and you're done."Surprisingly the DC offset driving an led was done in 1986! And it was even for a guitar lead (and i thought i had a new idea) unfortunately it will only get you about 70db of signal. Putting that in a high gain amp is pretty niosey, and clippy. Lightlead is a new concept in analogue audio and it sounds fantastic. You just have to hear it, you can feel the difference.If you have any questions i'm happy to answer all your questions.David HolmesIconic Sound

author: tszaboo
author_rank: Super Contributor
timestamp: July 02, 2015, 11:07:59 am
content: Very interesting approach. If I understand correctly, e-guitars have no active electronics built in. So would it make sense to just build an amplifier, which similarly just plugs into the Jack of the guitar, buffer it, and send down the signal on a balanced transmission line?Can you provide a bode plot of the analog optical system?

author: deephaven
author_rank: Frequent Contributor
timestamp: July 02, 2015, 11:45:19 am
content: David,Do you have any specs regarding frequency response, noise, linearity?

author: mikerj
author_rank: Super Contributor
timestamp: July 02, 2015, 11:55:36 am
content: Quote from: LightLead on July 02, 2015, 10:37:13 amThe point was that optical fibres can suffer from a multitude of non-linear effects, so suggesting it's somewhat of a "perfect" transmission medium is probably a bit of a stretch.Personally I think your idea is pretty good, and could offer some real advantages, but having seen how cables get treated on stage the fibre and it's terminations had better be well ruggedised!Quote from: LightLead on July 02, 2015, 10:37:13 amTo be fair that was just a tongue in cheek comment, not a criticism, but I appreciate the reply

author: Marco
author_rank: Super Contributor
timestamp: July 02, 2015, 02:45:25 pm
content: Quote from: LightLead on July 02, 2015, 10:37:13 amPretty sure I couldn't hear or feel the difference compared to a digital solution, but I appreciate the ingenuity involved in keeping it analogue without needing very large DC bias currents.Was it really necessary to use two fibres? Couldn't you have done this with 2 different colour LEDs and colour filters?

author: miguelvp
author_rank: Super Contributor
timestamp: July 02, 2015, 04:07:38 pm
content: Two fibers for redundancy, if you break one it will still work, probably not as good but you can keep on playing.Also ground feedback will go away, or if there is some amp failing (as in the mains touching the input jack from abuse during transport) it won't kill your lead guitarist

author: fcb
author_rank: Super Contributor
timestamp: July 02, 2015, 04:35:16 pm
content: Nice piece of thinking - good luck with it.I've just backed a 20ft/6M Lightlead.

author: wraper
author_rank: Unknown
timestamp: July 02, 2015, 04:37:48 pm
content: No way this will be better in signal quality than ADC->digital fiber->DAC. Therefore audifool bullshit. Zero capacitance and zero loading is marketing bullshit too.

author: wraper
author_rank: Unknown
timestamp: July 02, 2015, 04:43:16 pm
content: QuoteI guess optic fiber have more microphonics and is affected from bending much more than simple copper cable.http://www.thefoa.org/tech/ref/fiber/BIfiber.htmlQuoteMarketing bullshit again as vinyl have awful quality. Rather someone likes Vinyl sound or is ignorant audiofool.QuoteMore marketing bullshit and a blatant lie as optic fiber degrade tremendously.

author: Marco
author_rank: Super Contributor
timestamp: July 02, 2015, 06:16:50 pm
content: Quote from: miguelvp on July 02, 2015, 04:07:38 pmIt's close to two half-wave rectified signals ... so not really.

author: edy
author_rank: Super Contributor
timestamp: July 02, 2015, 06:33:02 pm
content: I'm still curious as to what effect the electronic -> optical -> electronic conversion has on the signal. A frequency response curve would be ideal, or even an oscilloscope showing traces of the generated signal (some square, sine and triangle or saw-tooth) next to the output signal after passing through the LightLead cable and also regular cable (would use up 3 channels to display (1) generated input signal (2) 20 ft of LightLead, (3) 20 ft shielded audio cable). This could be done while altering the input frequency to see what, if any, effect it has. You could even bend the LightLead cable and audio cable various ways and see what happens.Is there any dynamic compression of the signal? "Rounding" of abrupt changes to the signal which would affect square waves or higher frequencies? Delay introduced in the signal? To be convinced, I'd like to SEE IT on an oscilloscope, and not just HEAR IT as our ears are not going to be as accurate and can be tricked.The other question is, if we just don't want our guitarist to be electrocuted, wouldn't it be enough to introduce a small opto-coupler-like device anywhere along the signal path? Just plug regular audio cables into a box.... One goes to the guitar, another to the amp. The box isolated the signal electrically, using opto-coupler or other electric isolation methods (electromagnetic... like a transformer). Why bother with having a long optical cable?If you could ship out a sample cable to Dave "The Crazy Aussie Bloke" he could do this on EEVBlog with a frequency generator and show us the signals on his oscilloscopes.Now if there *IS* a change in the signal, we have to convince ourselves that for the audio frequencies being used it is not relevant, or that the effects being introduced (like smoothing or compression) actually are more pleasant sounding and may be desirable, despite the non-linear response. And we may actually prefer optic for additional reasons like avoiding noise bleeding into the system, interference and electrocuting our guitarist (which may not be a bad idea depending on whether you like him/her or not).

author: ehughes
author_rank: Frequent Contributor
timestamp: July 02, 2015, 07:22:01 pm
content: Perhaps the inventor can show some real scientific results?Double Blind Study of the perceived "Quality" difference between this and "degraded" patch cables?Real measurements of the transmission line characteristics?>>Frequency Response?, Group Delay Distortion?, Noise floor?I am not sure I would sell this as something with Vinyl like quality.....

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 02, 2015, 07:31:05 pm
content: Quote from: ehughes on July 02, 2015, 07:22:01 pmYeah, it is just another pseudo-scientific "product" with no hard data.Either the data is too embarrassing to publish, or they haven't actually made any objective measurements, or they assume the customers are too dumb to care. None of the possibilities speaks very well of them, IMHO.I no longer marvel at how these kinds of things survive.And I have also ceased wondering how people can come along with this kind of business model.Just further support for my World View which is essentially the 2nd Law of Thermodynamics: Entropy Happens.

author: Delta
author_rank: Super Contributor
timestamp: July 04, 2015, 10:29:06 am
content: Optical fibre cables in a stage environment = idiocy of the highest order.Send one to Roger Daltry and see how long it lasts on his mic!

author: madires
author_rank: Super Contributor
timestamp: July 04, 2015, 11:15:15 am
content: Quote from: edy on July 02, 2015, 06:33:02 pmYou have different kinds of distortion and attenuation and they differ greatly with the fiber type. Of course they will impact any signal. While a digital signal is still readable and can be regenerated, an analog signal can't be fixed. And the good fiber types aren't used for end users because they are simply too fragile. So end users get thick plastic fibers, which can take more abuse and have a lower bending radius, but are the worst type (toslink for eample).

author: fcb
author_rank: Super Contributor
timestamp: July 04, 2015, 04:12:26 pm
content: When I was involved in analog audio over fibre back in the early-mid 90's, we mainly used FM to modulate the audio - it was very good, and we could multiplex many channels of audio.I've also sent audio over fibre in much the same way as the LightLead - it also sounds very good, and if they have fixed lengths and no need to for an AGC, it will be good. Will be at as good as using star-quad or a digital system - no, but it might have colourations that the end user actually likes (much like valve amps).I've backed the project as I think it has merit, although I think there is a certain amount poetic-license applied to the KS promotional material...

author: Yago
author_rank: Frequent Contributor
timestamp: July 09, 2015, 01:02:54 pm
content: Quote from: rthorntn on July 01, 2015, 12:52:29 amI though very much the same.Only got a shite speaker here, but I swear not only is the eq different, there are reverb and chorus effects added to the sound for the light lead test.

author: fcb
author_rank: Super Contributor
timestamp: July 09, 2015, 04:47:20 pm
content: I suspect that the single biggest (sonic) benefit of the lightlead will be the inclusion of buffer amplifier in the chain - guitar amps vary wildly in their input impedance and this has (IMHO) the most significant effect on the 'tone'.It's pretty immaterial as the have raised about 2% of the total..

author: LightLead
author_rank: Newbie
timestamp: July 26, 2015, 02:04:45 pm
content: Hi, Ive added a new video which may be of interest tohttps://www.kickstarter.com/projects/1536327222/lightleadtm-world-1st-analogue-optical-audio-cable

author: fcb
author_rank: Super Contributor
timestamp: July 26, 2015, 02:41:35 pm
content: You quote on the KS page:"We use a patented optical analogue technology.No encoding, digitisation or modulation.The signal travels down the fiber as light!"What's the patent number??

author: LightLead
author_rank: Newbie
timestamp: July 26, 2015, 02:50:40 pm
content: Here it is, i think its already been pulled out on a previous post.Light Emission CircuitEP 2833568 A1http://google.com/patents/US20150037047?cl=enhttp://google.com/patents/EP2833568A1?cl=en

author: fcb
author_rank: Super Contributor
timestamp: July 27, 2015, 08:27:35 am
content: Interesting Patent - so it's just a uP controlled active bias.102dB S/N would be very impressive..

author: coppice
author_rank: Super Contributor
timestamp: July 27, 2015, 08:33:34 am
content: Quote from: fcb on July 27, 2015, 08:27:35 amWhat would be impressive about 102dB SNR? Even with quite small signals, where noise is harder to control, 102dB is very mundane these days.

author: fcb
author_rank: Super Contributor
timestamp: July 27, 2015, 08:51:13 pm
content: Quote from: coppice on July 27, 2015, 08:33:34 amAgree, 102dB SNR is a mundane or even poor for an ADC/DAC or even a balanced audio signal - but not for a EO-OE system.

author: LightLead
author_rank: Newbie
timestamp: July 28, 2015, 06:18:37 pm
content: We are at 104db S/Nwe are constantly achieving better results as optical technology advances.David Holmes.Iconic Sound

author: LightLead
author_rank: Newbie
timestamp: August 06, 2015, 10:59:52 pm
content: There has been an interesting developement!https://www.kickstarter.com/projects/1536327222/lightleadtm-world-1st-analogue-optical-audio-cable

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 07, 2015, 01:19:47 am
content: Quote from: LightLead on August 06, 2015, 10:59:52 pmAnd apparently it will only cost you £10 to find out what that is!

author: rthorntn
author_rank: Frequent Contributor
timestamp: August 07, 2015, 01:23:02 am
content: I think the development is a kickstarter special price of 35 quid.

author: LightLead
author_rank: Newbie
timestamp: August 07, 2015, 07:28:50 am
content: I was actually referring to the new design model going to the printers.... but yes £35 is also exciting!

author: fcb
author_rank: Super Contributor
timestamp: August 07, 2015, 11:08:34 am
content: I'm an early backer of this KS.IMHO your making a mistake dropping the price to 1/3rd - I don't think this is the main reason your KS is stuck at 5% of target. I don't think you've made or can make a convincing case for this product - it's niche and it's one more thing to go wrong (and has batteries in it which scares people).At £35 you will be making a huge loss on this project as you'll have to make in the region of 2000 units - your BOM is going to be thick-end of the £35 and you'll have to consider hard tooling (certainly if you want to make more in the future).So if you've got the money for hard-tooling, why not just make some aluminium tools and produce a smaller batch for the niche.