LightSpeed Attenuator vs. GoldPoint SA1X

"Yuhengdu_tiger
How can a ldr resistor be stable over time? I think the ldr preamp are very subtle since it needs to convert electric to photo and then convert photo to resistance."

First of all it's not just ldr, it's 4 x quad matched led/ldr in a hermetically sealed packages with 4 legs on each.
2 legs for led, and 2 legs for ldr (resistor)

"Electric" is the LED (Light Emitting Diode) portion, and "photo" is the LDR (Light Dependent Resistor)

Here is the circuit diagram of it (2nd pic) and how to build one if you have the skills.
[url]http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp.html[/url]

The MkII Lightspeed prototype has been powered on now 24/7 for over 6 years and is still in perfect calibration (stable), and we've never had one back out of hundreds for recalibration.
Just a couple of fried ones from owners doing strange things with the power supplies that have no basic electronic knowledge and trying the wrong thing.

Cheers George

Thanks for your explanation George. How can you ensure the amount of light captured by the LDR is accurate and fine-grained enough then?

This has been covered many times here and on the DIYAudio forum threads.
It's led's are powered by well regulated linear supply.
Many blind A/B comparisons have been done even with Li/Ion battery v the supplied linear power supply, and listeners could not reliably detect the difference, even Sam Tellig of Stereophile came to the same conclusions, with his own Lightspeed after getting a battery pack as well.
As ldr's themselves are self damping to "fine gained" changes as their reaction times to light changes are quite slow.
The only difference of power supplies that could be reliably detected was with SMP power supplies, and this was because of their switching noise infiltrating into the ground plane and into the output stage, not into the led's

Cheers George

Thank you George!

Yuheng