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
Has anyone compared the Lightspeed Attenuator to a digital volume control on a digital source? If so, is the Lightspeed Attenuator substantially better? I know you theoretically "lose bits" with a digital volume control, but I want to know if others have experienced a noticeable upgrade with the LSA over going amp-direct from a digital source...Thanks.
Hi Mcondon, if you can use the digital domain volume control within it's final 20% of full output, IE if it's 100 steps, then 80 or more you should not hear any bit stripping, if lower than 80 forget it your starting to go back to the days of good 14 bit of the first Marantz cdp which were pleasant, but no detail.
In theory if the digital domain volume control is over 80% or close to full output it should be the only thing better in transparency and honest to the source than the Lightspeed Attenuator, because you have removed another set of interconnects, and this is always a good thing.
Cheers George
Thos pesky little people are at it again, I've been sent a few sites where they are charging $10-$50 for the Lightspeed Attenuator circuit.
I have put it up free on DIY Forums, but they are out there trying to make money on someone else's I.P.
So here is the circuit again FREE so you can make one yourself if you up to it, and not pay for it. Hope the moderators allow it.

http://diyaudioprojects.com/Solid/DIY-Lightspeed-Passive-Attenuator/Lightspeed-Passive-Attenuator-Schematic.png

Cheers George
Thanks George, publishing your IP has been a benefit to many. Although I suppose some of "the many" don't realize how tough it is to match those LDR's. They could sell the circuit for as cheap as they can, but the overall question is can they build it well. I appreciate the efforts of the true DIY'ers that try, but frown upon those trying to cash in on your IP.
Thanks Clio, it's just the circuit diagram they are trying to sell, no components at all.
Cheers George