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 in italics.
"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 Holmes
Iconic Sound