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
I thought "everything" was over priced when I heard the $135 Pot-in-a-Box (expensive Noble pots used on the vintage Audio Research SP-6) sold by Roger Modjeski. Given my two line stages at the time were in the $5-7k range a few years ago, it seemed like a bloody good deal! The LSA just happens to take a "simple" passive volume control to the nth degree, and as you have discovered, in the right system can be a pretty magical way of controlling volume.
Devilboy - I note that you have a Bent Audio Tap (as well as the Metrum Octave). Could you do a quick comparison of the LSA and the Bent? That I believe would be of interest to everyone on this thread.
I can now see why you preferred the tube preamp that has gain Grannyring. As your Aesthetix Atlas power amp has well below the standard input sensitivity at 3.1v. The input impedance was fine at 470k or higher (as you measured) but most amps on the market need 2v or less input sensitivity to drive them, your amp needs 3.1v most sources only have 2v (Red Book standard) so this amp is not suited to preamps that are unity gain active or passive.
If you could of raised the gain of the Atlas by a higher "gain" input tube or lowering the feedback, way so it became 2v or less input sensitivity then I would dare say that you may not have sold your Lightspeed Attenuator.

Cheers George