Tortuga Preamps

It’s an active circuit attached to the output, which is the audio signal, and not being match need calibrating at every increment of volume adjusted to stay calibrated.
If you have "say" 3 led/ldr’s (could be two or one, as they are not matched) of the 4 led/ldrs running at "x" impedance, the other/s may get over worked trying to keep up and visa versa which shortens their life span.
Also you need to use the NSL32SR2S to get low enough impedance to get the lowest volume.
Just look at the data sheets if you can understand them, of all that I have posted up many times here and at DiyAudio, and look at max 20mA brightness for the lowest impedance attained.

Cheers George

scm
Love my Tortuga !

That’s good stay with it, they are still way better than any other form of passive or active volume control.

Dartzeel use them the same way I do as their "Pleasure Control" in their $18k preamp
https://www.stereophile.com/solidpreamps/607dart/index.html
Half way down the page,https://6moons.com/audioreviews/dartzeel2/preamp_4.html explains the "Pleasure Control" (Lightspeed volume control), patents were never granted, I saw to that being the originator back in the 70’s 80’s

The only thing that can better them and the Lightspeed Attenuator, is direct connection between source and poweramp using the sources digital domain volume control, but these must be used at or above 75% to avoid any "bit stripping" IE: 16bit resolution down to 14bit and so on the lower you go with them.

Cheers George

Thanks for the elaboration,
Sounds intriguing.

Are these still being made and what is the link to purchase? 
Are these offered with real balanced connections.?

https://www.tortugaaudio.com/

Are these still being made and what is the link to purchase?
Are these offered with real balanced connections.?

Yes send a PM or there are many other ways just Google, or if you have the diy skills build one for yourself, as I've given all the instructions here.  
https://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-passive-preamp.html

And no I don't believe in xlr, unless your in a studio with with lots of noise problems, extra long runs of interconnects.
My customers use these if they need, XLR to RCA adapters, Neutirk being fair value for money, some are much less expensive 
 https://i.ebayimg.com/images/g/wrMAAOSwDk5UBLdo/s-l300.jpg

Cheers George