Tortuga Preamps

George, I had thought that the Tortuga's calibration of the LDR's LED control current curve is invoked periodically by the user on an as-needed basis, not "actively" or on-the-fly.  If it's performed only periodically, how will this degrade SQ? 

Recluse, I enjoyed mine very much. It is very open and transparent. I was surprised to see that it measured so poorly. I have gone back to my active preamp due to selling my separate phono stage.

Love my Tortuga !

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