LightSpeed Attenuator vs. GoldPoint SA1X

I am looking for a passive preamp. How would lightspeed attenuator compared to GoldPoint sa1x or Luminious audio axiom II?


Hi Yuhengdu, Here's one below on the Luminous Audio Axiom. I'll look at some other sites on Lightspeed threads for you for the Goldpoint comparison if there is one I'll post it here.

Cheers George

Here is another comparison with similar DIY Slagle Autoformer Modules TVC based passive preamp like the Axiom. Still looking for one with the Goldpoint.

Cheers George
Thank you! So lightspeed is ldr based? How about the tortuga preamp?

Yes there are a few clones trying to get around having not to quad match the LDR's which is very labour intensive.
Ones I know just dual match (the series and the shunt ldr's) which is half way there to get the best out of it.

And then some now don't match at all, and use a forced matching auto calibration type circuit circuit (like a active feedback circuit) to force match the LED/LDR's. This saves a lot of labour. But this can be desctructive over time to the led/ldr's (as I stated in the Lightspeed diy thread linked) and then it can also lead to not having a very low lowest level volume. Like revving your car passed it's redline all the time, something's got to give after a while.

I have found quad matching is the only way to go, to still use the labour intensive way of hand quad matching the series and shunt led/led's over 5 different current points, it the only way for me, and gives the best reliability, lowest low level volume and a nice logarithmic feel to the volume control progression, and best sound.

Cheers George
Is it impossible to do a balanced version of LDR passive volume control? Thanks.

XLR has an advantage only over single ended if the interconnects are very long (EG: 5-10mts) then it's only a noise advantage, if anything single ended in most cases sounds better because of less electronics in the signal path that XLR needs at both output and input of the source and poweramp.

Also to make a passive Lightspeed balanced it's exponentially much harder, these are the reasons I don't make them, and they're not suitable for 10mts of interconnects in SE or XLR form.
I have put up a diy circuit for builders to make their own XLR (balanced) Lightspeed if they wish here.

Cheers George
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.

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.

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!