Lightspeed Attenuator - Best Preamp Ever?


The question is a bit rhetorical. No preamp is the best ever, and much depends on system context. I am starting this thread beacuase there is a lot of info on this preamp in a Music First Audio Passive...thread, an Slagle AVC Modules...thread and wanted to be sure that information on this amazing product did not get lost in those threads.

I suspect that many folks may give this preamp a try at $450, direct from Australia, so I thought it would be good for current owners and future owners to have a place to describe their experience with this preamp.

It is a passive preamp that uses light LEDs, rather than mechanical contacts, to alter resistance and thereby attenuation of the source signal. It has been extremely hot in the DIY community, since the maker of this preamp provided gernerously provided information on how to make one. The trick is that while there are few parts, getting it done right, the matching of the parts is time consuming and tricky, and to boot, most of use would solder our fingers together if we tried. At $450, don't bother. It is cased in a small chassis that is fully shielded alloy, it gets it's RF sink earth via the interconnects. Vibration doesn't come into it as there is nothing to get vibrated as it's passive, even the active led's are immune as they are gas element, no filaments. The feet I attach are soft silicon/sorbethane compound anyway just in case.

This is not audio jewelry with bling, but solidly made and there is little room (if any) for audionervosa or tweaking.

So is this the best preamp ever? It might be if you have a single source (though you could use a switch box), your source is 2v or higher, your IC from pre-amp to amp is less than 2m to keep capaitance low, your amp is 5kohm input or higher (most any tube amp), and your amp is relatively sensitive (1v input sensitivity or lower v would be just right). In other words, within a passive friendly system (you do have to give this some thought), this is the finest passive preamp I have ever heard, and I have has many ranging form resistor-based to TVCs and AVCs.

In my system, with my equipment, I think it is the best I have heard passive or active, but I lean towards prefering preamp neutrality and transparency, without loosing musicality, dynamics, or the handling of low bass and highs.

If you own one, what are your impressions versus anything you have heard?

Is it the best ever? I suspect for some it may be, and to say that for a $450 product makes it stupidgood.
pubul57
The Lightspeed can never go to complete zero volume (there is always a whisper at min) and in rare very high gain systems such as Fins the volume will be down around 9 or 8 o'clock low for normal listening level, and this will give the impression of more "gain" than a passive that can go to complete zero level.


As "Fin" (Andrew) contacted me about this last week, he gave his system parameters to me. And as you can see below he has a s**t load of gain, with effecient speakers.

They are:
source >2.5v out
power amp <1v in.
As you can see he needs only 1 volt in to for his amp to give it's 100w full power.
And he has more than 2.5v from the source.
And because of this the Lightspeed is down low for normal listening.

Cheers George

Hi all, I should clarify that the slagleformer pre suffered similar downsides, being very basic and also being quite loud on low settings. The Slagleformers modules are available with, I think, another 12db attenuation which was an avenue I was exploring. The volume issue is not a big issue... I can still play music at levels I want to most of the time. Its probably psychological more than anything, a feeling there is something going to waste or not fully utilised until the volume is at 9 oclock or so and a niggling but uninformed concern that passives and actives work best in the middle of their operating range? However both these units work very well at the bottom of their ranges, regards, Andrew
No nothing going to waste Finn (Andrew) as you have 100kohm input impedance on your amp, so it doesn't mater where the volume is set on the Lightspeed you are getting great impedance matching still over the entire range.

This is a classic quote from Nelson Pass.
(proclaimed god of audio)
"We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."

Cheers George
Ha! Love your comments George. As you know I have tried your passive three times, but just prefer my tube active. But, I do like the way your passive sounds and it is a killer value. Just not as real sounding as my active.

I soooo wanted to like your passive as much to save money and simplify.
I tried three times as I really hoped everything I see here would be true for me. I have no bias to spend more money or take up more space:)

Glad to see so many happy LS owners and the thread staying so vibrant. This is a good thing for all us Aphiles.